```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.
&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
```
```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.
```
```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.
&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
```
```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.

```
```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

```
```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);

```