Forums > MaxMSP

coefficients for biquad~

May 22, 2010 | 6:38 pm

Hi,
I’m trying to use biquad~ without the filtergraph~ (so I can cotrol it with a midi controller) by inputing the minimum and maximum coefficients I get from the list of coefficients coming out from filtergraph~’s left outlet, in biquad~’s 3rd, 4th, 5th and 6th inlets, through a zmap object (so I can scale the controller’s values).
The result I get though, is not at all the same as if I use filtergraph. Am I doing something wrong?
Thanks,
Alex


May 22, 2010 | 10:46 pm

 
for sure, because minimum and maximum is not enough, it is not at all linear.

the picture below shows one way how to calculate the coefficients for a pass
filter (which i think is similar to what filtergraph does.)

usually you will prefer an interpolated/smoothed signal as input for [biquad~],
which is why you should look into [filtercoeff~].

pre maxmsp 4.3 users can use [hr.filtercoeff~] … or embed a small [filtergraph~]
object in an abstraction.
 

[attachment=133094,579]

Attachments:
  1. passcoeff.jpg

May 23, 2010 | 6:57 pm

The coefficients for biquad~ are interdependent, and they are calculated by filtergraph~ (or filtercoeff~) based on the filter type, gain, frequency, and Q you provide. So you should use your MIDI controllers to control those parameters, and feed those to filtergraph~ or filtercoeff~. To avoid clicks, you’ll probably want to interpolate between changes using line~ or number~, as shown in this example.

http://music.arts.uci.edu/dobrian/IAP2010/examples.htm#Ex20


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