Hello all ! I'd like to make a 2pole notch filter. I found a few topics about notch filters on this list but I didn't understand everything. I read that I could make one with biquad~ but this object is somehow obscure to me. I don't know how to deal with the 5 parameters. In maxmsp, you have the filtergraph~ object which "translates" your Freq, Q and so on for use with biquad~ but in pd I just don't get it... The filtergraph pd objects are also difficult for me to understand. Could someone explain me how I can make a notch with biquad~ (or with any other native pd objects) please ? Thanks.
_y
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,
Claude
Thanx for your prompt answer Claude. I've read this on Puckette's book and other stuffs on the web, but my problem is how to implement those equations in pd's world ? Sorry if this sounds stupid... Best.
_y
On Wed, Jan 23, 2008 at 07:10:44AM -0800, yvan volochine wrote:
Thanx for your prompt answer Claude. I've read this on Puckette's book and other stuffs on the web, but my problem is how to implement those equations in pd's world ? Sorry if this sounds stupid...
I would also love to see a working example of a filter built from [cpole~] and friends. Anybody got links to something like that?
Best,
Chris.
-
Chris McCormick -
Claude Heiland-Allen -
yvan volochine