Biquad Freq and phase response

rl · 26 Nov 2006

They provide a way to paint frequency and phase responses without using a FFT. The builtin Parametric EQ module uses them.

oddson · 28 Apr 2012

There was a followup post from 'rocko' here today... I hope I didn't delete is accidentally? 😕

If I did then this might help what I took his question to be.

My biquad knowledge -- limited and hard one -- is already getting rusty... So I may need to be corrected here!

All biquads work the same the only difference is coefficient naming (whether the feedback or feedforward coefficients are 'a' or 'b') and whether there is a gain parameter (i.e. there is both an a0 and a b0).

The analyzer primitives use 'a' for feed-forward:

and y(n) = a0*b0*x(n) + a1*b0*x(n-1) + a2*b0*x(n-2) - b0*b1*y(n-1) - b0*b2*y(n-2)

b0 will be 1 in most cases as it's just a gain parameter.