f



negative group delay

Hi,

   I am seeing some negative group delay at 
   1000, 2000, 3000, 4000, 5000 Hz. The example
   filter listed below with matlab/octave code.

   any clue why this is happening? interesting
   part is when I feed 1000 hz sine wave sampled
   at 10000 hz I don't see the behaviour of 
   negative group delay.

Regards
Bharat


%----------------------------------------------------------------


clear;
close all;

h1      = [10 9 8 7 6 5 4 3 2 1]/55;
Fs      = 10000;

[gd, f] = grpdelay(h1, 1, 8192, Fs);
figure; clf;
plot(f, gd);

0
bharat310 (236)
3/12/2008 5:58:29 PM
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On Mar 12, 5:58 pm, "bharat pathak" <bha...@arithos.com> wrote:
> Hi,
>
>    I am seeing some negative group delay at
>    1000, 2000, 3000, 4000, 5000 Hz. The example
>    filter listed below with matlab/octave code.
>
>    any clue why this is happening? interesting
>    part is when I feed 1000 hz sine wave sampled
>    at 10000 hz I don't see the behaviour of
>    negative group delay.

Individual sine waves don't experience group delay, they experience
phase delay.


--
Oli

0
catch (918)
3/12/2008 7:04:53 PM
On Mar 12, 11:04 am, Oli Charlesworth <ca...@olifilth.co.uk> wrote:
> On Mar 12, 5:58 pm, "bharat pathak" <bha...@arithos.com> wrote:
>
> > Hi,
>
> >    I am seeing some negative group delay at
> >    1000, 2000, 3000, 4000, 5000 Hz. The example
> >    filter listed below with matlab/octave code.
>
> >    any clue why this is happening? interesting
> >    part is when I feed 1000 hz sine wave sampled
> >    at 10000 hz I don't see the behaviour of
> >    negative group delay.
>
> Individual sine waves don't experience group delay, they experience
> phase delay.

Yes.  To see the group delay you will have to modulate your
sine wave while staying completely within a bandwidth where
the group delay is fairly constant, and then compare the
before and after filtering locations of your modulation
envelope.




0
rhnlogic (1111)
3/12/2008 9:48:16 PM
Ron N. wrote:
> On Mar 12, 11:04 am, Oli Charlesworth <ca...@olifilth.co.uk> wrote:
>> On Mar 12, 5:58 pm, "bharat pathak" <bha...@arithos.com> wrote:
>>
>>> Hi,
>>>    I am seeing some negative group delay at
>>>    1000, 2000, 3000, 4000, 5000 Hz. The example
>>>    filter listed below with matlab/octave code.
>>>    any clue why this is happening? interesting
>>>    part is when I feed 1000 hz sine wave sampled
>>>    at 10000 hz I don't see the behaviour of
>>>    negative group delay.
>> Individual sine waves don't experience group delay, they experience
>> phase delay.
> 
> Yes.  To see the group delay you will have to modulate your
> sine wave while staying completely within a bandwidth where
> the group delay is fairly constant, and then compare the
> before and after filtering locations of your modulation
> envelope.

No modulation needed. three signals close in frequency and amplitude 
will produce beats that _look_ like modulation and illustrate the effect.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
0
jya (12871)
3/13/2008 12:42:48 AM
On Mar 12, 4:42 pm, Jerry Avins <j...@ieee.org> wrote:
> Ron N. wrote:
> > On Mar 12, 11:04 am, Oli Charlesworth <ca...@olifilth.co.uk> wrote:
> >> On Mar 12, 5:58 pm, "bharat pathak" <bha...@arithos.com> wrote:
>
> >>> Hi,
> >>>    I am seeing some negative group delay at
> >>>    1000, 2000, 3000, 4000, 5000 Hz. The example
> >>>    filter listed below with matlab/octave code.
> >>>    any clue why this is happening? interesting
> >>>    part is when I feed 1000 hz sine wave sampled
> >>>    at 10000 hz I don't see the behaviour of
> >>>    negative group delay.
> >> Individual sine waves don't experience group delay, they experience
> >> phase delay.
>
> > Yes.  To see the group delay you will have to modulate your
> > sine wave while staying completely within a bandwidth where
> > the group delay is fairly constant, and then compare the
> > before and after filtering locations of your modulation
> > envelope.
>
> No modulation needed. three signals close in frequency and amplitude
> will produce beats that _look_ like modulation and illustrate the effect.

Well, I sort of agree.  But call any two of those sinusoids
the sidebands produced by complex modulation of the third,
and I think the sum is identical to a form of modulation
with carrier.
0
rhnlogic (1111)
3/13/2008 1:46:59 AM
Ron N. wrote:
> On Mar 12, 4:42 pm, Jerry Avins <j...@ieee.org> wrote:
>> Ron N. wrote:
>>> On Mar 12, 11:04 am, Oli Charlesworth <ca...@olifilth.co.uk> wrote:
>>>> On Mar 12, 5:58 pm, "bharat pathak" <bha...@arithos.com> wrote:
>>>>> Hi,
>>>>>    I am seeing some negative group delay at
>>>>>    1000, 2000, 3000, 4000, 5000 Hz. The example
>>>>>    filter listed below with matlab/octave code.
>>>>>    any clue why this is happening? interesting
>>>>>    part is when I feed 1000 hz sine wave sampled
>>>>>    at 10000 hz I don't see the behaviour of
>>>>>    negative group delay.
>>>> Individual sine waves don't experience group delay, they experience
>>>> phase delay.
>>> Yes.  To see the group delay you will have to modulate your
>>> sine wave while staying completely within a bandwidth where
>>> the group delay is fairly constant, and then compare the
>>> before and after filtering locations of your modulation
>>> envelope.
>> No modulation needed. three signals close in frequency and amplitude
>> will produce beats that _look_ like modulation and illustrate the effect.
> 
> Well, I sort of agree.  But call any two of those sinusoids
> the sidebands produced by complex modulation of the third,
> and I think the sum is identical to a form of modulation
> with carrier.

Modulation (according to me) is a non-linear process (multiplication, 
rectification, etc). Summation is not. Both produce envelopes, but the 
details of those envelopes differ.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
0
jya (12871)
3/13/2008 2:03:04 AM
Reply:

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A veterinarian is urging farmers to share stories about their industry, to balance negative media.

IMF chief Christine Lagarde sees positive impact from negative rates
The world economy would be worse off without negative interest rates, according to International Monetary Fund managing director Christine Lagarde. ...

Kansas City Fed: Regional Manufacturing Activity "remained negative" in March
From the Kansas City Fed: Tenth District Manufacturing Activity Remained Negative The Federal Reserve Bank of Kansas City released the March ...

Negative "Batman v Superman" reviews get people talking
Negative "Batman v Superman" reviews get people talking

Resources last updated: 3/29/2016 11:28:32 PM