group delay

[Duane Wise]

Hello:

>   Mmm, as I see you have quite a lot of knowledge in DSP theory, let me
>ask you some help in digital filters ;-)
>How can you calculate the group delay of a recursive filter given its
>coefficients? (I mean, a practical computational algorithm...)
>I need it to implement that filter in a waveguide and then compensate
>for its delay in the waveguide lenght... but I have not enough time to
>look at those wonderful DSP books ... so if you were kind enough...

I put the coefficients of a single biquad (a1,a2,b0,b1,b2) into your
problem and derived a formula for its group delay.  The formula is over a
page long.  I would say that group delay is best calculated numerically.
That is, take the FFT phase of the filter's impulse response and
numerically differentiate the sequence.


Enjoy, Duane Wise (dwise at wholegrain-ds.com)