f



Negative Group Delay ... again!

From a recent discussion here:

> >if i could generate some coefficents that had a 'negative' group delay for
> >a period of time, would you think that 'phase cloning' was new and
> >intersting??
>
> A time machine would be pretty revolutionary, yes.
>
> Negative group delay means that the output appears before the input
> arrives.

Fascinating concept, isn't it? I was curious enough to dig into the
topic for a while and write up what I found out. You can read about it
here:

http://www.dsprelated.com/showarticle/54.php

Regards,
Andor
0
andor.bariska (1307)
3/7/2008 10:18:06 PM
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On Mar 7, 5:18=A0pm, Andor <andor.bari...@gmail.com> wrote:
> From a recent discussion here:
>
> > >if i could generate some coefficents that had a 'negative' group delay =
for
> > >a period of time, would you think that 'phase cloning' was new and
> > >intersting??
>
> > A time machine would be pretty revolutionary, yes.
>
> > Negative group delay means that the output appears before the input
> > arrives.
>
> Fascinating concept, isn't it? I was curious enough to dig into the
> topic for a while and write up what I found out. You can read about it
> here:
>
> http://www.dsprelated.com/showarticle/54.php
>
> Regards,
> Andor

Hello Andor,

Very well written article. Hopefully this will put a lot of the
seeming paradoxes associated with group delay to bed. The previous
threads must have set a limit for their quantity.  Whole books have
been written on this subject as it is quite slippery. The D'enouement
makes itself apparent when you try to trick mother nature and the
predictability goes out the window.  You can have fun by feeding this
circuit's output back to its input and make a negative group delay
oscillator - wouldn't that be odd?

Good Job,

Clay





0
clay (793)
3/7/2008 11:13:43 PM
On Fri, 7 Mar 2008 14:18:06 -0800 (PST), Andor
<andor.bariska@gmail.com> wrote:

>From a recent discussion here:
>
>> >if i could generate some coefficents that had a 'negative' group delay for
>> >a period of time, would you think that 'phase cloning' was new and
>> >intersting??
>>
>> A time machine would be pretty revolutionary, yes.
>>
>> Negative group delay means that the output appears before the input
>> arrives.
>
>Fascinating concept, isn't it? I was curious enough to dig into the
>topic for a while and write up what I found out. You can read about it
>here:
>
>http://www.dsprelated.com/showarticle/54.php
>
>Regards,
>Andor

Nicely done!

Gotta admit, I learned some things there, and the article is good
enough that I do feel I understand the topic better.

Kudos for including the code, too!

But wouldn't it be impressive if I'd said that before the article was
published?

;)



Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.ericjacobsen.org
0
eric.jacobsen (2636)
3/8/2008 2:36:21 AM
On Mar 7, 2:18 pm, Andor <andor.bari...@gmail.com> wrote:
> From a recent discussion here:
>
> > >if i could generate some coefficents that had a 'negative' group delay for
> > >a period of time, would you think that 'phase cloning' was new and
> > >intersting??
>
> > A time machine would be pretty revolutionary, yes.
>
> > Negative group delay means that the output appears before the input
> > arrives.
>
> Fascinating concept, isn't it? I was curious enough to dig into the
> topic for a while and write up what I found out. You can read about it
> here:
>
> http://www.dsprelated.com/showarticle/54.php
>
> Regards,
> Andor

Very nice write-up Andor.

Far from being an impossible time machine, it looks
like any pole(s) inside the unit circle and much nearer
than the canceling zero(s) could have a tiny frequency
band with negative group delay.

So what this says:

> > Negative group delay means that the output appears before the input
> > arrives.

might be be better stated at this:

A filter with negative group delay can produce the output
before the input if the input has been on and continues on
a highly predictable trajectory due to staying completely
within a certain constrained bandwidth.

No violation of causality becaues of the "if" clause.


IMHO. YMMV.
--
rhn A.T nicholson d.0.t C-o-M
0
rhnlogic (1111)
3/8/2008 3:16:19 AM
On Mar 7, 11:18=A0pm, Andor <andor.bari...@gmail.com> wrote:
> From a recent discussion here:
>
> > >if i could generate some coefficents that had a 'negative' group delay =
for
> > >a period of time, would you think that 'phase cloning' was new and
> > >intersting??
>
> > A time machine would be pretty revolutionary, yes.
>
> > Negative group delay means that the output appears before the input
> > arrives.
>
> Fascinating concept, isn't it? I was curious enough to dig into the
> topic for a while and write up what I found out. You can read about it
> here:
>
> http://www.dsprelated.com/showarticle/54.php

Interesting piece. Just a couple of questions:

- Why not use the BLT to transfor to discrete-time domain?
  I don't know Greg's stuff, I am familiar with the properties
  of the BLT.
- Why analyze in discrete-time domain at all? Your results
  would have been seriously interesting if you could demonstrate
  similar effects in continuos-time domain; here they are amusing.
- Why not use the impulse as test signal? You refer to 'some' who
  'claim' that system with negative group delays are noncausal, as
  if you contest (or at least not support) such a view. I have
  made such claims.

Your way of phrasing opens a whole new can of worms of semantic wars
etc - why not demonstarte once and for all that systems with negative
group delays exist and can be implemented in CT? (If that indeed is
your claim, of course; I could not find out from the article what
your stand on the issue is.)

I would suggest the following:

1) Make a clear statement of the 'usual' views on the issue,
   your own opinions, and exactly what this article aims
   to demonstrate.
2) Compute the phase response of the CT system function and
   demonstrate that there is a negative group delay there.
   If you have the tools, I would also suggest you simulate
   the impulse response of that circuit in CT domain.
3) Use standard techniques in DT domain (BLT, Kronecker delta)
   and repeat your analysis.

If all the results persist (system functions show negative
group delays, anticausal behaviour) after such a re-work, I
will consider to spend some time looking into your article
in more detail.

As the article stands, it only cretates confusion. A less
benevolent reviewer than me might sugest that the instability
caused by the truncated signal is caused by poles located
outside the unit circle, and thus suggest that there is a
fundamental flaw in the argument. As you know, if you can
repeat the results using standard analysis tools and from
multiple angles of attack, it will stop those sorts of
argument at the outset.

Rune
0
allnor (8509)
3/8/2008 12:02:43 PM
On Mar 8, 12:02 pm, Rune Allnor <all...@tele.ntnu.no> wrote:
> On Mar 7, 11:18 pm, Andor <andor.bari...@gmail.com> wrote:
>
>
> Interesting piece. Just a couple of questions:
>
> - Why not use the BLT to transfor to discrete-time domain?
>   I don't know Greg's stuff, I am familiar with the properties
>   of the BLT.

I'm not sure it matters what the technique is?  Surely all that
matters is that a discrete-time filter is derived that has the key
properties of its CT counterpart (approximately flat -ve group delay
over a region with approximately flat magnitude response).  The fact
that the overall response is roughly the same is merely an aesthetic
bonus.


> - Why analyze in discrete-time domain at all? Your results
>   would have been seriously interesting if you could demonstrate
>   similar effects in continuos-time domain; here they are amusing.
> - Why not use the impulse as test signal? You refer to 'some' who
>   'claim' that system with negative group delays are noncausal, as
>   if you contest (or at least not support) such a view. I have
>   made such claims.

How would you suggest performing the experiment in CT, short of
actually building the circuit?  Even circuit analysis tools have to
operate in discrete time.


> Your way of phrasing opens a whole new can of worms of semantic wars
> etc - why not demonstarte once and for all that systems with negative
> group delays exist and can be implemented in CT? (If that indeed is
> your claim, of course; I could not find out from the article what
> your stand on the issue is.)

It would appear that he has.  He's presented a circuit whose transfer
function is easily derivable, and which clearly has a negative group
delay over some region (as the graph demonstrates).


> I would suggest the following:
>
> 1) Make a clear statement of the 'usual' views on the issue,
>    your own opinions, and exactly what this article aims
>    to demonstrate.
> 2) Compute the phase response of the CT system function and
>    demonstrate that there is a negative group delay there.
>    If you have the tools, I would also suggest you simulate
>    the impulse response of that circuit in CT domain.

I agree that graphs of the impulse responses would have been nice.
But on the other hand, they're kind of irrelevant to the argument, as
it is clear that both systems are causal!

> 3) Use standard techniques in DT domain (BLT, Kronecker delta)
>    and repeat your analysis.
>
> If all the results persist (system functions show negative
> group delays, anticausal behaviour) after such a re-work, I
> will consider to spend some time looking into your article
> in more detail.

I believe the point of the article was precisely to counter the belief
that -ve group delay equates to "anticausal behaviour".

>
> As the article stands, it only cretates confusion. A less
> benevolent reviewer than me might sugest that the instability
> caused by the truncated signal is caused by poles located
> outside the unit circle, and thus suggest that there is a
> fundamental flaw in the argument. As you know, if you can
> repeat the results using standard analysis tools and from
> multiple angles of attack, it will stop those sorts of
> argument at the outset.

Even if there were poles outside the unit circle, that wouldn't allow
the system to become non-causal!  The article already states that both
CT and DT filters are minimum-phase.  A trivial analysis of the
transfer function polynomials demonstrates that they are stable.


--
Oli

0
catch (918)
3/8/2008 1:38:21 PM
On Mar 8, 2:38=A0pm, Oli Charlesworth <ca...@olifilth.co.uk> wrote:
> On Mar 8, 12:02 pm, Rune Allnor <all...@tele.ntnu.no> wrote:
>
> > On Mar 7, 11:18 pm, Andor <andor.bari...@gmail.com> wrote:
>
> > Interesting piece. Just a couple of questions:
>
> > - Why not use the BLT to transfor to discrete-time domain?
> > =A0 I don't know Greg's stuff, I am familiar with the properties
> > =A0 of the BLT.
>
> I'm not sure it matters what the technique is?

It does to me. A result derived with a known, well-udnerstood
technique has a far greater impact than a unfamiliar, possibly
novel technique applied to a tricky question.

>=A0Surely all that
> matters is that a discrete-time filter is derived that has the key
> properties of its CT counterpart (approximately flat -ve group delay
> over a region with approximately flat magnitude response). =A0The fact
> that the overall response is roughly the same is merely an aesthetic
> bonus.

Wrong. If the claim applies to the CT cirquit, it is the CT
cirquit which must be analyzed.

> > - Why analyze in discrete-time domain at all? Your results
> > =A0 would have been seriously interesting if you could demonstrate
> > =A0 similar effects in continuos-time domain; here they are amusing.
> > - Why not use the impulse as test signal? You refer to 'some' who
> > =A0 'claim' that system with negative group delays are noncausal, as
> > =A0 if you contest (or at least not support) such a view. I have
> > =A0 made such claims.
>
> How would you suggest performing the experiment in CT, short of
> actually building the circuit? =A0Even circuit analysis tools have to
> operate in discrete time.

Derive and analyze the Laplace transform for the cirquit?
All analytical, should be easy.

> > Your way of phrasing opens a whole new can of worms of semantic wars
> > etc - why not demonstarte once and for all that systems with negative
> > group delays exist and can be implemented in CT? (If that indeed is
> > your claim, of course; I could not find out from the article what
> > your stand on the issue is.)
>
> It would appear that he has. =A0He's presented a circuit whose transfer
> function is easily derivable, and which clearly has a negative group
> delay over some region (as the graph demonstrates).

Well, that's *not* what the article says. The statement

"We will now proceed to find a discrete filter with
 comparable characteristics in order to be able to
 reproduce the experiment in Matlab world."

can only be interpreted as if the subsequent analysis
applies to the DT "comparable" system.

> > I would suggest the following:
>
> > 1) Make a clear statement of the 'usual' views on the issue,
> > =A0 =A0your own opinions, and exactly what this article aims
> > =A0 =A0to demonstrate.
> > 2) Compute the phase response of the CT system function and
> > =A0 =A0demonstrate that there is a negative group delay there.
> > =A0 =A0If you have the tools, I would also suggest you simulate
> > =A0 =A0the impulse response of that circuit in CT domain.
>
> I agree that graphs of the impulse responses would have been nice.
> But on the other hand, they're kind of irrelevant to the argument, as
> it is clear that both systems are causal!

That's what confuses me:

- I can't figure out what the claim in the article is; what is
  the 'usual' stand on the question and how is it contested?
- What is the premise for the debate? Are we talking about
  CT or DT systems? Online or offline in case of DT? Causal?
  Stable?
- What are the arguments? I don't know the Berchin method for
  CT->DT transform; if the claims are valid they should work
  just as well with the well-known BLT.
- What are the conclusions? I see some graphs but because
  I'm completely lost in earlier stages I don't understand
  what they signify or what the impact is.

> > 3) Use standard techniques in DT domain (BLT, Kronecker delta)
> > =A0 =A0and repeat your analysis.
>
> > If all the results persist (system functions show negative
> > group delays, anticausal behaviour) after such a re-work, I
> > will consider to spend some time looking into your article
> > in more detail.
>
> I believe the point of the article was precisely to counter the belief
> that -ve group delay equates to "anticausal behaviour".

If so, the article would benefit greatly from a better structure
and presentation.

> > As the article stands, it only cretates confusion. A less
> > benevolent reviewer than me might sugest that the instability
> > caused by the truncated signal is caused by poles located
> > outside the unit circle, and thus suggest that there is a
> > fundamental flaw in the argument. As you know, if you can
> > repeat the results using standard analysis tools and from
> > multiple angles of attack, it will stop those sorts of
> > argument at the outset.
>
> Even if there were poles outside the unit circle, that wouldn't allow
> the system to become non-causal! =A0The article already states that both
> CT and DT filters are minimum-phase. =A0A trivial analysis of the
> transfer function polynomials demonstrates that they are stable.

Again, that may be the case but I am not able to follow
the chain of arguments to reach that conclusion.

Rune
0
allnor (8509)
3/8/2008 2:01:21 PM
On Mar 8, 2:01 pm, Rune Allnor <all...@tele.ntnu.no> wrote:
> On Mar 8, 2:38 pm, Oli Charlesworth <ca...@olifilth.co.uk> wrote:
>
> > I'm not sure it matters what the technique is?
>
> It does to me. A result derived with a known, well-udnerstood
> technique has a far greater impact than a unfamiliar, possibly
> novel technique applied to a tricky question.

Perhaps.

> > Surely all that
> > matters is that a discrete-time filter is derived that has the key
> > properties of its CT counterpart (approximately flat -ve group delay
> > over a region with approximately flat magnitude response).  The fact
> > that the overall response is roughly the same is merely an aesthetic
> > bonus.
>
> Wrong. If the claim applies to the CT cirquit, it is the CT
> cirquit which must be analyzed.

Not necessarily.  See further down...

> > How would you suggest performing the experiment in CT, short of
> > actually building the circuit?  Even circuit analysis tools have to
> > operate in discrete time.
>
> Derive and analyze the Laplace transform for the cirquit?
> All analytical, should be easy.

Yes, we could analyse via the Laplace domain by putting in a signal
with a known equation, and examining the output signal's equation.
But given that the group delay and magnitude responses aren't
completely flat (over the bandlimited region of interest), there will
clearly be some distortion, so it's not going to be a case of y(t) =
x(t + T).  As far as I can see, the next logical step in analysing the
"delay" would be to graph both input and output signals.  But clearly,
the graphing process requires discretising the time axis.


> > It would appear that he has.  He's presented a circuit whose transfer
> > function is easily derivable, and which clearly has a negative group
> > delay over some region (as the graph demonstrates).
>
> Well, that's *not* what the article says. The statement
>
> "We will now proceed to find a discrete filter with
>  comparable characteristics in order to be able to
>  reproduce the experiment in Matlab world."
>
> can only be interpreted as if the subsequent analysis
> applies to the DT "comparable" system.

Figure 2 shows the group delay of the CT system (in blue); i.e. it has
already been demonstrated that the CT system has -ve group delay.


> > I agree that graphs of the impulse responses would have been nice.
> > But on the other hand, they're kind of irrelevant to the argument, as
> > it is clear that both systems are causal!
>
> That's what confuses me:
>
> - I can't figure out what the claim in the article is; what is
>   the 'usual' stand on the question and how is it contested?
> - What is the premise for the debate? Are we talking about
>   CT or DT systems? Online or offline in case of DT? Causal?
>   Stable?
> - What are the arguments? I don't know the Berchin method for
>   CT->DT transform; if the claims are valid they should work
>   just as well with the well-known BLT.
> - What are the conclusions? I see some graphs but because
>   I'm completely lost in earlier stages I don't understand
>   what they signify or what the impact is.

Andor would be able to answer these questions better than I, but here
is my guess.

I think it is clear that the article is discussing causal, stable
systems, given that the two systems presented are both causal and
stable, and that the typical confusion about -ve group delay is that
it somehow violates causality in practical (i.e. stable) systems.
Whether we're talking about online or offline processing is
irrelevant, as this doesn't affect the property of causality (at
least, not as far as analysing an impulse response is concerned).

In my opinion, the abstract states what the article is trying to
address (i.e. its "arguments").  Namely, the surpise/confusion that
many people exhibit when confronted with the topic of -ve group delay.

I believe the purpose of the article was to demonstrate that -ve group
delay is possible; the experiments in the DT domain clearly
demonstrate this, along with the apparently non-intuitive illusion of
non-causality.  The article concludes with an explanation for this
illusion.  Although there is no proof, surely it is logical to
conclude that if the apparent paradox has been cleared up in the DT
domain, it also serves to clear up any apparent paradox in the CT
domain?  Therefore, I'm not sure that it matters what the specific
discretisation technique was.

> > I believe the point of the article was precisely to counter the belief
> > that -ve group delay equates to "anticausal behaviour".
>
> If so, the article would benefit greatly from a better structure
> and presentation.

Perhaps.

> > Even if there were poles outside the unit circle, that wouldn't allow
> > the system to become non-causal!  The article already states that both
> > CT and DT filters are minimum-phase.  A trivial analysis of the
> > transfer function polynomials demonstrates that they are stable.
>
> Again, that may be the case but I am not able to follow
> the chain of arguments to reach that conclusion.

I'm not sure the chain of arguments affects a numerical analysis of
the transfer function polynomials...


--
Oli

0
catch (918)
3/8/2008 2:43:22 PM
On Mar 8, 2:43 pm, Oli Charlesworth <ca...@olifilth.co.uk> wrote:
> On Mar 8, 2:01 pm, Rune Allnor <all...@tele.ntnu.no> wrote:
>
> > > How would you suggest performing the experiment in CT, short of
> > > actually building the circuit?  Even circuit analysis tools have to
> > > operate in discrete time.
>
> > Derive and analyze the Laplace transform for the cirquit?
> > All analytical, should be easy.
>
> Yes, we could analyse via the Laplace domain by putting in a signal
> with a known equation, and examining the output signal's equation.
> But given that the group delay and magnitude responses aren't
> completely flat (over the bandlimited region of interest), there will
> clearly be some distortion, so it's not going to be a case of y(t) =
> x(t + T).  As far as I can see, the next logical step in analysing the
> "delay" would be to graph both input and output signals.  But clearly,
> the graphing process requires discretising the time axis.
>

Just realised that this is irrelevant, and should be ignored!  You are
right, a CT analysis would be tractable.


--
Oli
0
catch (918)
3/8/2008 2:50:36 PM
On Mar 8, 3:43=A0pm, Oli Charlesworth <ca...@olifilth.co.uk> wrote:
> On Mar 8, 2:01 pm, Rune Allnor <all...@tele.ntnu.no> wrote:
>
> > On Mar 8, 2:38 pm, Oli Charlesworth <ca...@olifilth.co.uk> wrote:
>
> > > I'm not sure it matters what the technique is?
>
> > It does to me. A result derived with a known, well-udnerstood
> > technique has a far greater impact than a unfamiliar, possibly
> > novel technique applied to a tricky question.
>
> Perhaps.

Certainly. If a conclusion depends on using a novel method
to do a standard computation, the first awkward questions
will inevitably concern the soundness of this new method.
It will only strengthen the conclusion if it can be demonstrated
that the conclusion is independent of numerical methods used.


> > > Surely all that
> > > matters is that a discrete-time filter is derived that has the key
> > > properties of its CT counterpart (approximately flat -ve group delay
> > > over a region with approximately flat magnitude response). =A0The fact=

> > > that the overall response is roughly the same is merely an aesthetic
> > > bonus.
>
> > Wrong. If the claim applies to the CT cirquit, it is the CT
> > cirquit which must be analyzed.
>
> Not necessarily. =A0See further down...
>
> > > How would you suggest performing the experiment in CT, short of
> > > actually building the circuit? =A0Even circuit analysis tools have to
> > > operate in discrete time.
>
> > Derive and analyze the Laplace transform for the cirquit?
> > All analytical, should be easy.
>
> Yes, we could analyse via the Laplace domain by putting in a signal
> with a known equation, and examining the output signal's equation.

No. The LT describes the linear system regardless of
input and output signals. If the LP is invalid, then
the system is nonlinear and thus the concept of group
delay is undefined.

Thanks for pointing out another item for my list of points
that ought to be clarified.

Rune
0
allnor (8509)
3/8/2008 2:55:38 PM
On Mar 7, 5:18=A0pm, Andor <andor.bari...@gmail.com> wrote:
> From a recent discussion here:
>
> > >if i could generate some coefficents that had a 'negative' group delay =
for
> > >a period of time, would you think that 'phase cloning' was new and
> > >intersting??
>
> > A time machine would be pretty revolutionary, yes.
>
> > Negative group delay means that the output appears before the input
> > arrives.
>
> Fascinating concept, isn't it? I was curious enough to dig into the
> topic for a while and write up what I found out. You can read about it
> here:
>
> http://www.dsprelated.com/showarticle/54.php
>
> Regards,
> Andor

thank you

Fig 6 was facinating...

Could you reproduce Fig 6 except start at T=3D0?

It would be interesting to see what happens at the very
(unpredictable) start of the input signal.

I'm going to build one of these and go to Wall Street  :-).
Too bad stock numbers are not bandlimted  :-(

Mark





0
makolber (619)
3/8/2008 2:57:15 PM
On Mar 8, 2:55 pm, Rune Allnor <all...@tele.ntnu.no> wrote:
> On Mar 8, 3:43 pm, Oli Charlesworth <ca...@olifilth.co.uk> wrote:
>
> > On Mar 8, 2:01 pm, Rune Allnor <all...@tele.ntnu.no> wrote:
>
> > > On Mar 8, 2:38 pm, Oli Charlesworth <ca...@olifilth.co.uk> wrote:
>
> > > > I'm not sure it matters what the technique is?
>
> > > It does to me. A result derived with a known, well-udnerstood
> > > technique has a far greater impact than a unfamiliar, possibly
> > > novel technique applied to a tricky question.
>
> > Perhaps.
>
> Certainly. If a conclusion depends on using a novel method
> to do a standard computation, the first awkward questions
> will inevitably concern the soundness of this new method.
> It will only strengthen the conclusion if it can be demonstrated
> that the conclusion is independent of numerical methods used.
>
>
>
> > > > Surely all that
> > > > matters is that a discrete-time filter is derived that has the key
> > > > properties of its CT counterpart (approximately flat -ve group delay
> > > > over a region with approximately flat magnitude response).  The fact
> > > > that the overall response is roughly the same is merely an aesthetic
> > > > bonus.
>
> > > Wrong. If the claim applies to the CT cirquit, it is the CT
> > > cirquit which must be analyzed.
>
> > Not necessarily.  See further down...
>
> > > > How would you suggest performing the experiment in CT, short of
> > > > actually building the circuit?  Even circuit analysis tools have to
> > > > operate in discrete time.
>
> > > Derive and analyze the Laplace transform for the cirquit?
> > > All analytical, should be easy.
>
> > Yes, we could analyse via the Laplace domain by putting in a signal
> > with a known equation, and examining the output signal's equation.
>
> No. The LT describes the linear system regardless of
> input and output signals. If the LP is invalid, then
> the system is nonlinear and thus the concept of group
> delay is undefined.

Not sure I understand.  It's a given that the continuous-time system
is LTI, therefore we can apply the LT.  In what way would it be
invalid?


--
Oli

0
catch (918)
3/8/2008 3:00:07 PM
On Mar 8, 4:00=A0pm, Oli Charlesworth <ca...@olifilth.co.uk> wrote:
> On Mar 8, 2:55 pm, Rune Allnor <all...@tele.ntnu.no> wrote:
>
>
>
>
>
> > On Mar 8, 3:43 pm, Oli Charlesworth <ca...@olifilth.co.uk> wrote:
>
> > > On Mar 8, 2:01 pm, Rune Allnor <all...@tele.ntnu.no> wrote:
>
> > > > On Mar 8, 2:38 pm, Oli Charlesworth <ca...@olifilth.co.uk> wrote:
>
> > > > > I'm not sure it matters what the technique is?
>
> > > > It does to me. A result derived with a known, well-udnerstood
> > > > technique has a far greater impact than a unfamiliar, possibly
> > > > novel technique applied to a tricky question.
>
> > > Perhaps.
>
> > Certainly. If a conclusion depends on using a novel method
> > to do a standard computation, the first awkward questions
> > will inevitably concern the soundness of this new method.
> > It will only strengthen the conclusion if it can be demonstrated
> > that the conclusion is independent of numerical methods used.
>
> > > > > Surely all that
> > > > > matters is that a discrete-time filter is derived that has the key=

> > > > > properties of its CT counterpart (approximately flat -ve group del=
ay
> > > > > over a region with approximately flat magnitude response). =A0The =
fact
> > > > > that the overall response is roughly the same is merely an aesthet=
ic
> > > > > bonus.
>
> > > > Wrong. If the claim applies to the CT cirquit, it is the CT
> > > > cirquit which must be analyzed.
>
> > > Not necessarily. =A0See further down...
>
> > > > > How would you suggest performing the experiment in CT, short of
> > > > > actually building the circuit? =A0Even circuit analysis tools have=
 to
> > > > > operate in discrete time.
>
> > > > Derive and analyze the Laplace transform for the cirquit?
> > > > All analytical, should be easy.
>
> > > Yes, we could analyse via the Laplace domain by putting in a signal
> > > with a known equation, and examining the output signal's equation.
>
> > No. The LT describes the linear system regardless of
> > input and output signals. If the LP is invalid, then
> > the system is nonlinear and thus the concept of group
> > delay is undefined.
>
> Not sure I understand. =A0It's a given that the continuous-time system
> is LTI, therefore we can apply the LT. =A0In what way would it be
> invalid?

Just ignore the above. I was writing the above at the same time you
wrote your correction to that same section. I was just trying to say
that if the LT does not apply, then the system is nonlinear and this
whole discussion is irrelevant.

We agree that everything is linear (well, I take Andor's word for
it since it is 15 years since I used the LT), we agree that the LT
applies, and we agree that a CT analysis is feasible.

Rune
0
allnor (8509)
3/8/2008 3:11:26 PM
Oli Charlesworth wrote:

   ...

> Not sure I understand.  It's a given that the continuous-time system
> is LTI, therefore we can apply the LT.  In what way would it be
> invalid?

Hey, fellows, this had been rehashed often in the past under a different 
guise. The optical equivalent of this apparent "prediction" is found so 
often in cases of anomalous diepersion, that the phenomenon is known by 
that name when in fact it is only a consequence of it. There's a simple 
explanation at http://tinyurl.com/3dqx49

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
0
jya (12871)
3/8/2008 3:50:45 PM
Mark wrote:

   ...

> I'm going to build one of these and go to Wall Street  :-).

You miss the point. There is no prediction.

> Too bad stock numbers are not bandlimted  :-(

Thank your lucky stars. :-) That will let you keep your shirt.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
0
jya (12871)
3/8/2008 3:53:21 PM
On Sat, 8 Mar 2008 06:57:15 -0800 (PST), Mark <makolber@yahoo.com>
wrote:

>On Mar 7, 5:18�pm, Andor <andor.bari...@gmail.com> wrote:
>> From a recent discussion here:
>>
>> > >if i could generate some coefficents that had a 'negative' group delay for
>> > >a period of time, would you think that 'phase cloning' was new and
>> > >intersting??
>>
>> > A time machine would be pretty revolutionary, yes.
>>
>> > Negative group delay means that the output appears before the input
>> > arrives.
>>
>> Fascinating concept, isn't it? I was curious enough to dig into the
>> topic for a while and write up what I found out. You can read about it
>> here:
>>
>> http://www.dsprelated.com/showarticle/54.php
>>
>> Regards,
>> Andor
>
>thank you
>
>Fig 6 was facinating...
>
>Could you reproduce Fig 6 except start at T=0?
>
>It would be interesting to see what happens at the very
>(unpredictable) start of the input signal.
>
>I'm going to build one of these and go to Wall Street  :-).
>Too bad stock numbers are not bandlimted  :-(
>
>Mark

This guy seems to think they are:

http://www.xyber9.com/Xyber9/Home.aspx

I like the "nominated for the Nobel Prize in Economics" marketing.   I
think the threshold for nomination isn't very tough to cross.   We
should all nominate each other for some big prize, or at least some
prize with a big sounding name.

Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.ericjacobsen.org
0
eric.jacobsen (2636)
3/8/2008 4:54:46 PM
On 8 Mrz., 15:57, Mark <makol...@yahoo.com> wrote:
> On Mar 7, 5:18=A0pm, Andor <andor.bari...@gmail.com> wrote:
>
>
>
>
>
> > From a recent discussion here:
>
> > > >if i could generate some coefficents that had a 'negative' group dela=
y for
> > > >a period of time, would you think that 'phase cloning' was new and
> > > >intersting??
>
> > > A time machine would be pretty revolutionary, yes.
>
> > > Negative group delay means that the output appears before the input
> > > arrives.
>
> > Fascinating concept, isn't it? I was curious enough to dig into the
> > topic for a while and write up what I found out. You can read about it
> > here:
>
> >http://www.dsprelated.com/showarticle/54.php
>
> > Regards,
> > Andor
>
> thank you
>
> Fig 6 was facinating...
>
> Could you reproduce Fig 6 except start at T=3D0?
>
> It would be interesting to see what happens at the very
> (unpredictable) start of the input signal.

The filter oscillates wildly for about one second (the same as with
the truncated pulse) with a max amplitude of 1800.

>
> I'm going to build one of these and go to Wall Street =A0:-).
> Too bad stock numbers are not bandlimted =A0:-(

In that case, I suggest a good old time advance. Works also for non-
bandlimited signals :-).

Regards,
Andor
0
andor.bariska (1307)
3/9/2008 6:18:58 PM
Ron wrote:

> A filter with negative group delay can produce the output
> before the input if the input has been on and continues on
> a highly predictable trajectory due to staying completely
> within a certain constrained bandwidth.
>
> No violation of causality becaues of the "if" clause.

That is a great nutshell explanation. Thanks!

Regards,
Andor
0
andor.bariska (1307)
3/9/2008 6:20:08 PM
On Sat, 08 Mar 2008 09:54:46 -0700, Eric Jacobsen
<eric.jacobsen@ieee.org> wrote:

   (snipped by Lyons)
>
>This guy seems to think they are:
>
>http://www.xyber9.com/Xyber9/Home.aspx
>
>I like the "nominated for the Nobel Prize in Economics" marketing.   I
>think the threshold for nomination isn't very tough to cross.   We
>should all nominate each other for some big prize, or at least some
>prize with a big sounding name.
>
>Eric Jacobsen

Hi Eric,
  actually, the guys frequenting this comp.dsp 
newsgroup have be "nominated" for something.
Each of us was designated as Time Magazine's 
"Person of the Year" for 2006.  That includes 
you Eric, which means you can add that accolade 
to your resume!

[-Rick-]
0
Rick
3/9/2008 11:26:38 PM
Eric Jacobsen wrote:
> On Sat, 8 Mar 2008 06:57:15 -0800 (PST), Mark <makolber@yahoo.com>
> wrote:
> 
>> On Mar 7, 5:18 pm, Andor <andor.bari...@gmail.com> wrote:
>>> From a recent discussion here:
>>>
>>>>> if i could generate some coefficents that had a 'negative' group delay for
>>>>> a period of time, would you think that 'phase cloning' was new and
>>>>> intersting??
>>>> A time machine would be pretty revolutionary, yes.
>>>> Negative group delay means that the output appears before the input
>>>> arrives.
>>> Fascinating concept, isn't it? I was curious enough to dig into the
>>> topic for a while and write up what I found out. You can read about it
>>> here:
>>>
>>> http://www.dsprelated.com/showarticle/54.php
>>>
>>> Regards,
>>> Andor
>> thank you
>>
>> Fig 6 was facinating...
>>
>> Could you reproduce Fig 6 except start at T=0?
>>
>> It would be interesting to see what happens at the very
>> (unpredictable) start of the input signal.
>>
>> I'm going to build one of these and go to Wall Street  :-).
>> Too bad stock numbers are not bandlimted  :-(
>>
>> Mark
> 
> This guy seems to think they are:
> 
> http://www.xyber9.com/Xyber9/Home.aspx
> 
> I like the "nominated for the Nobel Prize in Economics" marketing.   I
> think the threshold for nomination isn't very tough to cross.   We
> should all nominate each other for some big prize, or at least some
> prize with a big sounding name.

Even economists accept that if you laid them all end to end they 
couldn't reach a conclusion. What kind of bar could possibly be low 
enough for a nomination threshold?

Steve
0
steveu (1008)
3/10/2008 12:04:53 AM
On Mon, 10 Mar 2008 08:04:53 +0800, Steve Underwood <steveu@dis.org>
wrote:

  (snipped by Lyons)
>
>Even economists accept that if you laid them all end to end they 
>couldn't reach a conclusion. What kind of bar could possibly be low 
>enough for a nomination threshold?
>
>Steve

Hi Steve,
  concerning economists, somewhere I read 
something like: "God made economists in order 
to make astrologers look smart".

[-Rick-]
0
Rick
3/10/2008 1:10:42 AM
"Rick Lyons" <R.Lyons@_BOGUS_ieee.org> wrote in message 
news:dd29t353cgde2en5moemo9qct6bts116ur@4ax.com...
> On Mon, 10 Mar 2008 08:04:53 +0800, Steve Underwood 
> <steveu@dis.org>
> wrote:
>
>  (snipped by Lyons)
>>
>>Even economists accept that if you laid them all end to end 
>>they
>>couldn't reach a conclusion. What kind of bar could possibly 
>>be low
>>enough for a nomination threshold?
>>
>>Steve
>
> Hi Steve,
>  concerning economists, somewhere I read
> something like: "God made economists in order
> to make astrologers look smart".
>

There once was a billboard next to I-85 near the 
Greenville-Spartanburg Airport that said, "If all the 
economists in the world were laid end-to-end, it would be a 
good thing."


0
jh113355 (410)
3/10/2008 1:53:10 AM
On Mon, 10 Mar 2008 08:04:53 +0800, Steve Underwood <steveu@dis.org>
wrote:

>Eric Jacobsen wrote:
>> On Sat, 8 Mar 2008 06:57:15 -0800 (PST), Mark <makolber@yahoo.com>
>> wrote:
>> 
>>> On Mar 7, 5:18 pm, Andor <andor.bari...@gmail.com> wrote:
>>>> From a recent discussion here:
>>>>
>>>>>> if i could generate some coefficents that had a 'negative' group delay for
>>>>>> a period of time, would you think that 'phase cloning' was new and
>>>>>> intersting??
>>>>> A time machine would be pretty revolutionary, yes.
>>>>> Negative group delay means that the output appears before the input
>>>>> arrives.
>>>> Fascinating concept, isn't it? I was curious enough to dig into the
>>>> topic for a while and write up what I found out. You can read about it
>>>> here:
>>>>
>>>> http://www.dsprelated.com/showarticle/54.php
>>>>
>>>> Regards,
>>>> Andor
>>> thank you
>>>
>>> Fig 6 was facinating...
>>>
>>> Could you reproduce Fig 6 except start at T=0?
>>>
>>> It would be interesting to see what happens at the very
>>> (unpredictable) start of the input signal.
>>>
>>> I'm going to build one of these and go to Wall Street  :-).
>>> Too bad stock numbers are not bandlimted  :-(
>>>
>>> Mark
>> 
>> This guy seems to think they are:
>> 
>> http://www.xyber9.com/Xyber9/Home.aspx
>> 
>> I like the "nominated for the Nobel Prize in Economics" marketing.   I
>> think the threshold for nomination isn't very tough to cross.   We
>> should all nominate each other for some big prize, or at least some
>> prize with a big sounding name.
>
>Even economists accept that if you laid them all end to end they 
>couldn't reach a conclusion. What kind of bar could possibly be low 
>enough for a nomination threshold?
>
>Steve

I don't know how low that bar would need to be, but if it has an
elevator and good beer on tap, I'd still find it acceptable. 


;)

Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.ericjacobsen.org
0
eric.jacobsen (2636)
3/10/2008 2:58:57 AM
On Mar 9, 7:20=A0pm, Andor <andor.bari...@gmail.com> wrote:
> Ron wrote:
> > A filter with negative group delay can produce the output
> > before the input if the input has been on and continues on
> > a highly predictable trajectory due to staying completely
> > within a certain constrained bandwidth.
>
> > No violation of causality becaues of the "if" clause.
>
> That is a great nutshell explanation. Thanks!

Well, in the abstract of the article you state that

    "This article aims at pouring oil in the fire and
     causing yet more confusion :-)."

and from that perspective, the above summary might be OK.

A far more intersting question is whether a negative group
delay is non-causal. In that case, the above is not quite
as helpful, simply because it has no practical relevance,
it is only philosophical speculation.

I have explained why in an earlier post:

http://groups.google.com/group/comp.dsp/msg/a10e64239d48d374

Rune
0
allnor (8509)
3/10/2008 7:22:14 AM
On Mar 8, 11:18 am, Andor <andor.bari...@gmail.com> wrote:
> From a recent discussion here:
>
> > >if i could generate some coefficents that had a 'negative' group delay for
> > >a period of time, would you think that 'phase cloning' was new and
> > >intersting??
>
> > A time machine would be pretty revolutionary, yes.
>
> > Negative group delay means that the output appears before the input
> > arrives.
>
> Fascinating concept, isn't it? I was curious enough to dig into the
> topic for a while and write up what I found out. You can read about it
> here:
>
> http://www.dsprelated.com/showarticle/54.php
>
> Regards,
> Andor

There is another way to do this. Take an integrator say K/s and put a
pure time-delay in it's feedback path exp(-sT).

Hence G(s) =K/s and H(s)=exp(-sT). At low frequencies we can easily
show that the closed-loop system G/(1+GH) is approx 1/exp(-sT) or
exp(sT)!!
Now in actual fact before people start jumping up and down you can
make this closed -loop system stable - but not stable enough to
predict the future. For a given bandwidth the overshoot you get
appears to be always greater than the delay (or advance) T.You can
introduce phase-lead to further stabilise but I didn't see any vortex
opening..

Hardy
0
gyansorova (941)
3/10/2008 7:47:30 AM
Rune Allnor wrote:

> A far more intersting question is whether a negative group
> delay is non-causal.

You seem to have comletely missed the whole point of the exercise.
Sorry about the confusion part :-).

Regards,
Andor
0
andor.bariska (1307)
3/10/2008 8:40:41 AM
On Mar 10, 9:40=A0am, Andor <andor.bari...@gmail.com> wrote:
> Rune Allnor wrote:
> > A far more intersting question is whether a negative group
> > delay is non-causal.
>
> You seem to have comletely missed the whole point of the exercise.

At first, certainly. But I think I sorted it out eventually.

> Sorry about the confusion part :-).

Well, thanks for initiating that excercise.

Rune
0
allnor (8509)
3/10/2008 10:05:54 AM
On 10 Mrz., 11:05, Rune Allnor <all...@tele.ntnu.no> wrote:
> On Mar 10, 9:40=A0am, Andor <andor.bari...@gmail.com> wrote:
>
> > Rune Allnor wrote:
> > > A far more intersting question is whether a negative group
> > > delay is non-causal.
>
> > You seem to have comletely missed the whole point of the exercise.
>
> At first, certainly. But I think I sorted it out eventually.

My reply was a bit short, sorry about that. Well, the idea was to
start with a circuit which was definitely and unrefutably causal and
show how negative group delay leads to prediction in that case. So non-
causality was ruled out from the start.

> > Sorry about the confusion part :-).
>
> Well, thanks for initiating that excercise.

I sure enjoyed the exercise :-).

Regards,
Andor
0
andor.bariska (1307)
3/10/2008 10:31:40 AM
>On 10 Mrz., 11:05, Rune Allnor <all...@tele.ntnu.no> wrote:
>> On Mar 10, 9:40=A0am, Andor <andor.bari...@gmail.com> wrote:
>>
>> > Rune Allnor wrote:
>> > > A far more intersting question is whether a negative group
>> > > delay is non-causal.
>>
>> > You seem to have comletely missed the whole point of the exercise.
>>
>> At first, certainly. But I think I sorted it out eventually.
>
>My reply was a bit short, sorry about that. Well, the idea was to
>start with a circuit which was definitely and unrefutably causal and
>show how negative group delay leads to prediction in that case. So non-
>causality was ruled out from the start.
>
>> > Sorry about the confusion part :-).
>>
>> Well, thanks for initiating that excercise.
>
>I sure enjoyed the exercise :-).
>
>Regards,
>Andor


Dr Andor.
 
Your explanation is indeed 'phase cloning'. Rune asked me to disclose th
'trick'.  And thats what phase cloning is all about. Its a seeming way t
predict the future.  If one knows what two signals go into the black box
we can predict the future exactly and compensate for it.  You talked o
oversampling., I erroneously called it 'resolution', however, it is indee
oversampling.  Thats why im having problems getting the number of tap
down.

That being said, i believe, if we stomach the oversampling issue, we ca
create filters that have an exact magnitude and phase response w
specify.

Negative group delay cant be real. Im just using a digital computer t
create a situation where the math works out, and thats enough to satisf
causality.
0
cweston_ (73)
3/10/2008 12:43:28 PM
westocl wrote:

   ...

> Negative group delay cant be real. Im just using a digital computer to
> create a situation where the math works out, and thats enough to satisfy
> causality.

Real negative group delay can occur. Its inevitable association with 
appropriate phase delay is the constraint on it that keeps it causal.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
0
jya (12871)
3/10/2008 5:24:57 PM
>westocl wrote:
>
>   ...
>
>> Negative group delay cant be real. Im just using a digital computer to
>> create a situation where the math works out, and thats enough t
satisfy
>> causality.
>
>Real negative group delay can occur. Its inevitable association with 
>appropriate phase delay is the constraint on it that keeps it causal.
>
>Jerry
>-- 
>Engineering is the art of making what you want from things you can get.
>???????????????????????????????????????????????????????????????????????

Hmph. If we know the time it takes for a digital computer to do it
multiplications, it it fesable to ever say that it is real when we kno
the response comes from mathematics?
0
cweston_ (73)
3/10/2008 5:43:44 PM
westocl wrote:
>> westocl wrote:
>>
>>   ...
>>
>>> Negative group delay cant be real. Im just using a digital computer to
>>> create a situation where the math works out, and thats enough to
> satisfy
>>> causality.
>> Real negative group delay can occur. Its inevitable association with 
>> appropriate phase delay is the constraint on it that keeps it causal.
>>
>> Jerry
>> -- 
>> Engineering is the art of making what you want from things you can get.
>> ???????????????????????????????????????????????????????????????????????
> 
> Hmph. If we know the time it takes for a digital computer to do its
> multiplications, it it fesable to ever say that it is real when we know
> the response comes from mathematics?

To say that what is real, the multiplication? The time? Please clarify.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
0
jya (12871)
3/10/2008 8:27:31 PM
Reply:

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Hi All, I am trying to ignore all the lines C++ which start with comment i.e. // but the comment may be start with <space><space>... // So i am trying to write some regex which is going to be negate of (\s*\/\/) which will match all the line not starting with comment Any idea how to go about it. Thanks for help in advance Vinod vinod wrote: > Hi All, > I am trying to ignore all the lines C++ which start with comment i.e. > // > but the comment may be start with <space><space>... // > > So i am trying to write some regex which is going to be negate ...

group delay equalizer
Hi, Matlab has a function called iirgrpdelay which helps in designing iir group delay equalizer filters. Any idea as to how this function can be re-written for people who are not using matlab? Bharat Pathak "bharat pathak" <bharat@arithos.com> wrote in message news:fs-dnX5z64XJUBTanZ2dnUVZ_hCdnZ2d@giganews.com... > Hi, > > Matlab has a function called iirgrpdelay which helps > in designing iir group delay equalizer filters. This is a shamanistic optimization which tries to match the group delay profile by the brute force tweaking of an allpass function. > Any idea as to how this function can be re-written > for people who are not using matlab? I am glad to see that there are still some real people who dare to live without MatLab. Vladimir Vassilevsky DSP and Mixed Signal Consultant www.abvolt.com On Jan 13, 3:35 am, "bharat pathak" <bha...@arithos.com> wrote: > > Matlab has a function called iirgrpdelay which helps > in designing iir group delay equalizer filters. > > Any idea as to how this function can be re-written > for people who are not using matlab? > i can only suggest to start with the MATLAB source code (i might have an old copy) for iirgrpdelay() and all functions that it depends on, and translate to C or whatever language you like. remember the stupid MATLAB indexing origin property. you might be adjusting some indices by 1. you know, probably everyone he...

CIC Group Delay
I would like to know if I can predict what the group delay of a CIC filter is. I have an agressive FIR BPF where the sample rate is 2000 x the filter bandwidth. The group delay is longer than I would like it to be. Could a CIC filter offer a lower group delay? I'll need to interpolate back to the original sample rate, so I need to take that into consideration as part of the answer. Thanks, in advance. Jim jim_nospam_beasley@yahoo.com wrote: > I would like to know if I can predict what the group delay of a CIC > filter is. What is a CIC filter? Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein "Bob Cain" <arcane@arcanemethods.com> wrote in message news:dii59h19o4@enews4.newsguy.com... > > jim_nospam_beasley@yahoo.com wrote: >> I would like to know if I can predict what the group delay of a CIC >> filter is. http://www.google.com/search?hl=en&q=%22cic+filter%22+%22group+delay%22 > > What is a CIC filter? > http://www.google.com/search?hl=en&q=cic+filter > > Bob > -- > > "Things should be described as simply as possible, but no simpler." > > A. Einstein Simple enough, Bob? ;-) Cheers, Syms. <jim_nospam_beasley@yahoo.com> wrote in message news:1129092761.120373.45800@z14g2000cwz.googlegroups.com... >I would like to know if...

Google groups delay
Anyone noticed that google groups is not updating SAS-L ? Today the newest item is dated 2 days ago. R That's true, very unexpected delays both for new posts and also for replies. Hope will be fixed soon. On Oct 29, 12:33=A0am, Akshaya <akshaya.nathil...@gmail.com> wrote: > That's true, very unexpected delays both for new posts and also for > replies. Hope will be fixed soon. Seems to be back to normal now. R ...

phase to group delay
I designed an algorithm to compute signal delay through an RF channel. I first verified the algorithm using a known IIR model. I managed to get groupdelay of this IIR spot on compared to that given by Matlab function grpdelay(num,den). The algorithm is based on sending frequency sweep chirp signal followed by fft then conversion of phase to groupdelay using the derivative of negative angular phase with respect to angular frequency. The algorithm has been released and is working well. I am now asked if I could apply it to the case when the available test signal is only single tone instead of frequency sweep. I tested my same algorithm on single tone. All looks ok but with a mystery factor of 2 needed to get IIR model groupdelay match that of matlab. I mean if I multiply the computed groupdelay based on fft by 2 then it gets correct with a small margin of error. Any idea what this factor of 2 might be. In both cases I use real only chirp signal or real only single tone and the fft is complex. Processing is identical throughout the algorithm for both cases in every step. Regards Kadhiem kaz <37480@dsprelated> wrote: > I designed an algorithm to compute signal delay through an RF channel. > I first verified the algorithm using a known IIR model. I managed to get > groupdelay of this IIR spot on compared to that given by Matlab function > grpdelay(num,den). The algorithm is based on sending frequency...

Group delay in Matlab
Dear all I not very familiar with filter design in Matlab and I am probably missin something when it comes to "group delay". My problem comes as follows. From what I have understood, if I have a filter such that its group dela response (plotted with grpdelay[b,a] in matlab with a,b the filte coefficients) provides 17 as the group delay (in samples) at f=0.1 (normalized frequency so f=0.14*fs/2=0.14*500=70Hz, sampling frequenc being 1000 Hz) then passing a sinusoid whose frequency is 70Hz through th filter I should get at the output the same sinusoid (assuming gain is one delayed by...

group delay time?
It is known, that non-uniformity of the frequency response of the channel influences level of ISI. And what kind of distortions is characteristic for non-uniform group delay time? On Feb 5, 3:08=A0am, "alex65111" <alex65...@list.ru> wrote: > It is known, that non-uniformity of the frequency response of the channel > influences level of ISI. And what kind of distortions is characteristic f= or > non-uniform group delay time? A non-constant group delay vs frequency (non-linear phase vs frequency) distorts the pulse shape. This causes ISI. John >On Feb 5, 3:08=A0am, "alex65111" <alex65...@list.ru> wrote: >> It is known, that non-uniformity of the frequency response of the channel >> influences level of ISI. And what kind of distortions is characteristic f= >or >> non-uniform group delay time? > >A non-constant group delay vs frequency (non-linear phase vs >frequency) distorts the pulse shape. This causes ISI. > >John > As on level of pulsations group delay it is possible to estimate effective duration of the impulse response? On Feb 5, 3:47=A0pm, "alex65111" <alex65...@list.ru> wrote: > >On Feb 5, 3:08=3DA0am, "alex65111" <alex65...@list.ru> wrote: > >> It is known, that non-uniformity of the frequency response of the > channel > >> influences level of ISI. And what kind of distortions is characteristi= c > f=3D > >or >...

Filter Group Delay
The Matlab command 'grpdelay' is restricted to digital filters only. Does there exist some counterpart to 'grpdelay' that operates in the analog domain? Some Matlab commands have separate versions for the analog and digital domains, and I wonder why 'grpdelay' does not. For example, the 'butter' command to generate Butterworth filter coefficients has digital and analog versions. The analog version is useful for understanding the stand-alone characteristics of a proposed filter, i.e., the characteristics that are independent of a particular sampled data record. ...

delays: inertial delays vs. transport delays
Hello, I have some issues with delays which I would appreciate very much if someone could please clarify for me, as they are not clear to me right now. I would like to know what the difference between an inertial delay and a transport delay is and why VHDL would need to have these two distinct types of delay. Also, it seems to me that specifying delays in VHDL designs can only serve the purose of simulation since the delays inherent in the physical hardware cannot, as far as I know, be controlled with software: they certainly cannot be made smaller than what they are, but I'm not sur...

Linux Fails in Munich, Delays, Delays, Delays
The pipedream of Linux being used by Government is quickly fading. The first big deployment has been full of "snags" and "delays"... just like using Linux! We told everyone this, now the truth is known. - Munich announces delay in Linux migration into 2006 9/7/2005 4:55:02 PM, by Jeremy Reimer The municipal government of Munich, Germany released a statement yesterday that the migration of its office PCs to Linux and OpenOffice.org, which was scheduled to be completed in 2005, has slipped to at least next year. The original plan, which involved switching all 14,00...

RegEx question
Hi all, I have a problem with regular expressions: I need a regular expression that negates a group. An example: I want that all strings starting with "foo" and "bar" don't match. So "fooblabla" should not match, but "foblabla" should. My first, but unfortunately wrong idea: ^[^(foo|bar)].*$ Because [] treats these strings as single characters, so it means NOT (, NOT f, NOT o, ... But how this is possible to do? Is it possible with regular expressions at all? thx, Gerald In article <iZigb.82793$qU6.1336679@news.chello.at>, Gerald Maschl...

Group By, Limit only group?
Greetings. I'm looking to select data from a table and group by some values.. but I'm looking to limit the number of rows returned for each group, but not the entire query. Here's my table set up (Not from MySQL, just typed up.. but it'll give you the idea): CREATE TABLE bank_ident_all_t( ident_id INT(9) UNSIGNED ZEROFILL NOT NULL, ident_type ENUM('ach','cc') NOT NULL, bank_id INT UNSIGNED NOT NULL, ref_count INT UNSIGNED NOT NULL DEFAULT 1, last_updated INT UNSIGNED NOT NULL, PRIMARY KEY(ident_id, ident_type, bank_id), INDEX(ident_id, ident_type) )...

group delay for type3 and type4
Hi, In the book "DSP a practical approach" 2nd Ed by Ifeachor, Jervis it is mentioned that group delay for type 3 and type 4 LPFIR filter is given by Tp = T*(N-1-pi)/2; eq 7.4b page 348 Is it correct to have pi inside the brackets for group delay calculation? Regards Bharat On Mar 25, 2:23=A0am, "bharat pathak" <bha...@arithos.com> wrote: > Hi, > > =A0 In the book "DSP a practical approach" 2nd Ed by Ifeachor, Jervis > =A0 it is mentioned that group delay for type 3 and type 4 LPFIR filter > =A0 is given by > > =A0 Tp =3D T*(N-1-pi)/2; eq 7.4b page 348 > > =A0 Is it correct to have pi inside the brackets for group delay > =A0 calculation? > > Regards > Bharat Hello Bharat, All FIR filters whose impulse responses have definite parity have a group delay of (N-1)/2 samples. By definite parity I mean the coefs are either symmetric or antisymmetric. And N is the length of the impulse response, i.e.,the number of filter taps. Clay >All FIR filters whose impulse responses have definite parity have a >group delay of (N-1)/2 samples. By definite parity I mean the coefs >are either symmetric or antisymmetric. >And N is the length of the impulse response, i.e.,the number of filter >taps. I understand that, my question is should pi appear in the equation for Type3 and Type4 LPFIR filters??? I understand the equation for Type1 and Type2. Regards Bharat On 25 Mrz., 07:...

Is this group only a Google group?
Hello, I'm discovering APL and I posted a question yesterday on the comp.lang.apl = nntp group. While searching for more information about APL, I stumbled upon= this Google group. I see that it has the same posts than the nntp group, b= ut the last nntp post is from October 1st, 2014. I'm thus wondering if there is are synchronization issues between nntp and = the Google group, or if the problem is with my nntp provider. Thanks, Alan Hi, comp.lang.apl is definitely a usenet group. Many providers aren't retaining many newsgroups long enough and also seem to ...

[News] Windows Vista: Delays, Delays, More Delays and Doubt
Microsoft's Vista faces delays as public tests continue ,----[ Quote ] | David Bradshaw, principal analyst for Ovum, the technology research | group, said that delays to the full release of Vista remained a danger, | noting that such testing programmes are becoming increasingly normal. He | said that public testing programmes were useful in highlighting problems | of compatibility, where the software fails to work properly with certain | printers, software programs or hardware. | | Although the discovery of a problem could force a rewrite, Mr Bradshaw | said, "it would have to be a...

Channel-Group Groups
When configuring a T1 and setting up the timeslots you have an option to set the channel group group number. What exactly does the "channel-group" group number do? Normally, I plug in 1, but you can set it from 0-23. channel-group ?? timeslots 1-24 speed 64 (?? is where the group number would go.) Thanks Amy. On 16 Dec 2004 10:53:42 -0800, amyl@paxemail.com wrote: ~ When configuring a T1 and setting up the timeslots you have an option ~ to set the channel group group number. What exactly does the ~ "channel-group" group number do? Normally, I plug in 1, but you can ~ set it from 0-23. ~ ~ channel-group ?? timeslots 1-24 speed 64 ~ (?? is where the group number would go.) ~ ~ Thanks ~ Amy. The channel-group number becomes part of the name of the serial interface you create. For example, if you do this: controller T1 2 channel-group 3 timeslots 1-24 speed 64 then this creates an interface called "Serial 2:3" You can configure multiple channel-groups (and/or ds0-groups if your platform supports it), so pick a unique channel-group/ ds0-group ID for each such group ... e.g. controller t1 2 channel-group 0 timeslots 1-4 speed 64 channel-group 1 timestots 5-12 speed 64 ds0-group 2 timeslots 13-24 type e&m-fgb Aaron ...

Re: Google groups delay
Indeed ... maybe 97000 is a magic number for them (96999 is the number of topics currently listed)? -Joe On Mon, Oct 27, 2008 at 6:41 PM, Richard <richard.hockey@gmail.com> wrote: > Anyone noticed that google groups is not updating SAS-L ? > Today the newest item is dated 2 days ago. > R > ...

Finding the group delay of a filter
Has anyone implemented a function to find the group delay (the time between= the filter's initial response and its peak response)of the different digit= al filters in LabVIEW?<br><br>I need to track the arrival of a certain part= of a signal. I know approx. when it is to arrive, however locating it gets= complicated due to the variable delay caused by the necessary filtering (d= elay depends on the frequencies, filter order, type etc.) .<br><br>I see th= at MatLAB / MatWorks has a group delay function, but perhaps someone has ma= de a G equivalent? <br><br>The digital filter design toolkit is said to hav= e analysis tools that can give you the group delay...but I'm not sure if th= at could be used to find the delay in any case programmatically? Even if it= can I'm a bit reluctant to buy the toolkit just for that functionality...<= br><br>I though I had solved it when I found a description of how to calcul= ate the delay of a Butterworth filter (at least) on: http://www.mathcad.com= /Library/LibraryContent/MathML/group_b.htm<br><br>The results are in the ri= ght ballpark...but sometimes it fails by more than 5 microseconds and that'= s not good enough for my application (could be an incorrect implementation = off course). <br><br>If I use correlation to find the delay I get extremely= good results, however that will not be robust enough (there could be other= strong features, e.g. due...

Filter Design, group delay
Hello, I am looking for a way to obtain the lowest group delay. The specifications are; Lowpass filter fpass=1kHz with 3dB Ripple fstop=4kHz Attenuation 60dB (between 4kHz and 20kHz or between 4kHz and 97.5kHz) with sampling frequency: 195kHz up to 1kHz linear phase and constant group delay (needed) If I use Generalized Equiripple FIR filter of Matlab fda toolbox, th minimum order is 115 (so 57.5 Tabs delay) Is it possible to obtain a new filter which has a delay less than 57. Tabs for the given specifications? Best Regards Gokhan On 12 Okt, 04:58, "gapaydin" <apadi...@yahoo.com> wrote: > Hello, > > I am looking for a way to obtain the lowest group delay. > The specifications are; > > Lowpass filter > fpass=1kHz with 3dB Ripple > fstop=4kHz > Attenuation 60dB (between 4kHz and 20kHz or between 4kHz and 97.5kHz) > with sampling frequency: 195kHz > up to 1kHz linear phase and constant group delay (needed) > > If I use Generalized Equiripple FIR filter of Matlab fda toolbox, the > minimum order is 115 (so 57.5 Tabs delay) > > Is it possible to obtain a new filter which has a delay less than 57.5 > Tabs for the given specifications? I would be very surprised if you can reduce the group delay significantly. Since you require constant group delay you are commited to symmetric FIR filters. Which means that the task is to design the shortest symmetric FIR filter which attains the spec. You may be able to s...

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