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