On 07.02.2011, at 00:12, Hans-Christoph Steiner wrote:

> 
> I've started to write a GUI for generating biquad coefficients (something 
> like Max/MSP's [filtergraph~]).  I've gotten the GUI interaction working 
> well, now I'm looking for the algorithms for generating a plot of the 
> frequency response of a given set of biquad coefficents?  It'll end up being 
> Tcl, but I can easily read C, Csound, Java, Perl, Python, etc.
> 
> .hc

i've been using the attached js file to query amplitude and phase response of 
biquad coeffs,
where the coeffs are expected to be of the form: y[n] = a0 * x[n] + a1 * x[n-1] 
+ a2 * x[n-2] - b1 * y[n-1] - b2 * y[n-2] (like in maxmsp).
so, you'd have to rearrage the coeffs and turn the sign of the fb coeffs to 
make it work with the pd biquad~.

vb

Attachment: queryBiquad.js
Description: JavaScript source



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