[PD] algorithms for drawing filter response curves

[Mathieu Bouchard]

On Sun, 6 Feb 2011, 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.

I made a rather simple patch that measures the frequency response of any 
linear filter of your choice (convolution, lop, hip, bp, biquad, etc.) by 
using FFT. I demonstrated it at Pd Convention 2007.

   http://gridflow.ca/gallery/operator_spectrum.png

except it only works for image filters, not sound.

It plots an image filter's spectrum like a topographic map for all 
combinations of horiz-frequencies and vert-frequencies at once. (however, 
it assumes that the effect is wrap-around, just like a FFT is wrap-around)

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| Mathieu Bouchard ---- tél: +1.514.383.3801 ---- Villeray, Montréal, QC