Group delay compensation in linear filter

[purnapragna]

matlab group delay compensation

hi all,
i am struck with problem of designing a linear filter based on given input and output. I doo not know how to compensate the group delay introduced by the filter. can anybodyhelp me in this regard?

purna!

 

[tiger_shark]

group delay compensation allpass filter

As you know, FIR filters have inherently linear phase so no compensation is needed.

For IIR, if you have the filter in MATLAB, you can use iirgrpdelay function in MATLAB and generate an all-pass filter with a desired groupdelay. Now, if your desired groupdelay is inverse of the IIR groupdelay, then , wehn you add the IIR + ALLPass together, you 'll get "almost" linear groupdelay.

Hope that works for you.
Regards -TS

 

[Kral]

Re: group delay compensation

purnapragna,
I'd like to expand a bit on the reply from tiger_shark. It is true that FIR filters can have linear phase. However, this is not always the case. One way to guarantee phase linearity is to use an odd number of coefficients, and ensure that the coefficients are symmetrical about the center coefficient. For example, if the coefficients are c0, c1, c2, c3, c4, then the following condition guarantees phase linearity.
c0 = c4
c1 = c3
There are other conditions that can guarantee either phase linearit or constant group delay. See, for example, the classic text by Rabiner and Gold, "Theory and Applications of Digital Dignal Processing".
Regards,
Kral