[PD] biquad~ with elementary filters [was: Re: dinosaurs ...]

Damian Stewart damian at frey.co.nz
Mon Sep 15 13:00:18 CEST 2008

Claude Heiland-Allen wrote:

> http://ccrma.stanford.edu/~jos/filters/BiQuad_Section.html
> you need to munge the biquad coefficients from the form expected by Pd's 
> biquad~ to the form of the difference equation at the bottom - should 
> just be some scaling and sign stuff.
> then you can factorize the transfer function's numerator and denominator 
> to get the locations of the (complex) zeroes and poles (using the 
> quadratic formula would do the trick)
> then feed them to [czero~] [cpole~], and an additional [*~] for the 
> global gain.

wow - this is a bit above my head at the moment. i can go from equations in 
C to pd, but only if i have the equations themselves to look at...

anyway it would be great to have a pure-pd [biquad~] with signal input. 
it's the resonance and ability to control the Q that i'm really after, plus 
the ability to nice tricks (cf [hlshelf] which combines a high and low 
shelf filter into one [biquad~], saving cpu). [lop~] and [hip~] do the 
trick for simple filtering but when you want a squelchy resonant lowpass 
for bass triangle wav filtering, they don't cut it..

damian stewart | skype: damiansnz | damian at frey.co.nz
frey | live art with machines | http://www.frey.co.nz

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