I am proposing to engage on a project regarding mains voltage 'purity'
(and absence of ) with regard to audible clicks and pops in high-end
professional and hi-fi audio equipment.

Typical EMC filters operate in the RF band and are threfore no use to
filter audio 'in band' noise that can travel through transformer
interwinding capacitance etc.

I have found some of the TI INA series that will with suitable
preconditioning, tolerate mains voltages and give excellent common-mode
etc rejection. So assembling a 'preamp' front end should be no problem.

What I will need to do however is to filter all the mains frequencies
and harmonics to a very large degree.

I imagine I would need for example to null 50 Hz +/- 2 Hz to ~ -100dB. I
have done only a little DSP ( I can't see it happening with analogue
filters ) and I don't even know where to begin with such a severe filter
without affecting the pass-band. Same will go for harmonics up to some
serious number.

Can  anyone offer some advice as to algorithms ( number of cycles for
such a deep notch ) and even better, a readily available eval board upon
which it could be set up ? Remember I only need to 'hear' audio band, so
44.1 or 48 kHz sampling should be OK esp given the oversampling ADCs
today.

Many thanks,    Graham

Eeyore wrote:
> I am proposing to engage on a project regarding mains voltage 'purity'
> (and absence of ) with regard to audible clicks and pops in high-end
> professional and hi-fi audio equipment.
> 
> Typical EMC filters operate in the RF band and are threfore no use to
> filter audio 'in band' noise that can travel through transformer
> interwinding capacitance etc.
> 
> I have found some of the TI INA series that will with suitable
> preconditioning, tolerate mains voltages and give excellent common-mode
> etc rejection. So assembling a 'preamp' front end should be no problem.
> 
> What I will need to do however is to filter all the mains frequencies
> and harmonics to a very large degree.
> 
> I imagine I would need for example to null 50 Hz +/- 2 Hz to ~ -100dB. I
> have done only a little DSP ( I can't see it happening with analogue
> filters ) and I don't even know where to begin with such a severe filter
> without affecting the pass-band. Same will go for harmonics up to some
> serious number.
> 
> Can  anyone offer some advice as to algorithms ( number of cycles for
> such a deep notch ) and even better, a readily available eval board upon
> which it could be set up ? Remember I only need to 'hear' audio band, so
> 44.1 or 48 kHz sampling should be OK esp given the oversampling ADCs
> today.

How does mains noise get into the equipment? Power supplies are filtered 
  and regulated, so any noise you experience must enter by another 
route. You might look into ferro-resonant transformers. These are 
primarily intended to regulate load voltage, but they also suppress 
voltage spikes. http://www.elect-spec.com/trnsreg.htm has examples.

A capacitive shield between primary and secondary of the power 
transformer may be all you need. Isolation transformers are built that way.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

On Thu, 21 May 2009 02:54:36 +0100, Eeyore wrote:

> I am proposing to engage on a project regarding mains voltage 'purity'
> (and absence of ) with regard to audible clicks and pops in high-end
> professional and hi-fi audio equipment.
> 
> Typical EMC filters operate in the RF band and are threfore no use to
> filter audio 'in band' noise that can travel through transformer
> interwinding capacitance etc.
> 
> I have found some of the TI INA series that will with suitable
> preconditioning, tolerate mains voltages and give excellent common-mode
> etc rejection. So assembling a 'preamp' front end should be no problem.
> 
> What I will need to do however is to filter all the mains frequencies
> and harmonics to a very large degree.
> 
> I imagine I would need for example to null 50 Hz +/- 2 Hz to ~ -100dB. I
> have done only a little DSP ( I can't see it happening with analogue
> filters ) and I don't even know where to begin with such a severe filter
> without affecting the pass-band. Same will go for harmonics up to some
> serious number.
> 
> Can  anyone offer some advice as to algorithms ( number of cycles for
> such a deep notch ) and even better, a readily available eval board upon
> which it could be set up ? Remember I only need to 'hear' audio band, so
> 44.1 or 48 kHz sampling should be OK esp given the oversampling ADCs
> today.
> 
> Many thanks,    Graham

This sounds like an adventure into audiophoolery, which isn't what I'd 
expect of you.

What, exactly, are you planning on filtering, and what are you planning 
on filtering it against?

I suppose that you could filter your power supply rail with a supply that 
has infinite rejection at all the power line harmonics -- but it seems 
that a good switcher followed by a good linear regulator for clean up 
would pound the power-line stuff down by many tens of dB.

If you absolutely had to get it down further you could incorporate a 
resonant element in the feedback of the linear regulator, arranged to 
provide a good notch.  Doing this with a DSP may just make sense in that 
case.

Filtering anything else sounds like flat-out magic.

And finally, if it's clicks and pops you're trying to eliminate, that 
would seem to indicate a problem with transients on the line, which 
aren't things that you're going to notch out.

-- 
http://www.wescottdesign.com

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

>I am proposing to engage on a project regarding mains voltage 'purity'
>(and absence of ) with regard to audible clicks and pops in high-end
>professional and hi-fi audio equipment.
>
>Typical EMC filters operate in the RF band and are threfore no use to
>filter audio 'in band' noise that can travel through transformer
>interwinding capacitance etc.
>
>I have found some of the TI INA series that will with suitable
>preconditioning, tolerate mains voltages and give excellent common-mode
>etc rejection. So assembling a 'preamp' front end should be no problem.
>
>What I will need to do however is to filter all the mains frequencies
>and harmonics to a very large degree.
>
>I imagine I would need for example to null 50 Hz +/- 2 Hz to ~ -100dB. I
>have done only a little DSP ( I can't see it happening with analogue
>filters ) and I don't even know where to begin with such a severe filter
>without affecting the pass-band. Same will go for harmonics up to some
>serious number.
>
>Can  anyone offer some advice as to algorithms ( number of cycles for
>such a deep notch ) and even better, a readily available eval board upon
>which it could be set up ? Remember I only need to 'hear' audio band, so
>44.1 or 48 kHz sampling should be OK esp given the oversampling ADCs
>today.

A sharp filter for just one frequency is very easy. One ore more
biquad sections (5 multiplies & adds per biquad) are sufficient. That
doesn't take a lot of processing power. A cheap & simple ARM
microcontroller will do.

Still, you should be aware of phase changes near the filter
frequencies. I'm quite sure this will alter the sound.

However I have to go along with Tim. Filtering 50Hz harmonics is not
going to help. The plops and clicks you mention are not a multiples of
50Hz. These are just random spikes on the mains. If these spikes end
up in your audio circuitry, then you most likely have a ground loop or
another ground related problem somewhere. It means that the current
from the spike shares a return path with your audio signal. 

-- 
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
                     "If it doesn't fit, use a bigger hammer!"
--------------------------------------------------------------

Jerry Avins wrote:

> Eeyore wrote:
> > I am proposing to engage on a project regarding mains voltage 'purity'
> > (and absence of ) with regard to audible clicks and pops in high-end
> > professional and hi-fi audio equipment.
> >
> > Typical EMC filters operate in the RF band and are threfore no use to
> > filter audio 'in band' noise that can travel through transformer
> > interwinding capacitance etc.
> >
> > I have found some of the TI INA series that will with suitable
> > preconditioning, tolerate mains voltages and give excellent common-mode
> > etc rejection. So assembling a 'preamp' front end should be no problem.
> >
> > What I will need to do however is to filter all the mains frequencies
> > and harmonics to a very large degree.
> >
> > I imagine I would need for example to null 50 Hz +/- 2 Hz to ~ -100dB. I
> > have done only a little DSP ( I can't see it happening with analogue
> > filters ) and I don't even know where to begin with such a severe filter
> > without affecting the pass-band. Same will go for harmonics up to some
> > serious number.
> >
> > Can  anyone offer some advice as to algorithms ( number of cycles for
> > such a deep notch ) and even better, a readily available eval board upon
> > which it could be set up ? Remember I only need to 'hear' audio band, so
> > 44.1 or 48 kHz sampling should be OK esp given the oversampling ADCs
> > today.
>
> How does mains noise get into the equipment?

That's part of the project. To find out. I suspect many different possibilities
but we can't rebuild the equipment so we need to find out what it's suspectible
too. Plus we expect to be tackling this problem for many types of equipment.


> Power supplies are filtered
>   and regulated, so any noise you experience must enter by another
> route. You might look into ferro-resonant transformers. These are
> primarily intended to regulate load voltage, but they also suppress
> voltage spikes. http://www.elect-spec.com/trnsreg.htm has examples.
>
> A capacitive shield between primary and secondary of the power
> transformer may be all you need. Isolation transformers are built that way.

Yup I know. An ultra-isolation transformer will be part of our 'toolkit' too.
I've used them before.But we need to know what interference is on the AC line.

Graham

Tim Wescott wrote:

> On Thu, 21 May 2009 02:54:36 +0100, Eeyore wrote:
>
> > I am proposing to engage on a project regarding mains voltage 'purity'
> > (and absence of ) with regard to audible clicks and pops in high-end
> > professional and hi-fi audio equipment.
> >
> > Typical EMC filters operate in the RF band and are threfore no use to
> > filter audio 'in band' noise that can travel through transformer
> > interwinding capacitance etc.
> >
> > I have found some of the TI INA series that will with suitable
> > preconditioning, tolerate mains voltages and give excellent common-mode
> > etc rejection. So assembling a 'preamp' front end should be no problem.
> >
> > What I will need to do however is to filter all the mains frequencies
> > and harmonics to a very large degree.
> >
> > I imagine I would need for example to null 50 Hz +/- 2 Hz to ~ -100dB. I
> > have done only a little DSP ( I can't see it happening with analogue
> > filters ) and I don't even know where to begin with such a severe filter
> > without affecting the pass-band. Same will go for harmonics up to some
> > serious number.
> >
> > Can  anyone offer some advice as to algorithms ( number of cycles for
> > such a deep notch ) and even better, a readily available eval board upon
> > which it could be set up ? Remember I only need to 'hear' audio band, so
> > 44.1 or 48 kHz sampling should be OK esp given the oversampling ADCs
> > today.
> >
> > Many thanks,    Graham
>
> This sounds like an adventure into audiophoolery, which isn't what I'd
> expect of you.

No it's not. It's come about as a requirement from a real recording studio.


> What, exactly, are you planning on filtering, and what are you planning
> on filtering it against?

That's what we need to find out. Where are the clicks and pops getting in. We
can't randomly spend the client's cash trying this and that. It needs to be a
scientific investigation.


> I suppose that you could filter your power supply rail with a supply that
> has infinite rejection at all the power line harmonics -- but it seems
> that a good switcher followed by a good linear regulator for clean up
> would pound the power-line stuff down by many tens of dB.

The power supply rail is generated inside the console in this case from a
balanced AC power feed. NO changes are possible.


> If you absolutely had to get it down further you could incorporate a
> resonant element in the feedback of the linear regulator, arranged to
> provide a good notch.  Doing this with a DSP may just make sense in that
> case.

I want the DSP to analyse what's going into the console PSU so I can see what
needs to be addressed and where.


> Filtering anything else sounds like flat-out magic.

Fine, come round to S. London and listen for yourself.


> And finally, if it's clicks and pops you're trying to eliminate, that
> would seem to indicate a problem with transients on the line, which
> aren't things that you're going to notch out.

Yes it does seem to be audio in band transients and my colleague and I have
several ideas how it's getting into the audio and have already explored in
some depth but we need more specialist tools to find the exact path.

Graham

Nico Coesel wrote:

> Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
>
> >I am proposing to engage on a project regarding mains voltage 'purity'
> >(and absence of ) with regard to audible clicks and pops in high-end
> >professional and hi-fi audio equipment.
> >
> >Typical EMC filters operate in the RF band and are threfore no use to
> >filter audio 'in band' noise that can travel through transformer
> >interwinding capacitance etc.
> >
> >I have found some of the TI INA series that will with suitable
> >preconditioning, tolerate mains voltages and give excellent common-mode
> >etc rejection. So assembling a 'preamp' front end should be no problem.
> >
> >What I will need to do however is to filter all the mains frequencies
> >and harmonics to a very large degree.
> >
> >I imagine I would need for example to null 50 Hz +/- 2 Hz to ~ -100dB. I
> >have done only a little DSP ( I can't see it happening with analogue
> >filters ) and I don't even know where to begin with such a severe filter
> >without affecting the pass-band. Same will go for harmonics up to some
> >serious number.
> >
> >Can  anyone offer some advice as to algorithms ( number of cycles for
> >such a deep notch ) and even better, a readily available eval board upon
> >which it could be set up ? Remember I only need to 'hear' audio band, so
> >44.1 or 48 kHz sampling should be OK esp given the oversampling ADCs
> >today.
>
> A sharp filter for just one frequency is very easy. One ore more
> biquad sections (5 multiplies & adds per biquad) are sufficient. That
> doesn't take a lot of processing power. A cheap & simple ARM
> microcontroller will do.
>
> Still, you should be aware of phase changes near the filter
> frequencies.

Of course.

> I'm quite sure this will alter the sound.

I'm not interested in the 'sound' of the mains other than to see disturbances
on it in the audio band.


> However I have to go along with Tim. Filtering 50Hz harmonics is not
> going to help. The plops and clicks you mention are not a multiples of
> 50Hz.

That's why I want to eliminate the 50 , 100 , 150 Hz etc so I can see what
they ARE.

> These are just random spikes on the mains. If these spikes end
> up in your audio circuitry, then you most likely have a ground loop or
> another ground related problem somewhere. It means that the current
> from the spike shares a return path with your audio signal.

Trust me, my colleague and I know all about ground loops, technical earths
etc and have even completely Faraday caged several studios.

I do not believe it has anything to do with grounds on the basis of what I've
seen.

What I'd really like to know is just where I can find info on doing what I
wanted to do, i.e. perform sharp notch filters with a narrowish bandwidth. I
do know what I'm doing in terms of trying to analyse the problem, I just need
some help with the DSP.

Graham

On a sunny day (Thu, 21 May 2009 02:54:36 +0100) it happened Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote in
<4A14B45B.7CDCFC35@hotmail.com>:

>I am proposing to engage on a project regarding mains voltage 'purity'
>(and absence of ) with regard to audible clicks and pops in high-end
>professional and hi-fi audio equipment.
>
>Typical EMC filters operate in the RF band and are threfore no use to
>filter audio 'in band' noise that can travel through transformer
>interwinding capacitance etc.
>
>I have found some of the TI INA series that will with suitable
>preconditioning, tolerate mains voltages and give excellent common-mode
>etc rejection. So assembling a 'preamp' front end should be no problem.
>
>What I will need to do however is to filter all the mains frequencies
>and harmonics to a very large degree.
>
>I imagine I would need for example to null 50 Hz +/- 2 Hz to ~ -100dB. I
>have done only a little DSP ( I can't see it happening with analogue
>filters ) and I don't even know where to begin with such a severe filter
>without affecting the pass-band. Same will go for harmonics up to some
>serious number.
>
>Can  anyone offer some advice as to algorithms ( number of cycles for
>such a deep notch ) and even better, a readily available eval board upon
>which it could be set up ? Remember I only need to 'hear' audio band, so
>44.1 or 48 kHz sampling should be OK esp given the oversampling ADCs
>today.
>
>Many thanks,    Graham

Dear Rabit:
 http://panteltje.com/panteltje/xpequ/humfilter-0.1.tgz

Actually it is just an interface I wrote to the code of somebody else,
the original was at http://www.abelian.demon.co.uk/humfilt/
but no longer seems to respond...

It is pretty good rejection, but does affect the sound.
C code, of coure.

Eeyore wrote:
> 
> Nico Coesel wrote:
> 
>> Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
>>
>>> I am proposing to engage on a project regarding mains voltage 'purity'
>>> (and absence of ) with regard to audible clicks and pops in high-end
>>> professional and hi-fi audio equipment.
>>>
>>> Typical EMC filters operate in the RF band and are threfore no use to
>>> filter audio 'in band' noise that can travel through transformer
>>> interwinding capacitance etc.
>>>
>>> I have found some of the TI INA series that will with suitable
>>> preconditioning, tolerate mains voltages and give excellent common-mode
>>> etc rejection. So assembling a 'preamp' front end should be no problem.
>>>
>>> What I will need to do however is to filter all the mains frequencies
>>> and harmonics to a very large degree.
>>>
>>> I imagine I would need for example to null 50 Hz +/- 2 Hz to ~ -100dB. I
>>> have done only a little DSP ( I can't see it happening with analogue
>>> filters ) and I don't even know where to begin with such a severe filter
>>> without affecting the pass-band. Same will go for harmonics up to some
>>> serious number.
>>>
>>> Can  anyone offer some advice as to algorithms ( number of cycles for
>>> such a deep notch ) and even better, a readily available eval board upon
>>> which it could be set up ? Remember I only need to 'hear' audio band, so
>>> 44.1 or 48 kHz sampling should be OK esp given the oversampling ADCs
>>> today.
>> A sharp filter for just one frequency is very easy. One ore more
>> biquad sections (5 multiplies & adds per biquad) are sufficient. That
>> doesn't take a lot of processing power. A cheap & simple ARM
>> microcontroller will do.
>>
>> Still, you should be aware of phase changes near the filter
>> frequencies.
> 
> Of course.
> 
>> I'm quite sure this will alter the sound.
> 
> I'm not interested in the 'sound' of the mains other than to see disturbances
> on it in the audio band.

Why not null out the 50 & 100 Hz components roughly with an analogue 
filter and then look at the rest of them. Chances are at least some of 
the clicks and pops are coming from zero crossing lamp controllers, CFL 
and other switch mode loads. Fridges, oil boiler and aircon motors seem 
to have the nastiest startup transients.
> 
> 
>> However I have to go along with Tim. Filtering 50Hz harmonics is not
>> going to help. The plops and clicks you mention are not a multiples of
>> 50Hz.
> 
> That's why I want to eliminate the 50 , 100 , 150 Hz etc so I can see what
> they ARE.

It might be easier to grab long chunks of the waveform with the 50 & 100 
Hz components only crudely nulled out and then use an FFT mask IFT type 
post processing solution to remove your remaining unwanted fundamentals. 
You only need to save the buffer when a click is heard. Something that 
is sharp in the time domain will be extended and spread out in the 
frequency domain. Clicks and pops should still be visible in the FFT 
even with some uncancelled fundamental.

I'd be more inclined to monitor the buildings 3 phase mains input power 
in realtime and look for contemporaneous sudden changes in the reported 
power usage just after a spike/pop/glitch is heard.
> 
>> These are just random spikes on the mains. If these spikes end
>> up in your audio circuitry, then you most likely have a ground loop or
>> another ground related problem somewhere. It means that the current
>> from the spike shares a return path with your audio signal.
> 
> Trust me, my colleague and I know all about ground loops, technical earths
> etc and have even completely Faraday caged several studios.
> 
> I do not believe it has anything to do with grounds on the basis of what I've
> seen.
> 
> What I'd really like to know is just where I can find info on doing what I
> wanted to do, i.e. perform sharp notch filters with a narrowish bandwidth. I
> do know what I'm doing in terms of trying to analyse the problem, I just need
> some help with the DSP.

I presume you have already tried copper/mu-metal/copper sheets above and 
below to prevent ingress of stray magnetic fields.

Regards,
Martin Brown

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message 
news:4A14B45B.7CDCFC35@hotmail.com...
>I am proposing to engage on a project regarding mains voltage 'purity'
> (and absence of ) with regard to audible clicks and pops in high-end
> professional and hi-fi audio equipment.
>
> Typical EMC filters operate in the RF band and are threfore no use to
> filter audio 'in band' noise that can travel through transformer
> interwinding capacitance etc.
>
> I have found some of the TI INA series that will with suitable
> preconditioning, tolerate mains voltages and give excellent common-mode
> etc rejection. So assembling a 'preamp' front end should be no problem.
>
> What I will need to do however is to filter all the mains frequencies
> and harmonics to a very large degree.
>
> I imagine I would need for example to null 50 Hz +/- 2 Hz to ~ -100dB. I
> have done only a little DSP ( I can't see it happening with analogue
> filters ) and I don't even know where to begin with such a severe filter
> without affecting the pass-band. Same will go for harmonics up to some
> serious number.
>
> Can  anyone offer some advice as to algorithms ( number of cycles for
> such a deep notch ) and even better, a readily available eval board upon
> which it could be set up ? Remember I only need to 'hear' audio band, so
> 44.1 or 48 kHz sampling should be OK esp given the oversampling ADCs
> today.
>
> Many thanks,    Graham

 Wouldn't it be easer to get a Digital CRO that can record/digitize the AC 
waveform --> Tranfer the data to a PC and post process Cro or FFT the 
waveform

Joe 

On Thu, 21 May 2009 02:54:36 +0100, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

>I am proposing to engage on a project regarding mains voltage 'purity'
>(and absence of ) with regard to audible clicks and pops in high-end
>professional and hi-fi audio equipment.

[...]

>I imagine I would need for example to null 50 Hz +/- 2 Hz to ~ -100dB. I
>have done only a little DSP ( I can't see it happening with analogue
>filters ) and I don't even know where to begin with such a severe filter
>without affecting the pass-band. Same will go for harmonics up to some
>serious number.

It looks to me like you're trying to do something similar to the old
method for determining harmonic distortion -- inject a pure sine wave,
filter the output with a notch filter at exactly the sine wave
frequency, and see what's left.  In your case, since you can't control
the input sine, an adaptive comb filter might be a better choice.  

The trouble with doing this by filtering, though, is that the
transient anomalies are also convolved with the filter impulse
response, so you cannot observe them directly.  Ideally you'd like to
be able to generate a model of the "clean" mains waveform and SUBTRACT
that from the actual waveform, instead of filtering.  Creation of that
waveform model moves you into the realm of system identification.

Whatever the case, it will need to be adaptive so that it can follow
normal slow variations in the mains voltage and frequency.

Greg

Jan Panteltje wrote:

> < snip>
> I clearly remember the first C class we had, and after that meeting was over, I went
> over to the instructor and asked him:
> "Where is the input and output in C?".
> He answered: "There is no such thing in C'."
> So I replied: "But then I cannot do anything with it, in embedded I need to do I/O".
> He then said: "But you can use in line asm to make your own out and in routines"....
> Now that was a relief :-)

Hence inc stdio.h presumably ?

Graham

In comp.dsp Jan Panteltje <pNaonStpealmtje@yahoo.com> wrote:
> Dear Rabit:
> http://panteltje.com/panteltje/xpequ/humfilter-0.1.tgz
> 
> Actually it is just an interface I wrote to the code of somebody else,
> the original was at http://www.abelian.demon.co.uk/humfilt/
> but no longer seems to respond...

It's moved to  http://abelian.org/humfilt/ ;)

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message 
news:4A14B45B.7CDCFC35@hotmail.com...
>I am proposing to engage on a project regarding mains voltage 'purity'
> (and absence of ) with regard to audible clicks and pops in high-end
> professional and hi-fi audio equipment.
>
> Typical EMC filters operate in the RF band and are threfore no use to
> filter audio 'in band' noise that can travel through transformer
> interwinding capacitance etc.
>
> I have found some of the TI INA series that will with suitable
> preconditioning, tolerate mains voltages and give excellent common-mode
> etc rejection. So assembling a 'preamp' front end should be no problem.
>
> What I will need to do however is to filter all the mains frequencies
> and harmonics to a very large degree.
>
> I imagine I would need for example to null 50 Hz +/- 2 Hz to ~ -100dB. I
> have done only a little DSP ( I can't see it happening with analogue
> filters ) and I don't even know where to begin with such a severe filter
> without affecting the pass-band. Same will go for harmonics up to some
> serious number.
>
> Can  anyone offer some advice as to algorithms ( number of cycles for
> such a deep notch ) and even better, a readily available eval board upon
> which it could be set up ? Remember I only need to 'hear' audio band, so
> 44.1 or 48 kHz sampling should be OK esp given the oversampling ADCs
> today.
>
> Many thanks,    Graham


You might find Julius Smith's work of interest: 
http://ccrma.stanford.edu/~jos/filters/

It seems the challenge is to create a comb filter with notches much sharper 
than can be achieved with a simple delay and addition.  Maybe the answer is 
a number of separate single-notch filters that can be made to track the 
supply frequency.

As for development kits, some are available (e.g. Analog Devices SHARC, from 
Farnell) but at a price greater than a PC nowadays so there may be some 
merit in doing the whole thing in C/C++ or Synthmaker on a PC if an adequate 
audio interface is to hand.  Especially if there is no intention of 
manufacturing later on.

Chris

Eeyore wrote:

> What I will need to do however is to filter all the mains frequencies
> and harmonics to a very large degree.
> 
> I imagine I would need for example to null 50 Hz +/- 2 Hz to ~ -100dB. I
> have done only a little DSP ( I can't see it happening with analogue
> filters ) and I don't even know where to begin with such a severe filter
> without affecting the pass-band. Same will go for harmonics up to some
> serious number.

The multiple notch filter is simple enough, however it will create the 
audible artifacts, and it won't do much help against the power interference.

> Can  anyone offer some advice as to algorithms ( number of cycles for
> such a deep notch )

Short answer: that won't work.

> and even better, a readily available eval board upon
> which it could be set up ?

Use a PC with a sound card.

> Remember I only need to 'hear' audio band, so
> 44.1 or 48 kHz sampling should be OK esp given the oversampling ADCs
> today.

In the broadcasting equipment, they used to inject the AC frequency and 
its harmonics into the audio to cancel out the power interference. The 
phases and amplitudes were adjusted for maximum rejection. That helped 
to some extent, however the power interference is rather nonlinear and 
nonstationary, which makes the problem difficult and non-trivial. So you 
shouldn't expect the miraculous improvement anyway.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

Nils wrote:

> After reading the discussion I wonder:
>
> Couldn't you simply connect a transformer to the mains, add a resistor
> divider at the output to get the signal down and record the glitches?

My front end will do all of that to get the levels right etc. The thing is,
you don't seem to be able to see the glitches for the mains, we've already
been looking. They must be quite small, or it's getting in via another
route. If we knew the route it would be easy but this is the task, to find
what the susceptibility is in a 35 year old product.

If we had unrestricted access we could try one idea at a time but it won't
be like that so we need to be prepared for various eventualities.


> That way we could take a look at the data and see what happends on the
> mains.
>
> You're at a recording studio after all. Recording something shouldn't be
> much of a problem. :-)

They might object to losing their hard disk rack. We can record it on a
laptop of course but real time would keep the client happier.

Graham

Eeyore wrote:

> > And finally, if it's clicks and pops you're trying to eliminate, that
> > would seem to indicate a problem with transients on the line, which
> > aren't things that you're going to notch out.
>
> Yes it does seem to be audio in band transients and my colleague and I have
> several ideas how it's getting into the audio and have already explored in
> some depth but we need more specialist tools to find the exact path.

To add to that we don't know if it's voltage transients getting in through the
mains and PSU or via magnetic coupling from sloppilly routed wiring for example.

Graham

On Thu, 21 May 2009 11:16:37 +0100, Eeyore wrote:

> Tim Wescott wrote:
> 
>> On Thu, 21 May 2009 02:54:36 +0100, Eeyore wrote:
>>
>> > I am proposing to engage on a project regarding mains voltage
>> > 'purity' (and absence of ) with regard to audible clicks and pops in
>> > high-end professional and hi-fi audio equipment.
>> >
>> > Typical EMC filters operate in the RF band and are threfore no use to
>> > filter audio 'in band' noise that can travel through transformer
>> > interwinding capacitance etc.
>> >
>> > I have found some of the TI INA series that will with suitable
>> > preconditioning, tolerate mains voltages and give excellent
>> > common-mode etc rejection. So assembling a 'preamp' front end should
>> > be no problem.
>> >
>> > What I will need to do however is to filter all the mains frequencies
>> > and harmonics to a very large degree.
>> >
>> > I imagine I would need for example to null 50 Hz +/- 2 Hz to ~
>> > -100dB. I have done only a little DSP ( I can't see it happening with
>> > analogue filters ) and I don't even know where to begin with such a
>> > severe filter without affecting the pass-band. Same will go for
>> > harmonics up to some serious number.
>> >
>> > Can  anyone offer some advice as to algorithms ( number of cycles for
>> > such a deep notch ) and even better, a readily available eval board
>> > upon which it could be set up ? Remember I only need to 'hear' audio
>> > band, so 44.1 or 48 kHz sampling should be OK esp given the
>> > oversampling ADCs today.
>> >
>> > Many thanks,    Graham
>>
>> This sounds like an adventure into audiophoolery, which isn't what I'd
>> expect of you.
> 
> No it's not. It's come about as a requirement from a real recording
> studio.
> 
> 
>> What, exactly, are you planning on filtering, and what are you planning
>> on filtering it against?
> 
> That's what we need to find out. Where are the clicks and pops getting
> in. We can't randomly spend the client's cash trying this and that. It
> needs to be a scientific investigation.
> 
> 
>> I suppose that you could filter your power supply rail with a supply
>> that has infinite rejection at all the power line harmonics -- but it
>> seems that a good switcher followed by a good linear regulator for
>> clean up would pound the power-line stuff down by many tens of dB.
> 
> The power supply rail is generated inside the console in this case from
> a balanced AC power feed. NO changes are possible.
> 
> 
>> If you absolutely had to get it down further you could incorporate a
>> resonant element in the feedback of the linear regulator, arranged to
>> provide a good notch.  Doing this with a DSP may just make sense in
>> that case.
> 
> I want the DSP to analyse what's going into the console PSU so I can see
> what needs to be addressed and where.
> 
> 
>> Filtering anything else sounds like flat-out magic.
> 
> Fine, come round to S. London and listen for yourself.
> 
> 
>> And finally, if it's clicks and pops you're trying to eliminate, that
>> would seem to indicate a problem with transients on the line, which
>> aren't things that you're going to notch out.
> 
> Yes it does seem to be audio in band transients and my colleague and I
> have several ideas how it's getting into the audio and have already
> explored in some depth but we need more specialist tools to find the
> exact path.
> 
> Graham

I think I understand now.  So this is just a measurement application, you 
want to monitor the power line, eliminate all the predictable stuff, and 
just look at what's left?

_That_ should be doable.  You'll still see some of the powerline content 
as the line voltage sags and recovers, but who knows?  That may be 
important, too.

For a first cut I'd suggest averaging successive 1/10th second intervals 
of incoming data to build up an image of the power line voltage, then 
subtract that out of your incoming signal.  The averaging should probably 
be done with some forgetting factor for each point (i.e. low-pass filter 
each point).

For a second cut you'll want to do the same thing, only do a much better 
job of synchronizing to the power line frequency, since one of you will 
be off.

There's lots of places you can go from there.

And I'd be happy to come to S. London and take a listen.  But I'd expect 
to get paid for the trip, and I have a tin ear*, so maybe you don't 
really want me to come out.

* That's not entirely true.  I can hear fast anomalies, and I can hear 
when equipment isn't "quite right".  But I grew up on cheap radios, so 
hearing something subtle underneath the music isn't something I can 
easily do.

-- 
http://www.wescottdesign.com

Eeyore wrote:
> 
> Jerry Avins wrote:

   ...

>> How does mains noise get into the equipment?
> 
> That's part of the project. To find out. I suspect many different possibilities
> but we can't rebuild the equipment so we need to find out what it's suspectible
> too. Plus we expect to be tackling this problem for many types of equipment.
> 
> 
>> Power supplies are filtered
>>   and regulated, so any noise you experience must enter by another
>> route. You might look into ferro-resonant transformers. These are
>> primarily intended to regulate load voltage, but they also suppress
>> voltage spikes. http://www.elect-spec.com/trnsreg.htm has examples.
>>
>> A capacitive shield between primary and secondary of the power
>> transformer may be all you need. Isolation transformers are built that way.
> 
> Yup I know. An ultra-isolation transformer will be part of our 'toolkit' too.
> I've used them before.But we need to know what interference is on the AC line.

You're on the way, then. Have you analyzed the line's harmonic content? 
There's plenty of instrumentation that can do that. One problem is what 
I call "dilution". The troublesome signals are transient, and tend to be 
swamped by the rest. The spectrum of impulsive noise is rarely impressive.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

Martin Brown wrote:

 > Eeyore wrote:

   ...

>> I'm not interested in the 'sound' of the mains other than to see 
>> disturbances on it in the audio band.

:-)

> Why not null out the 50 & 100 Hz components roughly with an analogue 
> filter and then look at the rest of them. Chances are at least some of 
> the clicks and pops are coming from zero crossing lamp controllers, CFL 
> and other switch mode loads. Fridges, oil boiler and aircon motors seem 
> to have the nastiest startup transients.

Lamp controllers switch at least once per cycle, usually twice. I can 
understand buzzes from them, but not clicks and pops.

   ...

>> Trust me, my colleague and I know all about ground loops, technical 
>> earths etc and have even completely Faraday caged several studios.

Is it practical to move some equipment to other studios to see if the 
disturbance follows them?

>> I do not believe it has anything to do with grounds on the basis of 
>> what I've seen.
>>
>> What I'd really like to know is just where I can find info on doing 
>> what I wanted to do, i.e. perform sharp notch filters with
>> a narrowish bandwidth. I >> do know what I'm doing in terms of trying 
>> to analyse the problem, I just need some help with the DSP.

And we've been trying to psych out the problem for you; sorry. Some links:

The "online courses" at http://www.bores.com/ Chris Bore is based in 
England and he consults.

Find the appropriate chapters in http://www.dspguide.com/

There is a bibliography at http://www.dspguru.com/

You should be able to implement the filters on a general-use computer 
with a good sound card.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

On May 20, 6:54=A0pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:
> I am proposing to engage on a project regarding mains voltage 'purity'
> (and absence of ) with regard to audible clicks and pops in high-end
> professional and hi-fi audio equipment.
>
> Typical EMC filters operate in the RF band and are threfore no use to
> filter audio 'in band' noise that can travel through transformer
> interwinding capacitance etc.
>
> I have found some of the TI INA series that will with suitable
> preconditioning, tolerate mains voltages and give excellent common-mode
> etc rejection. So assembling a 'preamp' front end should be no problem.
>
> What I will need to do however is to filter all the mains frequencies
> and harmonics to a very large degree.
>
> I imagine I would need for example to null 50 Hz +/- 2 Hz to ~ -100dB. I
> have done only a little DSP ( I can't see it happening with analogue
> filters ) and I don't even know where to begin with such a severe filter
> without affecting the pass-band. Same will go for harmonics up to some
> serious number.
>
> Can =A0anyone offer some advice as to algorithms ( number of cycles for
> such a deep notch ) and even better, a readily available eval board upon
> which it could be set up ? Remember I only need to 'hear' audio band, so
> 44.1 or 48 kHz sampling should be OK esp given the oversampling ADCs
> today.
>
> Many thanks, =A0 =A0Graham

I'd be more inclined to sample the AC by phase locking to it. Then you
could easily create a comb filter to kill the power line fundamental
and harmonics. This implies that you should use a 48kHz sample rate.

I'm not sure you need any filtering prior to sampling given the
dynamic range of ADCs these days.If your spike is say 70dB down from
the carrier (60/50 Hz mains), I can't believe it be significant to the
power supply design.

Besides basic DSP filtering, you could use LMS to get rid of the
fundamental. I suppose you could then LMS for each harmonic.

On 2009-05-21, Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
>
> That's what we need to find out. Where are the clicks and pops getting in. We
> can't randomly spend the client's cash trying this and that. It needs to be a
> scientific investigation.

I've been working on a tool at work that looks for problems in digitally
filtered audio.  One thing that is very effective at finding "pops" is
a spectrogram.  Even a single-cycle discontinuity shows up as a big line
(assuming your inputs are one or two tone such as your power line).  And
you can look at the spectrogram much faster than you can listen to the
equivalent audio.  You can also display several sources simultaneously.

-- 
Ben Jackson AD7GD
<ben@ben.com>
http://www.ben.com/

Jerry Avins wrote:

> Eeyore wrote:
> > Jerry Avins wrote:
>
>    ...
>
> >> How does mains noise get into the equipment?
> >
> > That's part of the project. To find out. I suspect many different possibilities
> > but we can't rebuild the equipment so we need to find out what it's suspectible
> > too. Plus we expect to be tackling this problem for many types of equipment.
> >
> >
> >> Power supplies are filtered
> >>   and regulated, so any noise you experience must enter by another
> >> route. You might look into ferro-resonant transformers. These are
> >> primarily intended to regulate load voltage, but they also suppress
> >> voltage spikes. http://www.elect-spec.com/trnsreg.htm has examples.
> >>
> >> A capacitive shield between primary and secondary of the power
> >> transformer may be all you need. Isolation transformers are built that way.
> >
> > Yup I know. An ultra-isolation transformer will be part of our 'toolkit' too.
> > I've used them before.But we need to know what interference is on the AC line.
>
> You're on the way, then. Have you analyzed the line's harmonic content?
> There's plenty of instrumentation that can do that. One problem is what
> I call "dilution". The troublesome signals are transient, and tend to be
> swamped by the rest. The spectrum of impulsive noise is rarely impressive.

Well for example the equipment in this instance, an 'antique' EMI mixing desk
produces 'clicks' when certain other loads are swiched. Now that varied from an air
condition unit drawing some 120A at start-up ( that also dimmed the lighting
momentarily until we put that on another supply ) to common or garden area lighting
and an outdoor security light switching.

The fact that it doesn't always click indicates to me that the phase angle of the
supply when swiched is part of the problem which is why I've designed a zero-voltage
switching 'add-on' for use with light switches. I also suspect magnetic field
interference from 'loopy' wiring.

We can only tell by testing the various possibilities and to do that we're going to
need to make a certain amount of our own test instrumentation.

At another studio we found interference from railway signalling currents. The track
ran right behind the plot. An EMC company had passed the site OK because they only
measure from 150kHz up and not in the audio band. I have a recording of the signal
made a simple pickup loop.That studio, along with some others required a total
Faraday cage.

Graham

Tim Wescott wrote:

> Eeyore wrote:
> > Tim Wescott wrote:
> >> On Thu, 21 May 2009 02:54:36 +0100, Eeyore wrote:
> >>
> >> > I am proposing to engage on a project regarding mains voltage
> >> > 'purity' (and absence of ) with regard to audible clicks and pops in
> >> > high-end professional and hi-fi audio equipment.
> >> >
> >> > Typical EMC filters operate in the RF band and are threfore no use to
> >> > filter audio 'in band' noise that can travel through transformer
> >> > interwinding capacitance etc.
> >> >
> >> > I have found some of the TI INA series that will with suitable
> >> > preconditioning, tolerate mains voltages and give excellent
> >> > common-mode etc rejection. So assembling a 'preamp' front end should
> >> > be no problem.
> >> >
> >> > What I will need to do however is to filter all the mains frequencies
> >> > and harmonics to a very large degree.
> >> >
> >> > I imagine I would need for example to null 50 Hz +/- 2 Hz to ~
> >> > -100dB. I have done only a little DSP ( I can't see it happening with
> >> > analogue filters ) and I don't even know where to begin with such a
> >> > severe filter without affecting the pass-band. Same will go for
> >> > harmonics up to some serious number.
> >> >
> >> > Can  anyone offer some advice as to algorithms ( number of cycles for
> >> > such a deep notch ) and even better, a readily available eval board
> >> > upon which it could be set up ? Remember I only need to 'hear' audio
> >> > band, so 44.1 or 48 kHz sampling should be OK esp given the
> >> > oversampling ADCs today.
> >> >
> >> > Many thanks,    Graham
> >>
> >> This sounds like an adventure into audiophoolery, which isn't what I'd
> >> expect of you.
> >
> > No it's not. It's come about as a requirement from a real recording
> > studio.
> >
> >
> >> What, exactly, are you planning on filtering, and what are you planning
> >> on filtering it against?
> >
> > That's what we need to find out. Where are the clicks and pops getting
> > in. We can't randomly spend the client's cash trying this and that. It
> > needs to be a scientific investigation.
> >
> >
> >> I suppose that you could filter your power supply rail with a supply
> >> that has infinite rejection at all the power line harmonics -- but it
> >> seems that a good switcher followed by a good linear regulator for
> >> clean up would pound the power-line stuff down by many tens of dB.
> >
> > The power supply rail is generated inside the console in this case from
> > a balanced AC power feed. NO changes are possible.
> >
> >
> >> If you absolutely had to get it down further you could incorporate a
> >> resonant element in the feedback of the linear regulator, arranged to
> >> provide a good notch.  Doing this with a DSP may just make sense in
> >> that case.
> >
> > I want the DSP to analyse what's going into the console PSU so I can see
> > what needs to be addressed and where.
> >
> >
> >> Filtering anything else sounds like flat-out magic.
> >
> > Fine, come round to S. London and listen for yourself.
> >
> >
> >> And finally, if it's clicks and pops you're trying to eliminate, that
> >> would seem to indicate a problem with transients on the line, which
> >> aren't things that you're going to notch out.
> >
> > Yes it does seem to be audio in band transients and my colleague and I
> > have several ideas how it's getting into the audio and have already
> > explored in some depth but we need more specialist tools to find the
> > exact path.
> >
> > Graham
>
> I think I understand now.  So this is just a measurement application, you
> want to monitor the power line, eliminate all the predictable stuff, and
> just look at what's left?

You've got it exactly. The frond end will enable differential, common-mode and
line to earth measurements.


> _That_ should be doable.  You'll still see some of the powerline content
> as the line voltage sags and recovers, but who knows?  That may be
> important, too.

That'll be quite slow compared to the clicks which I expect to be in the
lowish to mid kHz range so should be readily discernible.


> For a first cut I'd suggest averaging successive 1/10th second intervals
> of incoming data to build up an image of the power line voltage, then
> subtract that out of your incoming signal.  The averaging should probably
> be done with some forgetting factor for each point (i.e. low-pass filter
> each point).

I was thinking of doing this in real time ( hence the +/- 2 Hz requirement of
the 50 Hz filter ). That's the standard short-term frequency variance allowed
in the UK although it's normally within 0.1 Hz.


> For a second cut you'll want to do the same thing, only do a much better
> job of synchronizing to the power line frequency, since one of you will
> be off.

Hence the tolerance band to avoid that problem. Remember we need to 'catch'
these glitches in real time ideally. I'd like to capture them on my
colleague's digital scope. We're also going to make an intentional
'interferer' ! Our budget does stretch to Schaffner EMC type kit.        ;~)


> There's lots of places you can go from there.
>
> And I'd be happy to come to S. London and take a listen.  But I'd expect
> to get paid for the trip, and I have a tin ear*, so maybe you don't
> really want me to come out.

How far away are you ? Even with a tin ear you can hear these clicks. I can do
rather better but that's another story ( I once found a slightly hummy 'wall
wart' in the back of a rack that none of my colleagues could locate ). That's
when you start tilting your head and using the ear's directivity, walking
around and so on. I was pleased I got that.


> * That's not entirely true.  I can hear fast anomalies, and I can hear
> when equipment isn't "quite right".  But I grew up on cheap radios, so
> hearing something subtle underneath the music isn't something I can
> easily do.

You can hear this when the console is silent, so no problem there.

BTW, if you did drop in, you'd see an impressive collection of platinum albums
in the entrance hall !

Graham

Ben Jackson wrote:

> On 2009-05-21, Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
> >
> > That's what we need to find out. Where are the clicks and pops getting in. We
> > can't randomly spend the client's cash trying this and that. It needs to be a
> > scientific investigation.
>
> I've been working on a tool at work that looks for problems in digitally
> filtered audio.  One thing that is very effective at finding "pops" is
> a spectrogram.  Even a single-cycle discontinuity shows up as a big line
> (assuming your inputs are one or two tone such as your power line).  And
> you can look at the spectrogram much faster than you can listen to the
> equivalent audio.  You can also display several sources simultaneously.

That sounds interesting. I've done something similar possibly about 20 yrs ago (
durability of the AES / EBU standard connection ). We slung some stuff together
that worked as a 'glitch capturer' on a digitised 19kHz tone after the receiver.
You'd see regular losses of several cycles.

Interestingly we found we could only eliminate glitches totally was by using an
ultra-isolation transformer. This was in a standard office environment before PCs
were quite as widespread as now. These were very early days of digital audio of
course and the receivers weren't what I hope they are now. No dedicated chips back
then.

I also also saw some stunning difference in jitter on the data. The Studer D820
digital multitrack had the stablest timebase and the Mitsubishi X-850 2 track
mastering machine was the worst by a factor of around 200 IIRC. Somewhere I
probably still have a faded copy of a printout of the report.

Tell me more about your tool. I know a company that might be interested. They
already make kit to analyse analogue and digital audio. You may know them. Prism
Sound. I was working for them when I did the above.

Graham

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

>
>At another studio we found interference from railway signalling currents. The track
>ran right behind the plot. An EMC company had passed the site OK because they only
>measure from 150kHz up and not in the audio band. I have a recording of the signal
>made a simple pickup loop.That studio, along with some others required a total
>Faraday cage.

This just makes me wonder: Are there digital microphones? Nowadays its
easy to build a digital output on a microphone, guitar pick-up, etc.

I'm also a bit surprised studio equipment turns out to be so
susceptible to electric interference. Ever tried to connect the whole
lot to an on-line UPS (AC->DC DC->AC)? That should get you a very
clean mains.

-- 
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
                     "If it doesn't fit, use a bigger hammer!"
--------------------------------------------------------------

Martin Brown wrote:

> Eeyore wrote:
> > Nico Coesel wrote:
> >> Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
> >>
> >>> I am proposing to engage on a project regarding mains voltage 'purity'
> >>> (and absence of ) with regard to audible clicks and pops in high-end
> >>> professional and hi-fi audio equipment.
> >>>
> >>> Typical EMC filters operate in the RF band and are threfore no use to
> >>> filter audio 'in band' noise that can travel through transformer
> >>> interwinding capacitance etc.
> >>>
> >>> I have found some of the TI INA series that will with suitable
> >>> preconditioning, tolerate mains voltages and give excellent common-mode
> >>> etc rejection. So assembling a 'preamp' front end should be no problem.
> >>>
> >>> What I will need to do however is to filter all the mains frequencies
> >>> and harmonics to a very large degree.
> >>>
> >>> I imagine I would need for example to null 50 Hz +/- 2 Hz to ~ -100dB. I
> >>> have done only a little DSP ( I can't see it happening with analogue
> >>> filters ) and I don't even know where to begin with such a severe filter
> >>> without affecting the pass-band. Same will go for harmonics up to some
> >>> serious number.
> >>>
> >>> Can  anyone offer some advice as to algorithms ( number of cycles for
> >>> such a deep notch ) and even better, a readily available eval board upon
> >>> which it could be set up ? Remember I only need to 'hear' audio band, so
> >>> 44.1 or 48 kHz sampling should be OK esp given the oversampling ADCs
> >>> today.
> >> A sharp filter for just one frequency is very easy. One ore more
> >> biquad sections (5 multiplies & adds per biquad) are sufficient. That
> >> doesn't take a lot of processing power. A cheap & simple ARM
> >> microcontroller will do.
> >>
> >> Still, you should be aware of phase changes near the filter
> >> frequencies.
> >
> > Of course.
> >
> >> I'm quite sure this will alter the sound.
> >
> > I'm not interested in the 'sound' of the mains other than to see disturbances
> > on it in the audio band.
>
> Why not null out the 50 & 100 Hz components roughly with an analogue
> filter and then look at the rest of them. Chances are at least some of
> the clicks and pops are coming from zero crossing lamp controllers, CFL
> and other switch mode loads. Fridges, oil boiler and aircon motors seem
> to have the nastiest startup transients.

I'd half though of that. Make sure you include 150 Hz btw, the worst on the line
and 250 tends to be pretty bad too from memory of previous spectral analyses.
However I'd rather go the whole hog because access to studios is relatively rare
and you don't want to go in half-assed.


> >> However I have to go along with Tim. Filtering 50Hz harmonics is not
> >> going to help. The plops and clicks you mention are not a multiples of
> >> 50Hz.
> >
> > That's why I want to eliminate the 50 , 100 , 150 Hz etc so I can see what
> > they ARE.
>
> It might be easier to grab long chunks of the waveform with the 50 & 100
> Hz components only crudely nulled out and then use an FFT mask IFT type
> post processing solution to remove your remaining unwanted fundamentals.

Not really helpful since we want to see it happening in real time in response to
specific events.


> You only need to save the buffer when a click is heard. Something that
> is sharp in the time domain will be extended and spread out in the
> frequency domain. Clicks and pops should still be visible in the FFT
> even with some uncancelled fundamental.

Sort of used that method for something else but this really is different.


> I'd be more inclined to monitor the buildings 3 phase mains input power
> in realtime and look for contemporaneous sudden changes in the reported
> power usage just after a spike/pop/glitch is heard.

It's dual single phase actually. They may even be on the same phase but go back to
the street separately.


> >> These are just random spikes on the mains. If these spikes end
> >> up in your audio circuitry, then you most likely have a ground loop or
> >> another ground related problem somewhere. It means that the current
> >> from the spike shares a return path with your audio signal.
> >
> > Trust me, my colleague and I know all about ground loops, technical earths
> > etc and have even completely Faraday caged several studios.
> >
> > I do not believe it has anything to do with grounds on the basis of what I've
> > seen.
> >
> > What I'd really like to know is just where I can find info on doing what I
> > wanted to do, i.e. perform sharp notch filters with a narrowish bandwidth. I
> > do know what I'm doing in terms of trying to analyse the problem, I just need
> > some help with the DSP.
>
> I presume you have already tried copper/mu-metal/copper sheets above and
> below to prevent ingress of stray magnetic fields.

Not possible. The studio is complete and not suited to modification. Sure, there's
lots of things you could do if you went back to the beginning. In another story I
could tell you how useless I found mu-metal in an ultra-critical mic amp but that's
a LONG story and I suspect relates to transformer winding methods.

Graham

Jerry Avins wrote:

> Martin Brown wrote:
>  > Eeyore wrote:
>    ...
>
> >> I'm not interested in the 'sound' of the mains other than to see
> >> disturbances on it in the audio band.
>
> :-)
>
> > Why not null out the 50 & 100 Hz components roughly with an analogue
> > filter and then look at the rest of them. Chances are at least some of
> > the clicks and pops are coming from zero crossing lamp controllers, CFL
> > and other switch mode loads. Fridges, oil boiler and aircon motors seem
> > to have the nastiest startup transients.
>
> Lamp controllers switch at least once per cycle, usually twice. I can
> understand buzzes from them, but not clicks and pops.

I reckon it's the peak inrush current of a standard switch and bulb causing
most of the trouble. I just received today a couple of Surgegard samples which
I plan to use in combination with zero-voltage ( and hence current for a
resistive load ) switching. I'm sure this alone will make a difference.


> >> Trust me, my colleague and I know all about ground loops, technical
> >> earths etc and have even completely Faraday caged several studios.
>
> Is it practical to move some equipment to other studios to see if the
> disturbance follows them?

No. It's just the one studio and control room and you should see the sheer
size of this stuff.

I'm going to test their technical earth next time we're there too.


> >> I do not believe it has anything to do with grounds on the basis of
> >> what I've seen.
> >>
> >> What I'd really like to know is just where I can find info on doing
> >> what I wanted to do, i.e. perform sharp notch filters with
> >> a narrowish bandwidth. I do know what I'm doing in terms of trying
> >> to analyse the problem, I just need some help with the DSP.
>
> And we've been trying to psych out the problem for you; sorry. Some links:

All help is gratefully received.


> The "online courses" at http://www.bores.com/ Chris Bore is based in
> England and he consults.
>
> Find the appropriate chapters in http://www.dspguide.com/
>
> There is a bibliography at http://www.dspguru.com/
>
> You should be able to implement the filters on a general-use computer
> with a good sound card.

Thanks for that idea. I'd missed that one.

Graham

Jan Panteltje wrote:

> On a sunny day (Thu, 21 May 2009 02:54:36 +0100) it happened Eeyore
> <rabbitsfriendsandrelations@hotmail.com> wrote
>
> >I am proposing to engage on a project regarding mains voltage 'purity'
> >(and absence of ) with regard to audible clicks and pops in high-end
> >professional and hi-fi audio equipment.
> >
> >Typical EMC filters operate in the RF band and are threfore no use to
> >filter audio 'in band' noise that can travel through transformer
> >interwinding capacitance etc.
> >
> >I have found some of the TI INA series that will with suitable
> >preconditioning, tolerate mains voltages and give excellent common-mode
> >etc rejection. So assembling a 'preamp' front end should be no problem.
> >
> >What I will need to do however is to filter all the mains frequencies
> >and harmonics to a very large degree.
> >
> >I imagine I would need for example to null 50 Hz +/- 2 Hz to ~ -100dB. I
> >have done only a little DSP ( I can't see it happening with analogue
> >filters ) and I don't even know where to begin with such a severe filter
> >without affecting the pass-band. Same will go for harmonics up to some
> >serious number.
> >
> >Can  anyone offer some advice as to algorithms ( number of cycles for
> >such a deep notch ) and even better, a readily available eval board upon
> >which it could be set up ? Remember I only need to 'hear' audio band, so
> >44.1 or 48 kHz sampling should be OK esp given the oversampling ADCs
> >today.
> >
> >Many thanks,    Graham
>
> Dear Rabit:
>  http://panteltje.com/panteltje/xpequ/humfilter-0.1.tgz

tgz is one of those compressed file types isn't it ? Linux style ?


> Actually it is just an interface I wrote to the code of somebody else,
> the original was at http://www.abelian.demon.co.uk/humfilt/
> but no longer seems to respond...
>
> It is pretty good rejection, but does affect the sound.
> C code, of coure.

Aarghhh. No C compiler. Long story. I was offered a job programming in C
about 25 yrs ago even though I didn't know it. I hated the syntax so much I
didn't take it. I'd probably have made a fortune and be a 'C guru' if I had
done back then.

Graham

Mirek wrote:

> In comp.dsp Jan Panteltje <pNaonStpealmtje@yahoo.com> wrote:
> > Dear Rabit:
> > http://panteltje.com/panteltje/xpequ/humfilter-0.1.tgz
> >
> > Actually it is just an interface I wrote to the code of somebody else,
> > the original was at http://www.abelian.demon.co.uk/humfilt/
> > but no longer seems to respond...
>
> It's moved to  http://abelian.org/humfilt/ ;)

Oh, thanks.

Graham

On a sunny day (Thu, 21 May 2009 20:29:55 +0100) it happened Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote in
<4A15ABB3.D3913DF7@hotmail.com>:

>> Dear Rabit:
>>  http://panteltje.com/panteltje/xpequ/humfilter-0.1.tgz
>
>tgz is one of those compressed file types isn't it ? Linux style ?

Yes.


>> Actually it is just an interface I wrote to the code of somebody else,
>> the original was at http://www.abelian.demon.co.uk/humfilt/
>> but no longer seems to respond...
>>
>> It is pretty good rejection, but does affect the sound.
>> C code, of coure.
>
>Aarghhh. No C compiler. Long story. I was offered a job programming in C
>about 25 yrs ago even though I didn't know it. I hated the syntax so much I
>didn't take it. I'd probably have made a fortune and be a 'C guru' if I had
>done back then.

Yes the syntax can be a bit shocking if you are used to school math.....

'==' stands for '=' and '!' for is not etc..
+= -=, but it works.

Make a fortune? LOL, there is a lot of competetion in programming.

First question that occurs to me is ? real time ? or not?

If you do NOT have to do this real-time, there are a lot more options
in terms of processing off-line on a PC, and you can implement non-causal
filters (or more accurately, filters that would require non-causality for
a real-time implementation) which give you much more control and options.

As one example of this, any filter kernel can be used for non-(phase muckup)
if you use it twice, filtering ONCE in FORWARD time direction and ONCE more
in BACKWARD time direction.  THat is easy in offline processing and impossible
in real time.

So, do you have to do this real-time? Or is off-line analysis acceptable?

Eeyore wrote:
> 
> Jerry Avins wrote:
> 
>> Eeyore wrote:
>>> Jerry Avins wrote:
>>    ...
>>
>>>> How does mains noise get into the equipment?
>>> That's part of the project. To find out. I suspect many different possibilities
>>> but we can't rebuild the equipment so we need to find out what it's suspectible
>>> too. Plus we expect to be tackling this problem for many types of equipment.
>>>
>>>
>>>> Power supplies are filtered
>>>>   and regulated, so any noise you experience must enter by another
>>>> route. You might look into ferro-resonant transformers. These are
>>>> primarily intended to regulate load voltage, but they also suppress
>>>> voltage spikes. http://www.elect-spec.com/trnsreg.htm has examples.
>>>>
>>>> A capacitive shield between primary and secondary of the power
>>>> transformer may be all you need. Isolation transformers are built that way.
>>> Yup I know. An ultra-isolation transformer will be part of our 'toolkit' too.
>>> I've used them before.But we need to know what interference is on the AC line.
>> You're on the way, then. Have you analyzed the line's harmonic content?
>> There's plenty of instrumentation that can do that. One problem is what
>> I call "dilution". The troublesome signals are transient, and tend to be
>> swamped by the rest. The spectrum of impulsive noise is rarely impressive.
> 
> Well for example the equipment in this instance, an 'antique' EMI mixing desk
> produces 'clicks' when certain other loads are swiched. Now that varied from an air
> condition unit drawing some 120A at start-up ( that also dimmed the lighting
> momentarily until we put that on another supply ) to common or garden area lighting
> and an outdoor security light switching.

I dealt with a similar problem a long time back by switching troublesome 
loads with zero-crossing triacs. In fact, I still have a converted power 
strip with an electronic switch in it. It's hard to do that with the 
outdoor lighting, but a ferroresonant transformer should isolate direct 
attack from that quarter. Those things can even ride out a missing cycle 
or two, so glitches are well suppressed.

> The fact that it doesn't always click indicates to me that the phase angle of the
> supply when swiched is part of the problem which is why I've designed a zero-voltage
> switching 'add-on' for use with light switches. I also suspect magnetic field
> interference from 'loopy' wiring.


> We can only tell by testing the various possibilities and to do that we're going to
> need to make a certain amount of our own test instrumentation.
> 
> At another studio we found interference from railway signalling currents. The track
> ran right behind the plot. An EMC company had passed the site OK because they only
> measure from 150kHz up and not in the audio band. I have a recording of the signal
> made a simple pickup loop. That studio, along with some others required a total
> Faraday cage.

I believe that it was the simplest -- and counting time, the most 
economical -- approach. There was probably another way.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

Eeyore wrote:
> 
> Jerry Avins wrote:
> 
>> Martin Brown wrote:
>>  > Eeyore wrote:
>>    ...
>>
>>>> I'm not interested in the 'sound' of the mains other than to see
>>>> disturbances on it in the audio band.
>> :-)
>>
>>> Why not null out the 50 & 100 Hz components roughly with an analogue
>>> filter and then look at the rest of them. Chances are at least some of
>>> the clicks and pops are coming from zero crossing lamp controllers, CFL
>>> and other switch mode loads. Fridges, oil boiler and aircon motors seem
>>> to have the nastiest startup transients.
>> Lamp controllers switch at least once per cycle, usually twice. I can
>> understand buzzes from them, but not clicks and pops.
> 
> I reckon it's the peak inrush current of a standard switch and bulb causing
> most of the trouble. I just received today a couple of Surgegard samples which
> I plan to use in combination with zero-voltage ( and hence current for a
> resistive load ) switching. I'm sure this alone will make a difference.

Zero voltage switching is zero current also for an inductive load. Not 
in the steady state, of course, but at the instant of turn-on. Of 
course, SCR and triac switches always turn off at zero current.

>>>> Trust me, my colleague and I know all about ground loops, technical
>>>> earths etc and have even completely Faraday caged several studios.
>> Is it practical to move some equipment to other studios to see if the
>> disturbance follows them?
> 
> No. It's just the one studio and control room and you should see the sheer
> size of this stuff.
> 
> I'm going to test their technical earth next time we're there too.
> 
> 
>>>> I do not believe it has anything to do with grounds on the basis of
>>>> what I've seen.
>>>>
>>>> What I'd really like to know is just where I can find info on doing
>>>> what I wanted to do, i.e. perform sharp notch filters with
>>>> a narrowish bandwidth. I do know what I'm doing in terms of trying
>>>> to analyse the problem, I just need some help with the DSP.
>> And we've been trying to psych out the problem for you; sorry. Some links:
> 
> All help is gratefully received.
> 
> 
>> The "online courses" at http://www.bores.com/ Chris Bore is based in
>> England and he consults.
>>
>> Find the appropriate chapters in http://www.dspguide.com/
>>
>> There is a bibliography at http://www.dspguru.com/
>>
>> You should be able to implement the filters on a general-use computer
>> with a good sound card.
> 
> Thanks for that idea. I'd missed that one.

At your frequencies, you can also implement -- better yet, download -- 
an oscilloscope and spectrum analyzer. Ask if you need links. Somebody 
here must know them.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

Jan Panteltje wrote:
> On a sunny day (Thu, 21 May 2009 20:29:55 +0100) it happened Eeyore
> <rabbitsfriendsandrelations@hotmail.com> wrote in
> <4A15ABB3.D3913DF7@hotmail.com>:
> 
>>> Dear Rabit:
>>>  http://panteltje.com/panteltje/xpequ/humfilter-0.1.tgz
>> tgz is one of those compressed file types isn't it ? Linux style ?
> 
> Yes.
> 
> 
>>> Actually it is just an interface I wrote to the code of somebody else,
>>> the original was at http://www.abelian.demon.co.uk/humfilt/
>>> but no longer seems to respond...
>>>
>>> It is pretty good rejection, but does affect the sound.
>>> C code, of coure.
>> Aarghhh. No C compiler. Long story. I was offered a job programming in C
>> about 25 yrs ago even though I didn't know it. I hated the syntax so much I
>> didn't take it. I'd probably have made a fortune and be a 'C guru' if I had
>> done back then.
> 
> Yes the syntax can be a bit shocking if you are used to school math.....
> 
> '==' stands for '=' and '!' for is not etc..
> += -=, but it works.
> 
> Make a fortune? LOL, there is a lot of competetion in programming.

Personally, I like Forth for most things I do.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

"Joe G (Home)" wrote:

> "Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote
>
> >I am proposing to engage on a project regarding mains voltage 'purity'
> > (and absence of ) with regard to audible clicks and pops in high-end
> > professional and hi-fi audio equipment.
> >
> > Typical EMC filters operate in the RF band and are threfore no use to
> > filter audio 'in band' noise that can travel through transformer
> > interwinding capacitance etc.
> >
> > I have found some of the TI INA series that will with suitable
> > preconditioning, tolerate mains voltages and give excellent common-mode
> > etc rejection. So assembling a 'preamp' front end should be no problem.
> >
> > What I will need to do however is to filter all the mains frequencies
> > and harmonics to a very large degree.
> >
> > I imagine I would need for example to null 50 Hz +/- 2 Hz to ~ -100dB. I
> > have done only a little DSP ( I can't see it happening with analogue
> > filters ) and I don't even know where to begin with such a severe filter
> > without affecting the pass-band. Same will go for harmonics up to some
> > serious number.
> >
> > Can  anyone offer some advice as to algorithms ( number of cycles for
> > such a deep notch ) and even better, a readily available eval board upon
> > which it could be set up ? Remember I only need to 'hear' audio band, so
> > 44.1 or 48 kHz sampling should be OK esp given the oversampling ADCs
> > today.
>
>
>  Wouldn't it be easer to get a Digital CRO that can record/digitize the AC
> waveform --> Tranfer the data to a PC and post process Cro or FFT the
> waveform

We're not that wealthy ( the job's not going to pay for it ) and besides I'd
like to see it real-time. I'm not convinced the resolution of a scope ADC
would be adequate either.

Graham

christofire wrote:

> "Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote
>
> >I am proposing to engage on a project regarding mains voltage 'purity'
> > (and absence of ) with regard to audible clicks and pops in high-end
> > professional and hi-fi audio equipment.
> >
> > Typical EMC filters operate in the RF band and are threfore no use to
> > filter audio 'in band' noise that can travel through transformer
> > interwinding capacitance etc.
> >
> > I have found some of the TI INA series that will with suitable
> > preconditioning, tolerate mains voltages and give excellent common-mode
> > etc rejection. So assembling a 'preamp' front end should be no problem.
> >
> > What I will need to do however is to filter all the mains frequencies
> > and harmonics to a very large degree.
> >
> > I imagine I would need for example to null 50 Hz +/- 2 Hz to ~ -100dB. I
> > have done only a little DSP ( I can't see it happening with analogue
> > filters ) and I don't even know where to begin with such a severe filter
> > without affecting the pass-band. Same will go for harmonics up to some
> > serious number.
> >
> > Can  anyone offer some advice as to algorithms ( number of cycles for
> > such a deep notch ) and even better, a readily available eval board upon
> > which it could be set up ? Remember I only need to 'hear' audio band, so
> > 44.1 or 48 kHz sampling should be OK esp given the oversampling ADCs
> > today.
> >
> > Many thanks,    Graham
>
> You might find Julius Smith's work of interest:
> http://ccrma.stanford.edu/~jos/filters/
>
> It seems the challenge is to create a comb filter with notches much sharper
> than can be achieved with a simple delay and addition.  Maybe the answer is
> a number of separate single-notch filters that can be made to track the
> supply frequency.

Tracking would be neat for sure but as a first option the +/- 4% on notch width
would do, most likely less. I like the idea though, then you can calculate the
coefficiencts from the tracked fundamental.


> As for development kits, some are available (e.g. Analog Devices SHARC, from
> Farnell) but at a price greater than a PC nowadays so there may be some
> merit in doing the whole thing in C/C++ or Synthmaker on a PC if an adequate
> audio interface is to hand.  Especially if there is no intention of
> manufacturing later on.

Yes, good idea. No plan to manufacture, at least not now. All I want initially
is something 'quick and dirty' but that does the job acceptable well.

There are eval boards around for various DSPs. Implementing this on an
inexpensive one would save a lot of time and effort.

Graham

Vladimir Vassilevsky wrote:

> Eeyore wrote:
>
> > What I will need to do however is to filter all the mains frequencies
> > and harmonics to a very large degree.
> >
> > I imagine I would need for example to null 50 Hz +/- 2 Hz to ~ -100dB. I
> > have done only a little DSP ( I can't see it happening with analogue
> > filters ) and I don't even know where to begin with such a severe filter
> > without affecting the pass-band. Same will go for harmonics up to some
> > serious number.
>
> The multiple notch filter is simple enough, however it will create the
> audible artifacts, and it won't do much help against the power interference.

It's the interference I want to discriminate from the power line fundamental and
harmonics and see in real time.


> > Can  anyone offer some advice as to algorithms ( number of cycles for
> > such a deep notch )
>
> Short answer: that won't work.

Not sure what you mean there. I've only a small experience of DSP filtering you
see, although I've done some moderately complex audio reverb processing.


> > and even better, a readily available eval board upon
> > which it could be set up ?
>
> Use a PC with a sound card.

Could do, although I'd prefer a 'one box' solution.


> > Remember I only need to 'hear' audio band, so
> > 44.1 or 48 kHz sampling should be OK esp given the oversampling ADCs
> > today.
>
> In the broadcasting equipment, they used to inject the AC frequency and
> its harmonics into the audio to cancel out the power interference.

That must have been ages ago or specific to broadcast. Besides anything that
moves over about 200m gets digitised and goes up fibre optic these days. Not a
technique ever used in recording studios I've ever seen and that goes back a
bit.


> The phases and amplitudes were adjusted for maximum rejection. That helped
> to some extent, however the power interference is rather nonlinear and
> nonstationary, which makes the problem difficult and non-trivial.

Exactly.


> So you shouldn't expect the miraculous improvement anyway.

I think you may have misinterpreted what I'm seeking. Tim Wescott's second post
hit the nail on the head.

Graham

"miso@sushi.com" wrote:

> Eeyore <rabbitsfriendsandrelati...@hotmail.com> wrote:
>
> > I am proposing to engage on a project regarding mains voltage 'purity'
> > (and absence of ) with regard to audible clicks and pops in high-end
> > professional and hi-fi audio equipment.
> >
> > Typical EMC filters operate in the RF band and are threfore no use to
> > filter audio 'in band' noise that can travel through transformer
> > interwinding capacitance etc.
> >
> > I have found some of the TI INA series that will with suitable
> > preconditioning, tolerate mains voltages and give excellent common-mode
> > etc rejection. So assembling a 'preamp' front end should be no problem.
> >
> > What I will need to do however is to filter all the mains frequencies
> > and harmonics to a very large degree.
> >
> > I imagine I would need for example to null 50 Hz +/- 2 Hz to ~ -100dB. I
> > have done only a little DSP ( I can't see it happening with analogue
> > filters ) and I don't even know where to begin with such a severe filter
> > without affecting the pass-band. Same will go for harmonics up to some
> > serious number.
> >
> > Can  anyone offer some advice as to algorithms ( number of cycles for
> > such a deep notch ) and even better, a readily available eval board upon
> > which it could be set up ? Remember I only need to 'hear' audio band, so
> > 44.1 or 48 kHz sampling should be OK esp given the oversampling ADCs
> > today.
>
> I'd be more inclined to sample the AC by phase locking to it.

Yes, sampling the mains fundamental would be neat. I don't think you'd even
need to be phase locked for simple notch filters.


> Then you could easily create a comb filter to kill the power line
> fundamental
> and harmonics. This implies that you should use a 48kHz sample rate.

Readily available.


> I'm not sure you need any filtering prior to sampling given the
> dynamic range of ADCs these days.

Agreed. Just a simple first order at some high frequency for luck probably.


> If your spike is say 70dB down from the carrier (60/50 Hz mains), I can't
> believe it be significant to the
> power supply design.

I wouldn't make ANY assumptions of that nature with today's high SNR audio !
I've seen some astonishing things.


> Besides basic DSP filtering, you could use LMS to get rid of the
> fundamental. I suppose you could then LMS for each harmonic.

Hadn't thought of LMS. Not looked at it in ages actually. You mean the
off-the-shelf package ? A bit pricey IIRC.

Graham

Nico Coesel wrote:

> Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
>
> >At another studio we found interference from railway signalling currents. The track
> >ran right behind the plot. An EMC company had passed the site OK because they only
> >measure from 150kHz up and not in the audio band. I have a recording of the signal
> >made a simple pickup loop.That studio, along with some others required a total
> >Faraday cage.
>
> This just makes me wonder: Are there digital microphones? Nowadays its
> easy to build a digital output on a microphone, guitar pick-up, etc.

I think there may be some that claim to be but it's far from mainstream so far.


> I'm also a bit surprised studio equipment turns out to be so
> susceptible to electric interference.

LMAO ! Excuse my mirth ! I've seen kit built even in recent times that breaks every rule
of good practice for EMC. You just wouldn't believe it. You get these 'one man bands'
touting their 'golden ears' genius and I've looked inside some of their kit and seen the
problem ( typically hum loops )  instantly. Basic fundamental stupid errors.


> Ever tried to connect the whole
> lot to an on-line UPS (AC->DC DC->AC)? That should get you a very
> clean mains.

I've had good results with an ultra-isolation transformer in the past which will kill
any power line transient but I'm far from sure that's the whole problem.

Graham

Jan Panteltje wrote:

> it happened Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote
>
> >> Dear Rabit:
> >>  http://panteltje.com/panteltje/xpequ/humfilter-0.1.tgz
> >
> >tgz is one of those compressed file types isn't it ? Linux style ?
>
> Yes.
>
> >> Actually it is just an interface I wrote to the code of somebody else,
> >> the original was at http://www.abelian.demon.co.uk/humfilt/
> >> but no longer seems to respond...
> >>
> >> It is pretty good rejection, but does affect the sound.
> >> C code, of coure.
> >
> >Aarghhh. No C compiler. Long story. I was offered a job programming in C
> >about 25 yrs ago even though I didn't know it. I hated the syntax so much I
> >didn't take it. I'd probably have made a fortune and be a 'C guru' if I had
> >done back then.
>
> Yes the syntax can be a bit shocking if you are used to school math.....
>
> '==' stands for '=' and '!' for is not etc..
> += -=, but it works.

I think I preferred even Fortran's GT. GE. etc !


> Make a fortune? LOL, there is a lot of competetion in programming.

Not in C 25 years ago. But that's another story.

Graham

Jerry Avins wrote:

> Eeyore wrote:
> > Jerry Avins wrote:
> >> Eeyore wrote:
> >>> Jerry Avins wrote:
> >>    ...
> >>
> >>>> How does mains noise get into the equipment?
> >>> That's part of the project. To find out. I suspect many different possibilities
> >>> but we can't rebuild the equipment so we need to find out what it's suspectible
> >>> too. Plus we expect to be tackling this problem for many types of equipment.
> >>>
> >>>
> >>>> Power supplies are filtered
> >>>>   and regulated, so any noise you experience must enter by another
> >>>> route. You might look into ferro-resonant transformers. These are
> >>>> primarily intended to regulate load voltage, but they also suppress
> >>>> voltage spikes. http://www.elect-spec.com/trnsreg.htm has examples.
> >>>>
> >>>> A capacitive shield between primary and secondary of the power
> >>>> transformer may be all you need. Isolation transformers are built that way.
> >>> Yup I know. An ultra-isolation transformer will be part of our 'toolkit' too.
> >>> I've used them before.But we need to know what interference is on the AC line.
> >> You're on the way, then. Have you analyzed the line's harmonic content?
> >> There's plenty of instrumentation that can do that. One problem is what
> >> I call "dilution". The troublesome signals are transient, and tend to be
> >> swamped by the rest. The spectrum of impulsive noise is rarely impressive.
> >
> > Well for example the equipment in this instance, an 'antique' EMI mixing desk
> > produces 'clicks' when certain other loads are swiched. Now that varied from an air
> > condition unit drawing some 120A at start-up ( that also dimmed the lighting
> > momentarily until we put that on another supply ) to common or garden area lighting
> > and an outdoor security light switching.
>
> I dealt with a similar problem a long time back by switching troublesome
> loads with zero-crossing triacs.

Guess what design is on the desk right now !        ;~)


> In fact, I still have a converted power
> strip with an electronic switch in it. It's hard to do that with the
> outdoor lighting, but a ferroresonant transformer should isolate direct
> attack from that quarter. Those things can even ride out a missing cycle
> or two, so glitches are well suppressed.

Yes, but a big investment if it doesn't fix it. I've asked a UK manufacturer if they'll
loan one for a week or two but it didn't sound promising.


> > The fact that it doesn't always click indicates to me that the phase angle of the
> > supply when swiched is part of the problem which is why I've designed a zero-voltage
> > switching 'add-on' for use with light switches. I also suspect magnetic field
> > interference from 'loopy' wiring.
>
> > We can only tell by testing the various possibilities and to do that we're going to
> > need to make a certain amount of our own test instrumentation.
> >
> > At another studio we found interference from railway signalling currents. The track
> > ran right behind the plot. An EMC company had passed the site OK because they only
> > measure from 150kHz up and not in the audio band. I have a recording of the signal
> > made a simple pickup loop. That studio, along with some others required a total
> > Faraday cage.
>
> I believe that it was the simplest -- and counting time, the most
> economical -- approach. There was probably another way.

Possibly, but the Faraday cage worked beautifully. We did a site follow-up and it wasn't
actually all that expensive either. I think it came to � 30-40k. After all, it was just
sheet upon sheet mostly of 2mm thick mild steel screwed to the interior shell of the
building and welded together. They had some clever method for dealing with windows too.

Graham

Jerry Avins wrote:

> Eeyore wrote:
> > Jerry Avins wrote:
> >> Martin Brown wrote:
> >>  > Eeyore wrote:
> >>    ...
> >>
> >>>> I'm not interested in the 'sound' of the mains other than to see
> >>>> disturbances on it in the audio band.
> >> :-)
> >>
> >>> Why not null out the 50 & 100 Hz components roughly with an analogue
> >>> filter and then look at the rest of them. Chances are at least some of
> >>> the clicks and pops are coming from zero crossing lamp controllers, CFL
> >>> and other switch mode loads. Fridges, oil boiler and aircon motors seem
> >>> to have the nastiest startup transients.
> >> Lamp controllers switch at least once per cycle, usually twice. I can
> >> understand buzzes from them, but not clicks and pops.
> >
> > I reckon it's the peak inrush current of a standard switch and bulb causing
> > most of the trouble. I just received today a couple of Surgegard samples which
> > I plan to use in combination with zero-voltage ( and hence current for a
> > resistive load ) switching. I'm sure this alone will make a difference.
>
> Zero voltage switching is zero current also for an inductive load. Not
> in the steady state, of course, but at the instant of turn-on. Of
> course, SCR and triac switches always turn off at zero current.

Of course. Double benefit. Nearly forgot that. And 'loopy wiring' will have
inductance.


> >>>> Trust me, my colleague and I know all about ground loops, technical
> >>>> earths etc and have even completely Faraday caged several studios.
> >> Is it practical to move some equipment to other studios to see if the
> >> disturbance follows them?
> >
> > No. It's just the one studio and control room and you should see the sheer
> > size of this stuff.
> >
> > I'm going to test their technical earth next time we're there too.
> >
> >
> >>>> I do not believe it has anything to do with grounds on the basis of
> >>>> what I've seen.
> >>>>
> >>>> What I'd really like to know is just where I can find info on doing
> >>>> what I wanted to do, i.e. perform sharp notch filters with
> >>>> a narrowish bandwidth. I do know what I'm doing in terms of trying
> >>>> to analyse the problem, I just need some help with the DSP.
> >> And we've been trying to psych out the problem for you; sorry. Some links:
> >
> > All help is gratefully received.
> >
> >
> >> The "online courses" at http://www.bores.com/ Chris Bore is based in
> >> England and he consults.
> >>
> >> Find the appropriate chapters in http://www.dspguide.com/
> >>
> >> There is a bibliography at http://www.dspguru.com/
> >>
> >> You should be able to implement the filters on a general-use computer
> >> with a good sound card.
> >
> > Thanks for that idea. I'd missed that one.
>
> At your frequencies, you can also implement -- better yet, download --
> an oscilloscope and spectrum analyzer. Ask if you need links. Somebody
> here must know them.

It's more the inverse of a spectrum analyser I need. Somthing that 'ignores' the
mains and its harmonics and only registers disturbances.

I'm glad I got into this EMC lark ( almost by accident along with product safety )
over 20 yrs ago. I can see how some people just don't 'get it'. I think too many
people dismiss it as 'boring' but it's actually very clever if your mind is open to
the ideas involved.

Graham

Jerry Avins wrote:

> Jan Panteltje wrote:
> > On a sunny day (Thu, 21 May 2009 20:29:55 +0100) it happened Eeyore
> > <rabbitsfriendsandrelations@hotmail.com> wrote in
> >
> >>> Dear Rabit:
> >>>  http://panteltje.com/panteltje/xpequ/humfilter-0.1.tgz
> >> tgz is one of those compressed file types isn't it ? Linux style ?
> >
> > Yes.
> >
> >
> >>> Actually it is just an interface I wrote to the code of somebody else,
> >>> the original was at http://www.abelian.demon.co.uk/humfilt/
> >>> but no longer seems to respond...
> >>>
> >>> It is pretty good rejection, but does affect the sound.
> >>> C code, of coure.
> >> Aarghhh. No C compiler. Long story. I was offered a job programming in C
> >> about 25 yrs ago even though I didn't know it. I hated the syntax so much I
> >> didn't take it. I'd probably have made a fortune and be a 'C guru' if I had
> >> done back then.
> >
> > Yes the syntax can be a bit shocking if you are used to school math.....
> >
> > '==' stands for '=' and '!' for is not etc..
> > += -=, but it works.
> >
> > Make a fortune? LOL, there is a lot of competetion in programming.
>
> Personally, I like Forth for most things I do.

It may be old but it's good. PL/M (51) is my Forte. There are so many diverse 8051
family derivatives there's rarely one that won't fit the job and I find writing it
a total breeze. I even released a product for manufacture with 'beta' code,
expecting *someone* would be able to break it. A year went by and it was still
being shipped with the same beta code. Seemed a shame to change it, so that's how
it stayed.

I did once write an embedded application in Pascal  ( MX Pascal ? ) to run on a
Z80. Don't even ask why. Or mention the EMC problems. That machine ( designed by
another firm of 'consultants' ) still makes me laugh to this day. Pascal's OK too.
We fixed it and the client was overjoyed.

Graham

"Kevin G. Rhoads" wrote:

> First question that occurs to me is ? real time ? or not?

I would like it in real-time, so we can initiatate an event and see the result
simultaneously.


> If you do NOT have to do this real-time, there are a lot more options
> in terms of processing off-line on a PC, and you can implement non-causal
> filters (or more accurately, filters that would require non-causality for
> a real-time implementation) which give you much more control and options.

That would be so much less helpful that I think I'd rule it out.


> As one example of this, any filter kernel can be used for non-(phase muckup)
> if you use it twice, filtering ONCE in FORWARD time direction and ONCE more
> in BACKWARD time direction.  THat is easy in offline processing and impossible
> in real time.

What's the advantage ?


> So, do you have to do this real-time? Or is off-line analysis acceptable?

As you see above, real-time is very much preferred.

Graham

On a sunny day (Thu, 21 May 2009 22:13:04 +0100) it happened Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote in
<4A15C3E0.298E7BC4@hotmail.com>:

>> >Aarghhh. No C compiler. Long story. I was offered a job programming in C
>> >about 25 yrs ago even though I didn't know it. I hated the syntax so much I
>> >didn't take it. I'd probably have made a fortune and be a 'C guru' if I had
>> >done back then.

>
>> Make a fortune? LOL, there is a lot of competition in programming.
>
>Not in C 25 years ago. But that's another story.

I learned C, lemme see, in 1984-1987 or there about.
So 25 years ago, had been in contact with Unix already in 79, but not C programming.
At that time I was developing embedded on 8051 / 8047 IIRC, and looking
at other micros too.
I was the hardware developer, and the software department, those worked in those times
a lot with x86 asm, all on real IBM PCs, were a bit eh lemme say: overloaded?
by having to learn Yet An Other asm language.
The big boss, who was asm freak himself, then decided that we all should learn C.
So we had C classes.
I clearly remember the first C class we had, and after that meeting was over, I went
over to the instructor and asked him:
"Where is the input and output in C?".
He answered: "There is no such thing in C'."
So I replied: "But then I cannot do anything with it, in embedded I need to do I/O".
He then said: "But you can use in line asm to make your own out and in routines"....
Now that was a relief :-)

But competitive environment, we had Z80 too...

On May 21, 2:04=A0pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:
> "m...@sushi.com" wrote:
> > Eeyore <rabbitsfriendsandrelati...@hotmail.com> wrote:
>
> > > I am proposing to engage on a project regarding mains voltage 'purity=
'
> > > (and absence of ) with regard to audible clicks and pops in high-end
> > > professional and hi-fi audio equipment.
>
> > > Typical EMC filters operate in the RF band and are threfore no use to
> > > filter audio 'in band' noise that can travel through transformer
> > > interwinding capacitance etc.
>
> > > I have found some of the TI INA series that will with suitable
> > > preconditioning, tolerate mains voltages and give excellent common-mo=
de
> > > etc rejection. So assembling a 'preamp' front end should be no proble=
m.
>
> > > What I will need to do however is to filter all the mains frequencies
> > > and harmonics to a very large degree.
>
> > > I imagine I would need for example to null 50 Hz +/- 2 Hz to ~ -100dB=
.. I
> > > have done only a little DSP ( I can't see it happening with analogue
> > > filters ) and I don't even know where to begin with such a severe fil=
ter
> > > without affecting the pass-band. Same will go for harmonics up to som=
e
> > > serious number.
>
> > > Can =A0anyone offer some advice as to algorithms ( number of cycles f=
or
> > > such a deep notch ) and even better, a readily available eval board u=
pon
> > > which it could be set up ? Remember I only need to 'hear' audio band,=
 so
> > > 44.1 or 48 kHz sampling should be OK esp given the oversampling ADCs
> > > today.
>
> > I'd be more inclined to sample the AC by phase locking to it.
>
> Yes, sampling the mains fundamental would be neat. I don't think you'd ev=
en
> need to be phase locked for simple notch filters.
>
> > Then you could easily create a comb filter to kill the power line
> > fundamental
> > and harmonics. This implies that you should use a 48kHz sample rate.
>
> Readily available.
>
> > I'm not sure you need any filtering prior to sampling given the
> > dynamic range of ADCs these days.
>
> Agreed. Just a simple first order at some high frequency for luck probabl=
y.
>
> > If your spike is say 70dB down from the carrier (60/50 Hz mains), I can=
't
> > believe it be significant to the
> > power supply design.
>
> I wouldn't make ANY assumptions of that nature with today's high SNR audi=
o !
> I've seen some astonishing things.
>
> > Besides basic DSP filtering, you could use LMS to get rid of the
> > fundamental. I suppose you could then LMS for each harmonic.
>
> Hadn't thought of LMS. Not looked at it in ages actually. You mean the
> off-the-shelf package ? A bit pricey IIRC.
>
> Graham

I programmed the LMS fit. For the fundamental, you just phase unwrap
the sampled signal (presumably a sine) with an arcsin. The phase
versus time plot should be series of points that would ideally be a
straight line. If you fit a line to these points using LMS, the slope
will indicate the LMS best fit to frequency. At the time, that was all
I needed to do. But later I hacked a bit by creating a perfect sine
wave using this LMS derived slope. I don't recall how I did the
amplitude fit, but I think I didn't do LMS, but just ran some
optimizer to vary the amplitude to make the difference between samples
and the fitted sine wave go to a minimum. This is not a rigorous
solution to the problem, but probably valid. Note I did this a few
decades ago, so none of this is perfectly fresh in my mind, but the
technique as I recall it is sound.

As a hardware person, I think the phase locked sampling and comb
filter would be the way to go. You probably would have to come up with
a VXCO for the phase locked source. I hate all this windowing stuff.
Synchronous sampling is much cleaner.

"Jerry Avins":


> Zero voltage switching is zero current also for an inductive load. Not in 
> the steady state, of course, but at the instant of turn-on.

**  However, a zero volt AC switch applied to a mains transformer invariably 
results in a maximum size inrush current surge.

 The surge current peak will arrive about half a cycle after switch on.

 In the case of toroidal transformers, current peaks can be over 100 amps.


......   Phil

Eeyore wrote:
> 
> Martin Brown wrote:
> 
>> Why not null out the 50 & 100 Hz components roughly with an analogue
>> filter and then look at the rest of them. Chances are at least some of
>> the clicks and pops are coming from zero crossing lamp controllers, CFL
>> and other switch mode loads. Fridges, oil boiler and aircon motors seem
>> to have the nastiest startup transients.
> 
> I'd half though of that. Make sure you include 150 Hz btw, the worst on the line
> and 250 tends to be pretty bad too from memory of previous spectral analyses.
> However I'd rather go the whole hog because access to studios is relatively rare
> and you don't want to go in half-assed.

If you capture the raw data as acquired you have an insurance policy.
> 
>>>> However I have to go along with Tim. Filtering 50Hz harmonics is not
>>>> going to help. The plops and clicks you mention are not a multiples of
>>>> 50Hz.
>>> That's why I want to eliminate the 50 , 100 , 150 Hz etc so I can see what
>>> they ARE.
>> It might be easier to grab long chunks of the waveform with the 50 & 100
>> Hz components only crudely nulled out and then use an FFT mask IFT type
>> post processing solution to remove your remaining unwanted fundamentals.
> 
> Not really helpful since we want to see it happening in real time in response to
> specific events.

You could process it on an ordinary PC fast enough to look like realtime 
to a human. All you want to ensure is that the signal spike you are 
looking for will be adequately digitised so removing all the major 
components to within a couple of volts ought to be good enough.

FFTs are very resilient if you signal average the power spectrum.

>> You only need to save the buffer when a click is heard. Something that
>> is sharp in the time domain will be extended and spread out in the
>> frequency domain. Clicks and pops should still be visible in the FFT
>> even with some uncancelled fundamental.
> 
> Sort of used that method for something else but this really is different.

What are you hoping to learn from this experiment?

Wouldn't a transient detector be much simpler to implement and almost as 
good?

>> I'd be more inclined to monitor the buildings 3 phase mains input power
>> in realtime and look for contemporaneous sudden changes in the reported
>> power usage just after a spike/pop/glitch is heard.
> 
> It's dual single phase actually. They may even be on the same phase but go back to
> the street separately.

But total power in is easy to monitor and the signature of the sorts of 
heavyweight aircon kit likely to cause trouble should be unmissable. 
Thinking about it I'd be inclined to take along a bunch of wireless 
webcams pointed at the most likely suspects and record them timestamped 
with the other stuff.

>>>> These are just random spikes on the mains. If these spikes end
>>>> up in your audio circuitry, then you most likely have a ground loop or
>>>> another ground related problem somewhere. It means that the current
>>>> from the spike shares a return path with your audio signal.

>>> Trust me, my colleague and I know all about ground loops, technical earths
>>> etc and have even completely Faraday caged several studios.
>>>
>>> I do not believe it has anything to do with grounds on the basis of what I've
>>> seen.
>>>
>>> What I'd really like to know is just where I can find info on doing what I
>>> wanted to do, i.e. perform sharp notch filters with a narrowish bandwidth. I
>>> do know what I'm doing in terms of trying to analyse the problem, I just need
>>> some help with the DSP.

>> I presume you have already tried copper/mu-metal/copper sheets above and
>> below to prevent ingress of stray magnetic fields.
> 
> Not possible. The studio is complete and not suited to modification. Sure, there's
> lots of things you could do if you went back to the beginning. In another story I
> could tell you how useless I found mu-metal in an ultra-critical mic amp but that's
> a LONG story and I suspect relates to transformer winding methods.


Mu-metal on its own isn't all that good. It has high magnetic 
susceptibility but isn't that good a conductor. It needs a layer of very 
good conductor on top to generate field cancelling eddy currents. 
Bacofoil will do at a pinch.

Regards,
Martin Brown

After reading the discussion I wonder:

Couldn't you simply connect a transformer to the mains, add a resistor 
divider at the output to get the signal down and record the glitches?

That way we could take a look at the data and see what happends on the 
mains.

You're at a recording studio after all. Recording something shouldn't be 
much of a problem. :-)

Cheers,
   Nils

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

>
>
>Jan Panteltje wrote:
>
>> < snip>
>> I clearly remember the first C class we had, and after that meeting was over, I went
>> over to the instructor and asked him:
>> "Where is the input and output in C?".
>> He answered: "There is no such thing in C'."
>> So I replied: "But then I cannot do anything with it, in embedded I need to do I/O".
>> He then said: "But you can use in line asm to make your own out and in routines"....
>> Now that was a relief :-)
>
>Hence inc stdio.h presumably ?

He was probably working on an Intelish platform with seperate memory
and I/O spaces.

-- 
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
                     "If it doesn't fit, use a bigger hammer!"
--------------------------------------------------------------

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

>
>
>Nils wrote:
>
>> After reading the discussion I wonder:
>>
>> Couldn't you simply connect a transformer to the mains, add a resistor
>> divider at the output to get the signal down and record the glitches?
>
>My front end will do all of that to get the levels right etc. The thing is,
>you don't seem to be able to see the glitches for the mains, we've already
>been looking. They must be quite small, or it's getting in via another

Get a proper digital scope. Many scopes lower their samplerates so you
don't see short glitches. Lecroy is bad when it comes to this kind of
behaviour. What you need it peak detect.

-- 
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
                     "If it doesn't fit, use a bigger hammer!"
--------------------------------------------------------------

Eeyore wrote:

> Nils wrote:
>
> > After reading the discussion I wonder:
> >
> > Couldn't you simply connect a transformer to the mains, add a resistor
> > divider at the output to get the signal down and record the glitches?
>
> My front end will do all of that to get the levels right etc. The thing is,
> you don't seem to be able to see the glitches for the mains

I should add to that, just looking on a scope trace or even using a HEME power
quality analyser which seems to be targeted at other problems like longer term
dips and surges.

Graham

Nico Coesel wrote:

> Eeyore wrote:
> >Nils wrote:
> >
> >> After reading the discussion I wonder:
> >>
> >> Couldn't you simply connect a transformer to the mains, add a resistor
> >> divider at the output to get the signal down and record the glitches?
> >
> >My front end will do all of that to get the levels right etc. The thing is,
> >you don't seem to be able to see the glitches for the mains, we've already
> >been looking. They must be quite small, or it's getting in via another
>
> Get a proper digital scope. Many scopes lower their samplerates so you
> don't see short glitches. Lecroy is bad when it comes to this kind of
> behaviour. What you need it peak detect.

I agree but it's beyond our budget for this alone. By making dedicated kit of
our own, designed specifically for this kind of job alone we can avoid that
problem.

Graham

"miso@sushi.com" wrote:

> Eeyore <rabbitsfriendsandrelati...@hotmail.com> wrote:
> > Nils wrote:
> > > After reading the discussion I wonder:
> >
> > > Couldn't you simply connect a transformer to the mains, add a resistor
> > > divider at the output to get the signal down and record the glitches?
> >
> > My front end will do all of that to get the levels right etc. The thing is,
> > you don't seem to be able to see the glitches for the mains, we've already
> > been looking. They must be quite small, or it's getting in via another
> > route. If we knew the route it would be easy but this is the task, to find
> > what the susceptibility is in a 35 year old product.
> >
> > If we had unrestricted access we could try one idea at a time but it won't
> > be like that so we need to be prepared for various eventualities.
> >
> > > That way we could take a look at the data and see what happends on the
> > > mains.
> >
> > > You're at a recording studio after all. Recording something shouldn't be
> > > much of a problem. :-)
> >
> > They might object to losing their hard disk rack. We can record it on a
> > laptop of course but real time would keep the client happier.
>
> Have you researched Dranetz gear?
> http://www.dranetz-bmi.com/

I know their kind of stuff and Schaffner EMC too but this work won't pay for
that.

Graham

Nico Coesel wrote:

> Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
> >Jan Panteltje wrote:
> >
> >> < snip>
> >> I clearly remember the first C class we had, and after that meeting was over, I went
> >> over to the instructor and asked him:
> >> "Where is the input and output in C?".
> >> He answered: "There is no such thing in C'."
> >> So I replied: "But then I cannot do anything with it, in embedded I need to do I/O".
> >> He then said: "But you can use in line asm to make your own out and in routines"....
> >> Now that was a relief :-)
> >
> >Hence inc stdio.h presumably ?
>
> He was probably working on an Intelish platform with seperate memory
> and I/O spaces.

That's what I like about PL/M. It automatically points to the right space according to the
command and register etc definition file.

Graham

Nico Coesel wrote:

> Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
> >"miso@sushi.com" wrote:
> >> Eeyore <rabbitsfriendsandrelati...@hotmail.com> wrote:
> >> > Nils wrote:
> >> > > After reading the discussion I wonder:
> >> >
> >> > > Couldn't you simply connect a transformer to the mains, add a resistor
> >> > > divider at the output to get the signal down and record the glitches?
> >> >
> >> > My front end will do all of that to get the levels right etc. The thing is,
> >> > you don't seem to be able to see the glitches for the mains, we've already
> >> > been looking. They must be quite small, or it's getting in via another
> >> > route. If we knew the route it would be easy but this is the task, to find
> >> > what the susceptibility is in a 35 year old product.
> >> >
> >> > If we had unrestricted access we could try one idea at a time but it won't
> >> > be like that so we need to be prepared for various eventualities.
> >> >
> >> > > That way we could take a look at the data and see what happends on the
> >> > > mains.
> >> >
> >> > > You're at a recording studio after all. Recording something shouldn't be
> >> > > much of a problem. :-)
> >> >
> >> > They might object to losing their hard disk rack. We can record it on a
> >> > laptop of course but real time would keep the client happier.
> >>
> >> Have you researched Dranetz gear?
> >> http://www.dranetz-bmi.com/
> >
> >I know their kind of stuff and Schaffner EMC too but this work won't pay for
> >that.
>
> I get a feeling you have a lot of time for this project, but not a
> large budget to work with?

Pretty much. I'm helping out a colleague who hasn't the funds for the expensive gear
and can't design 'clever' electronics himself. The potential bonus for me is  that
if we get it right we could be experts in the field. Ever lower noise levels mean
more and more of this is surfacing.


> I would get a high quality USB audio interface.

I think he has something similar using firewire but there was something odd about
it, would have to ask him again.


> Put a front end together for measuring line voltages and
> have it record for a few days at the highest resolution/sampling
> frequency. Cooledit is a very good program for analyzing the data.
>
> I think this route is faster than try to get going with DSP
> algorithms.

Could be done but I was very interested in the DSP route because of that real time
processing advantage.

Jan's idea interested me for example.
http://panteltje.com/panteltje/xpequ/humfilter-0.1.tgz
http://abelian.org/humfilt/

Aside from not having a Linux box to run it on right now.

Graham

Tim Wescott wrote:

> This sounds like an adventure into audiophoolery, which isn't what I'd
> expect of you.
>
> What, exactly, are you planning on filtering

We expect some treatment of the mains supply ( maybe audio 'in band filtering'
or an isolation transformer ) , possibly re-wiring mains and signal cabling to
avoid large loops and zero-crossing certain loads.


> and what are you planning on filtering it against?

What appear to be audio in band transients superimposed on the mains or
entering the audio chain by inductive coupling. Unlikely to be capacitive
coupling into the audio directly.


> I suppose that you could filter your power supply rail with a supply that
> has infinite rejection at all the power line harmonics --

Or maybe just a very low pass filter.

Incidentally, from our findings here we may be able to sell products into the
'audiophool' market that REALLY WORK ! They had an 'audiophool filter' on the
premises from the grand fools Russ Andrews and their �800 'mains conditioner'
connects the live and neutral in directly to the outlet sockets with some
largish capacitors in parallel ! Some 'conditioner'.

http://www.russandrews.com/product.asp?lookup=1&region=UK&currency=GBP&pf_id=1101&customer_id=PAA2306051009397CVMURDTGYWSUBNOB

I note you're left-pondian btw, so a visit to S london would be a little
excessive.      :~)

Graham

Nico Coesel wrote:

> However I have to go along with Tim. Filtering 50Hz harmonics is not
> going to help. The plops and clicks you mention are not a multiples of
> 50Hz. These are just random spikes on the mains. If these spikes end
> up in your audio circuitry, then you most likely have a ground loop or
> another ground related problem somewhere. It means that the current
> from the spike shares a return path with your audio signal.

Ah, I think you misundestood that I intended to filter the wanted audio. Not
at all.

What I want to find is the mode of propagation of the mains borne transients
into the equipment by eliminating the power line frequency and harmonics from
tests we can run on the supplies and even the free-field. Which just gave me
an idea.

Graham

Jon Kirwan wrote:

> Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
>
> >I am proposing to engage on a project regarding mains voltage 'purity'
> >(and absence of ) with regard to audible clicks and pops in high-end
> >professional and hi-fi audio equipment.
> ><snip>
>
> Hi, Graham.  A thought crossed my mind and it leads to some questions.
>
> (1)  I think you mention elsewhere "to find what the susceptibility is
> in a 35 year old product."  Is this something that has started more
> recently, then?  Or has it been going on for a long time and they are
> only now noticing or otherwise deciding to deal with it?

They may be being a little coy about this. I found evidence of obvious
previous attempts to clean up the mains using 'audiophool grade' components
such as ....
http://www.russandrews.com/product.asp?lookup=1&region=UK&currency=GBP&pf_id=1101&customer_id=PAA2306051009397CVMURDTGYWSUBNOB

It always pays to sniff about.

My colleague was there primarily though to remove the effect of inrush
current from the a/c which dimmed the lighting momentarily. By
re-connecting the mains more suitably to to 2 separate supplies he got rid
of that problem but the studio operators said he'd introduced this new one.
Maybe he made it more susceptible but the existence of the above
'conditioner' makes me suspect there was always something there.

Incidentally, in the end they took his advice and installed a new
low-inrush aircon unit ! Duh !

And we also found the supposed 'balanced' 25-0-25 AC supply to the console
wasn't balanced. It was 66-106-156 as a result of a suitable named
'Tinkertek' replacement AC supply. So people have been fiddling before. I
managed to rewire it to make it properly 25-0-25 and that did seem to help
a bit.

The original 'PSU' used a CVT to provide the balanced AC which would have
provided high transient isolation but due to age was no longer regulating
properly and the output voltage was low causing regulator drop-out so
couldn't be re-evaluated.

Recall that the console takes AC and DC is derived in each channel
cassette. We don't know if the transformers in these cassettes have an ES
screen.


> (2)  Who else (or what other activities) occupy the building?

Nothing other than domestic.


> (3)  On what time scale do these events occur?

For example when lights are switched. So the frequency of occurence could
be anything.


> I had a situation, years ago, where a dental office moved into the
> building on a different floor.  Turns out, they had an x-ray machine
> and they used it, on occasion.  When they did, I'd get nice, narrow kV
> spikes back on the AC line that fed us.  There was another weird one
> where a nearby research facility (150' away) would turn on some of
> their equipment and we'd see our ground (relative to theirs) jump 7kV.
> The copper communications line was a mess during that transition.
>
> In other words, have you also checked out what's new, who else is
> doing what, nearby?

Good tip but it's in a residential area and the source of the transients is
internal to the building and its wiring..

Graham

Eeyore wrote:

> Jon Kirwan wrote:
>
> > (3)  On what time scale do these events occur?
>
> For example when lights are switched. So the frequency of occurence could
> be anything.

Just remembered that the air extractor in the 'loo' caused an audible transient too. That was fixed by replacement with another
model ( reason for the difference not known ).

Graham

On May 21, 6:51=A0am, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:
> Nils wrote:
> > After reading the discussion I wonder:
>
> > Couldn't you simply connect a transformer to the mains, add a resistor
> > divider at the output to get the signal down and record the glitches?
>
> My front end will do all of that to get the levels right etc. The thing i=
s,
> you don't seem to be able to see the glitches for the mains, we've alread=
y
> been looking. They must be quite small, or it's getting in via another
> route. If we knew the route it would be easy but this is the task, to fin=
d
> what the susceptibility is in a 35 year old product.
>
> If we had unrestricted access we could try one idea at a time but it won'=
t
> be like that so we need to be prepared for various eventualities.
>
> > That way we could take a look at the data and see what happends on the
> > mains.
>
> > You're at a recording studio after all. Recording something shouldn't b=
e
> > much of a problem. :-)
>
> They might object to losing their hard disk rack. We can record it on a
> laptop of course but real time would keep the client happier.
>
> Graham

Have you researched Dranetz gear?
http://www.dranetz-bmi.com/

On Thu, 21 May 2009 02:54:36 +0100, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

>I am proposing to engage on a project regarding mains voltage 'purity'
>(and absence of ) with regard to audible clicks and pops in high-end
>professional and hi-fi audio equipment.
><snip>

Hi, Graham.  A thought crossed my mind and it leads to some questions.

(1)  I think you mention elsewhere "to find what the susceptibility is
in a 35 year old product."  Is this something that has started more
recently, then?  Or has it been going on for a long time and they are
only now noticing or otherwise deciding to deal with it?

(2)  Who else (or what other activities) occupy the building?

(3)  On what time scale do these events occur?

I had a situation, years ago, where a dental office moved into the
building on a different floor.  Turns out, they had an x-ray machine
and they used it, on occasion.  When they did, I'd get nice, narrow kV
spikes back on the AC line that fed us.  There was another weird one
where a nearby research facility (150' away) would turn on some of
their equipment and we'd see our ground (relative to theirs) jump 7kV.
The copper communications line was a mess during that transition.

In other words, have you also checked out what's new, who else is
doing what, nearby?

Jon

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

>
>
>"miso@sushi.com" wrote:
>
>> Eeyore <rabbitsfriendsandrelati...@hotmail.com> wrote:
>> > Nils wrote:
>> > > After reading the discussion I wonder:
>> >
>> > > Couldn't you simply connect a transformer to the mains, add a resistor
>> > > divider at the output to get the signal down and record the glitches?
>> >
>> > My front end will do all of that to get the levels right etc. The thing is,
>> > you don't seem to be able to see the glitches for the mains, we've already
>> > been looking. They must be quite small, or it's getting in via another
>> > route. If we knew the route it would be easy but this is the task, to find
>> > what the susceptibility is in a 35 year old product.
>> >
>> > If we had unrestricted access we could try one idea at a time but it won't
>> > be like that so we need to be prepared for various eventualities.
>> >
>> > > That way we could take a look at the data and see what happends on the
>> > > mains.
>> >
>> > > You're at a recording studio after all. Recording something shouldn't be
>> > > much of a problem. :-)
>> >
>> > They might object to losing their hard disk rack. We can record it on a
>> > laptop of course but real time would keep the client happier.
>>
>> Have you researched Dranetz gear?
>> http://www.dranetz-bmi.com/
>
>I know their kind of stuff and Schaffner EMC too but this work won't pay for
>that.

I get a feeling you have a lot of time for this project, but not a
large budget to work with? I would get a high quality USB audio
interface. Put a front end together for measuring line voltages and
have it record for a few days at the highest resolution/sampling
frequency. Cooledit is a very good program for analyzing the data.

I think this route is faster than try to get going with DSP
algorithms.

-- 
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
                     "If it doesn't fit, use a bigger hammer!"
--------------------------------------------------------------

Eeyore a �crit :
> 
> Eeyore wrote:
> 
>> Jon Kirwan wrote:
>>
>>> (3)  On what time scale do these events occur?
>> For example when lights are switched. So the frequency of occurence could
>> be anything.
> 
> Just remembered that the air extractor in the 'loo' caused an audible transient too. That was fixed by replacement with another
> model ( reason for the difference not known ).
> 
> Graham
> 

Just make a self oscillating (battery+relay) EMI generator and take it 
all over the place. With a bit of chance you'll quickly find the 
sensitive loop(s).

-- 
Thanks,
Fred.

"Fred Bartoli"

>
> Just make a self oscillating (battery+relay) EMI generator and take it all 
> over the place. With a bit of chance you'll quickly find the sensitive 
> loop(s).


** The lying, stuffed cartoon character already knows exactly what the  " 
sensitive loop " in the room is.

Like some white elephant standing in the corner -  it's the antique EMI 
mixing desk  !

Basic audio fact:

A virtual earth mixing buss  IS  an induction loop receiver  !!

Common sense studio rule:

" No AC powered equipment is to be turned on off while recording is in 
progress. "


What a fucking crock of old shit the congenitally manic pommy charlatan is 
purveying now.

What a PITA scumbag.



.....   Phil

On May 22, 1:44=A0pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:
> Nico Coesel wrote:
> > Eeyore <rabbitsfriendsandrelati...@hotmail.com> wrote:
> > >"m...@sushi.com" wrote:
> > >> Eeyore <rabbitsfriendsandrelati...@hotmail.com> wrote:
> > >> > Nils wrote:
> > >> > > After reading the discussion I wonder:
>
> > >> > > Couldn't you simply connect a transformer to the mains, add a re=
sistor
> > >> > > divider at the output to get the signal down and record the glit=
ches?
>
> > >> > My front end will do all of that to get the levels right etc. The =
thing is,
> > >> > you don't seem to be able to see the glitches for the mains, we've=
 already
> > >> > been looking. They must be quite small, or it's getting in via ano=
ther
> > >> > route. If we knew the route it would be easy but this is the task,=
 to find
> > >> > what the susceptibility is in a 35 year old product.
>
> > >> > If we had unrestricted access we could try one idea at a time but =
it won't
> > >> > be like that so we need to be prepared for various eventualities.
>
> > >> > > That way we could take a look at the data and see what happends =
on the
> > >> > > mains.
>
> > >> > > You're at a recording studio after all. Recording something shou=
ldn't be
> > >> > > much of a problem. :-)
>
> > >> > They might object to losing their hard disk rack. We can record it=
 on a
> > >> > laptop of course but real time would keep the client happier.
>
> > >> Have you researched Dranetz gear?
> > >>http://www.dranetz-bmi.com/
>
> > >I know their kind of stuff and Schaffner EMC too but this work won't p=
ay for
> > >that.
>
> > I get a feeling you have a lot of time for this project, but not a
> > large budget to work with?
>
> Pretty much. I'm helping out a colleague who hasn't the funds for the exp=
ensive gear
> and can't design 'clever' electronics himself. The potential bonus for me=
 is =A0that
> if we get it right we could be experts in the field. Ever lower noise lev=
els mean
> more and more of this is surfacing.
>
> > I would get a high quality USB audio interface.
>
> I think he has something similar using firewire but there was something o=
dd about
> it, would have to ask him again.
>
> > Put a front end together for measuring line voltages and
> > have it record for a few days at the highest resolution/sampling
> > frequency. Cooledit is a very good program for analyzing the data.
>
> > I think this route is faster than try to get going with DSP
> > algorithms.
>
> Could be done but I was very interested in the DSP route because of that =
real time
> processing advantage.
>
> Jan's idea interested me for example.http://panteltje.com/panteltje/xpequ=
/humfilter-0.1.tgzhttp://abelian.org/humfilt/
>
> Aside from not having a Linux box to run it on right now.
>
> Graham

You can always dual boot a windows PC. The Suse installer is pretty
smart regarding not messing with the other operating systems. I can't
see NOT having a linux box handy since there is so much open source
engineering software that runs under Linux. Sound on linux is hit and
miss. The program you mention uses OSS, which I think these days is
emulated via ALSA. Doing anything other than standard CD rate audio
can be problematic since all the drivers are 3rd party written by
volunteers. My current favorite soundcard for Linux is the Diamond
XS71. Cheap, fine performance, and works in many flavors of Linux.
Suse will sniff it and set it up as a C-Media chipset card. This one
will fall back to 8 bits if need be, which yeah, sounds bad in theory,
but a lot of the older programs used the 8 bit mode for communications
demodulation.

With a bit more skill, you could set up a live CD version of Suse or
whatever Linux you chose. The issue then would be to create the
ramdisk so you could install the software. I'm suspecting that would
be difficult. I don't know if the live CDs even have the compilers
installed, let alone the libraries.

The comb filter will only be "perfect" if the line frequency and
sample clock are phased locked.

On May 25, 10:10=A0pm, "m...@sushi.com" <m...@sushi.com> wrote:

> You can always dual boot a windows PC.

It can be quite a challenge for a non Unix wizzard to start using
Linux,
especially command line tools like humfilter.
As humfitler is a a simple command line program,.
written in a simple C, and basically only
does wav file format input to wave file output,
it should be easily portable to DOS, and run in
a MSDOS window in for example XP.
Perhaps compile with the old djgpp compiler?
Several of my programs have been ported to DOS by people.
I am sure you can somehow send the wave output to a soundcard
even in MS software.

   Here are my thoughts after reading the whole thread (I DID learn C
22 years ago - didn't make me rich, but it paid a lot more than
cleaning toilets in recording studios, and probably even more than
designing pro audio equipment).

In sci.electronics.design and comp.dsp, On Thu, 21 May 2009 02:54:36
+0100, Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

>I am proposing to engage on a project regarding mains voltage 'purity'
>(and absence of ) with regard to audible clicks and pops in high-end
>professional and hi-fi audio equipment.
>
>Typical EMC filters operate in the RF band and are threfore no use to
>filter audio 'in band' noise that can travel through transformer
>interwinding capacitance etc.
>
>I have found some of the TI INA series that will with suitable
>preconditioning, tolerate mains voltages and give excellent common-mode
>etc rejection. So assembling a 'preamp' front end should be no problem.

   From what others posted, I'm thinking you might want to make
several of these, to also measure things like the neutral voltage and
the ground voltage (maybe referenced to your own ground stake you put
in the ground outside the window or door, on the opposite side of the
building where the main power comes in). Make these to withstand a
kilovolt or more on the inputs (use several series resistors in each
leg). That way you can see common-mode signals as well as
differential.

>
>What I will need to do however is to filter all the mains frequencies
>and harmonics to a very large degree.

   You say elsewhere you want to see the results in "real time." I
interpret that as "not having to wait 30 seconds for processing," that
a half-second or two seconds might be acceptable.

   Others have said it, but I also see this as a PC application. A USB
audio interface with four inputs should work (you probably want 24bit
samples - if USB can't do 48/24 and 4 channels, you then use a desktop
machine (or firewire, whatever), perhaps powered by a battery backup
to insure line isolation, with a 4=channel or 8-channel card). Three
inputs are for hot-to-neutral, neutral-to-your-ground,
ground-to-your-ground, and the forth is the balanced output (with
ground not connected!) of the mixer/console/UUT.

   You run this thing, and it samples data continuously. When the
mixer has an output (or when there's an anomalous output on any of the
other three inputs), the thing samples a few more cycles, then stops
and does the filtering (on data that's a few cycles long), and shows
the areas of interest, both with and without the 50/60Hz imposed on
the hot/neutral input.

   This puts all the algorithms in a PC which has plenty of DSP
horsepower thesedays, and also makes a good multichannel data
recorder. I'm thinking you (or someone who knows C and PC code
development) can get the Audacity source and modify it to do this (I
don't know of the legalities and such of using the code in a
commercial product, if you have to make the code you add open-source
or what).

   And you just might want to have more inputs to look at, such as the
main DC filtering caps of the console. This would show if the
transient occurs at a time when the rectifiers are conducting.

On Sat, 23 May 2009 01:25:25 +0100, Eeyore
<rabbitsfriendsandrelations@notmail.com> wrote:

>
>
>Eeyore wrote:
>
>> Jon Kirwan wrote:
>>
>> > (3)  On what time scale do these events occur?
>>
>> For example when lights are switched. So the frequency of occurence could
>> be anything.
>
>Just remembered that the air extractor in the 'loo' caused an audible transient too. That was fixed by replacement with another
>model ( reason for the difference not known ).

   Do you still have the old one? Will it make the same or similar
electrical noise if you just plug it in or unplug it from an outlet?
If not can you hook it back up to that same circuit and reproduce the
problem?  I'm thinking you really want to know the "reason for the
difference" in this case, or at least have an (extra) example of a
known-bad audible transient generator, to test how well any future fix
of the sound equipment works.

>
>Graham

Ben Bradley wrote:

> Eeyore <rabbitsfriendsandrelations@notmail.com> wrote:
> >Eeyore wrote:
> >> Jon Kirwan wrote:
> >>
> >> > (3)  On what time scale do these events occur?
> >>
> >> For example when lights are switched. So the frequency of occurence could
> >> be anything.
> >
> >Just remembered that the air extractor in the 'loo' caused an audible transient too. That was fixed by >replacement with another
> model ( reason for the difference not known ).
>
>    Do you still have the old one?

Yes, it's been retained.


> Will it make the same or similar electrical noise if you just plug it in or unplug it from an outlet?

Unknown at this time as another guy was working on the mains wiring.


> If not can you hook it back up to that same circuit and reproduce the
> problem?  I'm thinking you really want to know the "reason for the
> difference" in this case, or at least have an (extra) example of a
> known-bad audible transient generator, to test how well any future fix
> of the sound equipment works.

Agreed.

Graham

On May 25, 2:21=A0pm, pantel...@gmail.com wrote:
> On May 25, 10:10=A0pm, "m...@sushi.com" <m...@sushi.com> wrote:
>
> > You can always dual boot a windows PC.
>
> It can be quite a challenge for a non Unix wizzard to start using
> Linux,
> especially command line tools like humfilter.
> As humfitler is a a simple command line program,.
> written in a simple C, and basically only
> does wav file format input to wave file output,
> it should be easily portable to DOS, and run in
> a MSDOS window in for example XP.
> Perhaps compile with the old djgpp compiler?
> Several of my programs have been ported to DOS by people.
> I am sure you can somehow send the wave output to a soundcard
> even in MS software.

It's been my experience that it is easier to compile software under
Linux. The lack of compilers for windows is the issue.  I assume to
use the soundcard in windows, you need to use some windows API, and
the documentation or lack thereof can be frustrating.

While I'm not a programmer, I took a course in VB. Simple enough,
except when it came to the APIs. The didn't always work as expected.
Jan Axelmans (I think) serial book documented flag that were the
opposite of what was described.

On Fri, 22 May 2009 11:31:03 +0100, Martin Brown
<|||newspam|||@nezumi.demon.co.uk> wrote:

>Eeyore wrote:
>>=20
>> Martin Brown wrote:
>>=20
>>> Why not null out the 50 & 100 Hz components roughly with an analogue
>>> filter and then look at the rest of them. Chances are at least some =
of
>>> the clicks and pops are coming from zero crossing lamp controllers, =
CFL
>>> and other switch mode loads. Fridges, oil boiler and aircon motors =
seem
>>> to have the nastiest startup transients.
>>=20
>> I'd half though of that. Make sure you include 150 Hz btw, the worst =
on the line
>> and 250 tends to be pretty bad too from memory of previous spectral =
analyses.
>> However I'd rather go the whole hog because access to studios is =
relatively rare
>> and you don't want to go in half-assed.
>
>If you capture the raw data as acquired you have an insurance policy.
>>=20
>>>>> However I have to go along with Tim. Filtering 50Hz harmonics is =
not
>>>>> going to help. The plops and clicks you mention are not a multiples=
 of
>>>>> 50Hz.
>>>> That's why I want to eliminate the 50 , 100 , 150 Hz etc so I can =
see what
>>>> they ARE.
>>> It might be easier to grab long chunks of the waveform with the 50 & =
100
>>> Hz components only crudely nulled out and then use an FFT mask IFT =
type
>>> post processing solution to remove your remaining unwanted =
fundamentals.
>>=20
>> Not really helpful since we want to see it happening in real time in =
response to
>> specific events.
>
>You could process it on an ordinary PC fast enough to look like realtime=
=20
>to a human. All you want to ensure is that the signal spike you are=20
>looking for will be adequately digitised so removing all the major=20
>components to within a couple of volts ought to be good enough.
>
>FFTs are very resilient if you signal average the power spectrum.
>
>>> You only need to save the buffer when a click is heard. Something =
that
>>> is sharp in the time domain will be extended and spread out in the
>>> frequency domain. Clicks and pops should still be visible in the FFT
>>> even with some uncancelled fundamental.
>>=20
>> Sort of used that method for something else but this really is =
different.
>
>What are you hoping to learn from this experiment?
>
>Wouldn't a transient detector be much simpler to implement and almost as=
=20
>good?
>
>>> I'd be more inclined to monitor the buildings 3 phase mains input =
power
>>> in realtime and look for contemporaneous sudden changes in the =
reported
>>> power usage just after a spike/pop/glitch is heard.
>>=20
>> It's dual single phase actually. They may even be on the same phase =
but go back to
>> the street separately.
>
>But total power in is easy to monitor and the signature of the sorts of=20
>heavyweight aircon kit likely to cause trouble should be unmissable.=20
>Thinking about it I'd be inclined to take along a bunch of wireless=20
>webcams pointed at the most likely suspects and record them timestamped=20
>with the other stuff.
>
>>>>> These are just random spikes on the mains. If these spikes end
>>>>> up in your audio circuitry, then you most likely have a ground loop=
 or
>>>>> another ground related problem somewhere. It means that the current
>>>>> from the spike shares a return path with your audio signal.
>
>>>> Trust me, my colleague and I know all about ground loops, technical =
earths
>>>> etc and have even completely Faraday caged several studios.
>>>>
>>>> I do not believe it has anything to do with grounds on the basis of =
what I've
>>>> seen.
>>>>
>>>> What I'd really like to know is just where I can find info on doing =
what I
>>>> wanted to do, i.e. perform sharp notch filters with a narrowish =
bandwidth. I
>>>> do know what I'm doing in terms of trying to analyse the problem, I =
just need
>>>> some help with the DSP.
>
>>> I presume you have already tried copper/mu-metal/copper sheets above =
and
>>> below to prevent ingress of stray magnetic fields.
>>=20
>> Not possible. The studio is complete and not suited to modification. =
Sure, there's
>> lots of things you could do if you went back to the beginning. In =
another story I
>> could tell you how useless I found mu-metal in an ultra-critical mic =
amp but that's
>> a LONG story and I suspect relates to transformer winding methods.
>
>
>Mu-metal on its own isn't all that good. It has high magnetic=20
>susceptibility but isn't that good a conductor. It needs a layer of very=
=20
>good conductor on top to generate field cancelling eddy currents.=20
>Bacofoil will do at a pinch.
>
>Regards,
>Martin Brown

Martin, you do not seem to quite get the application domain issues
yet.  The objective is to maintain ultralow EM interference systems in
the presence of high magnitude intermittent incident EM interference,
in RF regions, ultrasonic regions, and audio regions for both
conducted and radiated (including partially rectified and reradiated)
cases.

On Thu, 21 May 2009 21:58:34 +0100, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

>
>
>Vladimir Vassilevsky wrote:
>
>> Eeyore wrote:
>>
>> > What I will need to do however is to filter all the mains =
frequencies
>> > and harmonics to a very large degree.
>> >
>> > I imagine I would need for example to null 50 Hz +/- 2 Hz to ~ =
-100dB. I
>> > have done only a little DSP ( I can't see it happening with analogue
>> > filters ) and I don't even know where to begin with such a severe =
filter
>> > without affecting the pass-band. Same will go for harmonics up to =
some
>> > serious number.
>>
>> The multiple notch filter is simple enough, however it will create the
>> audible artifacts, and it won't do much help against the power =
interference.
>
>It's the interference I want to discriminate from the power line =
fundamental and
>harmonics and see in real time.
>
>
>> > Can  anyone offer some advice as to algorithms ( number of cycles =
for
>> > such a deep notch )
>>
>> Short answer: that won't work.
>
>Not sure what you mean there. I've only a small experience of DSP =
filtering you
>see, although I've done some moderately complex audio reverb processing.
>
>
>> > and even better, a readily available eval board upon
>> > which it could be set up ?
>>
>> Use a PC with a sound card.
>
>Could do, although I'd prefer a 'one box' solution.
>
>
>> > Remember I only need to 'hear' audio band, so
>> > 44.1 or 48 kHz sampling should be OK esp given the oversampling ADCs
>> > today.
>>
>> In the broadcasting equipment, they used to inject the AC frequency =
and
>> its harmonics into the audio to cancel out the power interference.
>
>That must have been ages ago or specific to broadcast. Besides anything =
that
>moves over about 200m gets digitised and goes up fibre optic these days.=
 Not a
>technique ever used in recording studios I've ever seen and that goes =
back a
>bit.
>
>
>> The phases and amplitudes were adjusted for maximum rejection. That =
helped
>> to some extent, however the power interference is rather nonlinear and
>> nonstationary, which makes the problem difficult and non-trivial.
>
>Exactly.
>
>
>> So you shouldn't expect the miraculous improvement anyway.
>
>I think you may have misinterpreted what I'm seeking. Tim Wescott's =
second post
>hit the nail on the head.
>
>Graham

I would have to say close.  Your issue is to find, identify	and deal
with interference sources, both conducted and radiated.

On Thu, 21 May 2009 21:48:23 -0700 (PDT), "miso@sushi.com"
<miso@sushi.com> wrote:

>On May 21, 2:04=A0pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
>wrote:
>> "m...@sushi.com" wrote:
>> > Eeyore <rabbitsfriendsandrelati...@hotmail.com> wrote:
>>
>> > > I am proposing to engage on a project regarding mains voltage =
'purity'
>> > > (and absence of ) with regard to audible clicks and pops in =
high-end
>> > > professional and hi-fi audio equipment.
>>
>> > > Typical EMC filters operate in the RF band and are threfore no use=
 to
>> > > filter audio 'in band' noise that can travel through transformer
>> > > interwinding capacitance etc.
>>
>> > > I have found some of the TI INA series that will with suitable
>> > > preconditioning, tolerate mains voltages and give excellent =
common-mode
>> > > etc rejection. So assembling a 'preamp' front end should be no =
problem.
>>
>> > > What I will need to do however is to filter all the mains =
frequencies
>> > > and harmonics to a very large degree.
>>
>> > > I imagine I would need for example to null 50 Hz +/- 2 Hz to ~ =
-100dB. I
>> > > have done only a little DSP ( I can't see it happening with =
analogue
>> > > filters ) and I don't even know where to begin with such a severe =
filter
>> > > without affecting the pass-band. Same will go for harmonics up to =
some
>> > > serious number.
>>
>> > > Can =A0anyone offer some advice as to algorithms ( number of =
cycles for
>> > > such a deep notch ) and even better, a readily available eval =
board upon
>> > > which it could be set up ? Remember I only need to 'hear' audio =
band, so
>> > > 44.1 or 48 kHz sampling should be OK esp given the oversampling =
ADCs
>> > > today.
>>
>> > I'd be more inclined to sample the AC by phase locking to it.
>>
>> Yes, sampling the mains fundamental would be neat. I don't think you'd=
 even
>> need to be phase locked for simple notch filters.
>>
>> > Then you could easily create a comb filter to kill the power line
>> > fundamental
>> > and harmonics. This implies that you should use a 48kHz sample rate.
>>
>> Readily available.
>>
>> > I'm not sure you need any filtering prior to sampling given the
>> > dynamic range of ADCs these days.
>>
>> Agreed. Just a simple first order at some high frequency for luck =
probably.
>>
>> > If your spike is say 70dB down from the carrier (60/50 Hz mains), I =
can't
>> > believe it be significant to the
>> > power supply design.
>>
>> I wouldn't make ANY assumptions of that nature with today's high SNR =
audio !
>> I've seen some astonishing things.
>>
>> > Besides basic DSP filtering, you could use LMS to get rid of the
>> > fundamental. I suppose you could then LMS for each harmonic.
>>
>> Hadn't thought of LMS. Not looked at it in ages actually. You mean the
>> off-the-shelf package ? A bit pricey IIRC.
>>
>> Graham
>
>I programmed the LMS fit. For the fundamental, you just phase unwrap
>the sampled signal (presumably a sine) with an arcsin. The phase
>versus time plot should be series of points that would ideally be a
>straight line. If you fit a line to these points using LMS, the slope
>will indicate the LMS best fit to frequency. At the time, that was all
>I needed to do. But later I hacked a bit by creating a perfect sine
>wave using this LMS derived slope. I don't recall how I did the
>amplitude fit, but I think I didn't do LMS, but just ran some
>optimizer to vary the amplitude to make the difference between samples
>and the fitted sine wave go to a minimum. This is not a rigorous
>solution to the problem, but probably valid. Note I did this a few
>decades ago, so none of this is perfectly fresh in my mind, but the
>technique as I recall it is sound.
>
>As a hardware person, I think the phase locked sampling and comb
>filter would be the way to go. You probably would have to come up with
>a VXCO for the phase locked source. I hate all this windowing stuff.
>Synchronous sampling is much cleaner.

Sounds nearly sensible to the task, but does not address detecting the
difference of line disturbances very well.

On a sunny day (Mon, 25 May 2009 20:50:48 -0700 (PDT)) it happened
"miso@sushi.com" <miso@sushi.com> wrote in
<d946c8cd-b785-4f80-a7da-97d8bcce5d2f@p6g2000pre.googlegroups.com>:

>It's been my experience that it is easier to compile software under
>Linux. The lack of compilers for windows is the issue.  I assume to
>use the soundcard in windows, you need to use some windows API, and
>the documentation or lack thereof can be frustrating.

humfilter does not use the sound card.
It just creates a filtered wave file from a non-filtered wave file.
there are plenty of free C compilers for MS win,
including MS own one.
But you can cross-compile on Linux too with for example DJ Delories
djgpp as I pointed out.
Or even native in MSDOS.
I do not have it installed, but for 1000 Euro I could [make a DOS
version of humfilter] :-)
Else look here:
 http://www.delorie.com/djgpp/

Anyways, if you port my software (anybody) please keep to the GPL license
conditions.
I do no very actively pursue and search for GPL violations, but the FSF may
torture you and send you to a jail in Cuba :-)

"miso@sushi.com" <miso@sushi.com> wrote:

>On May 25, 2:21=A0pm, pantel...@gmail.com wrote:
>> On May 25, 10:10=A0pm, "m...@sushi.com" <m...@sushi.com> wrote:
>>
>> > You can always dual boot a windows PC.
>>
>> It can be quite a challenge for a non Unix wizzard to start using
>> Linux,
>> especially command line tools like humfilter.
>> As humfitler is a a simple command line program,.
>> written in a simple C, and basically only
>> does wav file format input to wave file output,
>> it should be easily portable to DOS, and run in
>> a MSDOS window in for example XP.
>> Perhaps compile with the old djgpp compiler?
>> Several of my programs have been ported to DOS by people.
>> I am sure you can somehow send the wave output to a soundcard
>> even in MS software.
>
>It's been my experience that it is easier to compile software under
>Linux. The lack of compilers for windows is the issue.  I assume to

Look for Mingw. Thats a GCC that works fine to compile software under
Windows. Still, more complex programs cannot be compiled easely
because of the Linux build tools.

>use the soundcard in windows, you need to use some windows API, and
>the documentation or lack thereof can be frustrating.

Try to find a library that handles that for you.

-- 
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
                     "If it doesn't fit, use a bigger hammer!"
--------------------------------------------------------------

On Tue, 26 May 2009 19:55:38 +0000, Nico Coesel wrote:

>>It's been my experience that it is easier to compile software under
>>Linux. The lack of compilers for windows is the issue.  I assume to
> 
> Look for Mingw. Thats a GCC that works fine to compile software under
> Windows. Still, more complex programs cannot be compiled easely
> because of the Linux build tools.

MSys (hosted on the MinGW site) provides make, a shell, and most of the
common text-processing tools (sed etc). This will allow a lot of Unix
projects to build with little or no modification.

>>use the soundcard in windows, you need to use some windows API, and
>>the documentation or lack thereof can be frustrating.

http://msdn.microsoft.com/en-us/library/ms713503(VS.85).aspx

On Fri, 22 May 2009 20:13:39 +0100, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

>
>
>Nico Coesel wrote:
>
>> Eeyore wrote:
>> >Nils wrote:
>> >
>> >> After reading the discussion I wonder:
>> >>
>> >> Couldn't you simply connect a transformer to the mains, add a =
resistor
>> >> divider at the output to get the signal down and record the =
glitches?
>> >
>> >My front end will do all of that to get the levels right etc. The =
thing is,
>> >you don't seem to be able to see the glitches for the mains, we've =
already
>> >been looking. They must be quite small, or it's getting in via =
another
>>
>> Get a proper digital scope. Many scopes lower their samplerates so you
>> don't see short glitches. Lecroy is bad when it comes to this kind of
>> behaviour. What you need it peak detect.
>
>I agree but it's beyond our budget for this alone. By making dedicated =
kit of
>our own, designed specifically for this kind of job alone we can avoid =
that
>problem.
>
>Graham

Check leasing a good scope for 3 to 6 months.  Might be worth it, then
again it might not.

On May 26, 3:43=A0am, Jan Panteltje <pNaonStpealm...@yahoo.com> wrote:
> On a sunny day (Mon, 25 May 2009 20:50:48 -0700 (PDT)) it happened
> "m...@sushi.com" <m...@sushi.com> wrote in
> <d946c8cd-b785-4f80-a7da-97d8bcce5...@p6g2000pre.googlegroups.com>:
>
> >It's been my experience that it is easier to compile software under
> >Linux. The lack of compilers for windows is the issue. =A0I assume to
> >use the soundcard in windows, you need to use some windows API, and
> >the documentation or lack thereof can be frustrating.
>
> humfilter does not use the sound card.
> It just creates a filtered wave file from a non-filtered wave file.
> there are plenty of free C compilers for MS win,
> including MS own one.
> But you can cross-compile on Linux too with for example DJ Delories
> djgpp as I pointed out.
> Or even native in MSDOS.
> I do not have it installed, but for 1000 Euro I could [make a DOS
> version of humfilter] :-)
> Else look here:
> =A0http://www.delorie.com/djgpp/
>
> Anyways, if you port my software (anybody) please keep to the GPL license
> conditions.
> I do no very actively pursue and search for GPL violations, but the FSF m=
ay
> torture you and send you to a jail in Cuba :-)

A bit off topic, but for those that want to do analysis on a wave
file, you can use sox to convert it into ascii. I've done this to put
sampled signals into spice as a PWL input. Obviously, you need to use
some scripting or write a small program to get the data in spice
format.

Ben Bradley wrote:

>    Here are my thoughts after reading the whole thread (I DID learn C
> 22 years ago - didn't make me rich, but it paid a lot more than
> cleaning toilets in recording studios, and probably even more than
> designing pro audio equipment).
>
> In sci.electronics.design and comp.dsp, On Thu, 21 May 2009 02:54:36
> +0100, Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
>
> >I am proposing to engage on a project regarding mains voltage 'purity'
> >(and absence of ) with regard to audible clicks and pops in high-end
> >professional and hi-fi audio equipment.
> >
> >Typical EMC filters operate in the RF band and are threfore no use to
> >filter audio 'in band' noise that can travel through transformer
> >interwinding capacitance etc.
> >
> >I have found some of the TI INA series that will with suitable
> >preconditioning, tolerate mains voltages and give excellent common-mode
> >etc rejection. So assembling a 'preamp' front end should be no problem.
>
>    From what others posted, I'm thinking you might want to make
> several of these, to also measure things like the neutral voltage and
> the ground voltage (maybe referenced to your own ground stake you put
> in the ground outside the window or door, on the opposite side of the
> building where the main power comes in). Make these to withstand a
> kilovolt or more on the inputs (use several series resistors in each
> leg). That way you can see common-mode signals as well as
> differential.
>
>
> >What I will need to do however is to filter all the mains frequencies
> >and harmonics to a very large degree.
>
>    You say elsewhere you want to see the results in "real time." I
> interpret that as "not having to wait 30 seconds for processing," that
> a half-second or two seconds might be acceptable.
>
>    Others have said it, but I also see this as a PC application. A USB
> audio interface with four inputs should work (you probably want 24bit
> samples - if USB can't do 48/24 and 4 channels, you then use a desktop
> machine (or firewire, whatever), perhaps powered by a battery backup
> to insure line isolation, with a 4=channel or 8-channel card). Three
> inputs are for hot-to-neutral, neutral-to-your-ground,
> ground-to-your-ground, and the forth is the balanced output (with
> ground not connected!) of the mixer/console/UUT.
>
>    You run this thing, and it samples data continuously. When the
> mixer has an output (or when there's an anomalous output on any of the
> other three inputs), the thing samples a few more cycles, then stops
> and does the filtering (on data that's a few cycles long), and shows
> the areas of interest, both with and without the 50/60Hz imposed on
> the hot/neutral input.
>
>    This puts all the algorithms in a PC which has plenty of DSP
> horsepower thesedays, and also makes a good multichannel data
> recorder. I'm thinking you (or someone who knows C and PC code
> development) can get the Audacity source and modify it to do this (I
> don't know of the legalities and such of using the code in a
> commercial product, if you have to make the code you add open-source
> or what).
>
>    And you just might want to have more inputs to look at, such as the
> main DC filtering caps of the console. This would show if the
> transient occurs at a time when the rectifiers are conducting.

Hi Ben,

just wanted to acknowledge the thought you put into this ( along with all
the other useful contributors ). I'm going to chew it over and get back
later.

Graham


--
due to the hugely increased level of spam please make the obvious adjustment
to my email address

On 2009-05-25, panteltje@gmail.com <panteltje@gmail.com> wrote:
> On May 25, 10:10 pm, "m...@sushi.com" <m...@sushi.com> wrote:
>
>> You can always dual boot a windows PC.
>
> It can be quite a challenge for a non Unix wizzard to start using
> Linux,
> especially command line tools like humfilter.
> As humfitler is a a simple command line program,.
> written in a simple C, and basically only
> does wav file format input to wave file output,
> it should be easily portable to DOS, and run in
> a MSDOS window in for example XP.
> Perhaps compile with the old djgpp compiler?

Or compile with the current mingw compiler and run it on the
windows command-line

On 2009-05-26, Nico Coesel <nico@puntnl.niks> wrote:
> "miso@sushi.com" <miso@sushi.com> wrote:
>
>>On May 25, 2:21=A0pm, pantel...@gmail.com wrote:
>>> On May 25, 10:10=A0pm, "m...@sushi.com" <m...@sushi.com> wrote:
>>>
>>> > You can always dual boot a windows PC.
>>>
>>> It can be quite a challenge for a non Unix wizzard to start using
>>> Linux,
>>> especially command line tools like humfilter.
>>> As humfitler is a a simple command line program,.
>>> written in a simple C, and basically only
>>> does wav file format input to wave file output,
>>> it should be easily portable to DOS, and run in
>>> a MSDOS window in for example XP.
>>> Perhaps compile with the old djgpp compiler?
>>> Several of my programs have been ported to DOS by people.
>>> I am sure you can somehow send the wave output to a soundcard
>>> even in MS software.
>>
>>It's been my experience that it is easier to compile software under
>>Linux. The lack of compilers for windows is the issue.  I assume to
>
> Look for Mingw. Thats a GCC that works fine to compile software under
> Windows. Still, more complex programs cannot be compiled easely
> because of the Linux build tools.

You can rin mingw on linux, or many of the build tools are portable
to windows (modulo the limitations of the windows command-line).

Jasen Betts wrote:
> On 2009-05-26, Nico Coesel <nico@puntnl.niks> wrote:
>> "miso@sushi.com" <miso@sushi.com> wrote:
>>
>>> On May 25, 2:21=A0pm, pantel...@gmail.com wrote:
>>>> On May 25, 10:10=A0pm, "m...@sushi.com" <m...@sushi.com> wrote:
>>>>
>>>>> You can always dual boot a windows PC.
>>>> It can be quite a challenge for a non Unix wizzard to start using
>>>> Linux,
>>>> especially command line tools like humfilter.
>>>> As humfitler is a a simple command line program,.
>>>> written in a simple C, and basically only
>>>> does wav file format input to wave file output,
>>>> it should be easily portable to DOS, and run in
>>>> a MSDOS window in for example XP.
>>>> Perhaps compile with the old djgpp compiler?
>>>> Several of my programs have been ported to DOS by people.
>>>> I am sure you can somehow send the wave output to a soundcard
>>>> even in MS software.
>>> It's been my experience that it is easier to compile software under
>>> Linux. The lack of compilers for windows is the issue.  I assume to
>> Look for Mingw. Thats a GCC that works fine to compile software under
>> Windows. Still, more complex programs cannot be compiled easely
>> because of the Linux build tools.
> 
> You can rin mingw on linux, or many of the build tools are portable
> to windows (modulo the limitations of the windows command-line).

Cygwin gives you a proper Linux command line under Windows.

-- 
    W
  . | ,. w ,   "Some people are alive only because
   \|/  \|/     it is illegal to kill them."    Perna condita delenda est
---^----^---------------------------------------------------------------