[PD] Resonant filter using cpole~ czero~
Mathieu Bouchard
matju at artengine.ca
Mon Feb 20 00:12:54 CET 2012
Le 2012-02-19 à 17:48:00, Mike Moser-Booth a écrit :
> On Sun, Feb 19, 2012 at 4:54 PM, Mathieu Bouchard <matju at artengine.ca> wrote:
>> Why would you change the signs of a and b but not c ?
>> (Was I giving the formula relative to ax²+bx+c=0 or did I assume ax²+bx=c by
>> accident ?)
>
> I think it has to do with where c is in the difference equation:
> c*y[n] = g*x[n] + a*y[n-1] + b*y[n-2]
This equation uses a for the middle term (y[n-1]) ? Weird.
I'd expect b to go with y[n-1], whereas a and c would go with either y[n]
or y[n-2]...
BTW, the equations I used are things that I reconstituted from the source
code of [biquad~] in pd/src/d_filter.c. They don't come from manuals.
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| Mathieu BOUCHARD ----- téléphone : +1.514.383.3801 ----- Montréal, QC
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