gab
09-18-2006, 05:27 PM
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 17 samples.
But it not what I obtain! I have made a lot of tests with different inpu
frequency in the range [0...fs/2] and I always get a smaller delay tha
what I should expect from the group delay response of the filter.
Does anyone have an explaination to provide me?
It sounds to me really basic and I am really wasting my time with it!!!
Thanks for your help
Gabriel
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 17 samples.
But it not what I obtain! I have made a lot of tests with different inpu
frequency in the range [0...fs/2] and I always get a smaller delay tha
what I should expect from the group delay response of the filter.
Does anyone have an explaination to provide me?
It sounds to me really basic and I am really wasting my time with it!!!
Thanks for your help
Gabriel