[PD] Notch filter
Claude HeilandAllen
claudiusmaximus at goto10.org
Wed Jan 23 15:19:14 CET 2008
yvan volochine wrote:
> Could someone explain me how I can make a notch with biquad~ (or with
> any other native pd objects) please ?
A notch filter is basically this in a zplane plot:

 o cos(a), sin(a)
 x r*cos(a), r*sin(a)

+

 x r*cos(a), r*sin(a)
 o cos(a), sin(a)

Where:
o = zero on unit circle
x = pole just inside unit circle
Parameters:
a = 2*pi*frequency/samplerate (zero+pole angle)
r = just less than 1 (pole radius)
The closer r is to 1, the narrower the notch is.
Pd objects:
samplerate~
czero~
cpole~
expr~  for accuracy
cos~  for speed, note cos~ expects 0..1 instead of 0..2PI
See also:
http://crca.ucsd.edu/~msp/techniques/latest/bookhtml/node144.html
Hope this helps,
Claude

http://claudiusmaximus.goto10.org
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