[PD] [vcf~] and [biquad~] filters

julien.breval at tremplin-utc.net julien.breval at tremplin-utc.net
Mon May 17 19:56:08 CEST 2004


In June I will participate to a concert in which we all have to use Max/MSP. 
Therefore I am currently porting some of my Pd patches to MSP, and I have some 
problems with bandpass filtering.

In Pd, I use [vcf~]. I don't find any MSP filter that has a similar sound. 
With MSP filters like [svf~], [filtergraph] or [reson~], if you raise Q, you 
can still hear lots of frequencies that are only more or less attenuated. With 
[vcf~] some frequencies can disappear if you raise Q (actually, they are very 
much attenuated so you don't hear them). I prefer this sound.

The right solution sould be to use [biquad~]. MSP-[biquad~] looks like Pd-
[biquad~] with some arguments inversed. 
Unfortunately, besides a paper from Harmony Central I didn't find much 
information on it. Do you know any documentation about biquad filters ?

How do you make the simplest (linear) bandpass filter  using [biquad~] 
(parameters should be F and Q) ? I don't find any working conversion algorithm 
from (F,Q) to (bb1, bb2, ff1, ff2, ff3). 
I need something that resembles a '^' rather than a -90°rotated-'{', for any 
(Q,F) parameters  :) 

Thanks a lot


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