23 Jan
2008
23 Jan
'08
3:19 p.m.
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 z-plane 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/book-html/node144.html
Hope this helps,