[PD] reson~ from max in pd

[Björn Lindig]

Thank you Frank! Your information is very useful and interesting. I think, the 
jurney of learning how to make filters has just begun!

Best regards,

Bjoern

Am Mittwoch 10 März 2010 09:09:19 schrieb Frank Barknecht:
> Hallo,
> 
> Björn Lindig hat gesagt: // Björn Lindig wrote:
> > a friend asked me, wether there is a object similar to the [fffb~] in
> > max/msp (a "fast fixed filter bank") in pd. I did not find it instantly
> > so I started to build one after the formula posted in [reson~]s help in
> > max:
> > 
> > y[n] = gain * (x[n] - r * x[n-2]) + c1 * y[n-1] + c2 * y[n-2]
> > 
> > I appended a patch, that I created after this formula. The Problem is,
> > that I would love to klone the max-object, but at the moment I have only
> > inlets for r, c1, c2 and gain. What I need is the math to calculate the
> > values for r, c1, c2 and gain for given center frequency, Q/Bandwith,
> > and gain.
> 
> The equation above is the important base equation for many filters, but in
> practice it is pretty useless. The brains are in how to calculate the
> various parameters given more musical inputs like frequency and
> bandwith/resonance, and normalizing the output volume. Traditionally (i.e.
> since at least CSound times) what is called "reson" is a two-pole-two-zero
> (2nd order) resonating bandpass filter. In Pd an equivalent to equation
> above is a [biquad~] object or alternatively this:
> 
> 
>  [rzero~]
> 
>  [rzero~]
> 
>  [cpole~]
> 
>  [cpole~]
> 
> 
> with suitable transofrmations of the input parameters to get the pole/zero
> coefficients right.
> 
> > I started reading the chapters on time shifts and delays and filters in
> > miller-puckettes book and the book of J. O. Smith. But to be honest, I
> > did not yet understand much of what is writen there. So I thought, there
> > might be someone arround here, who can give me a fast answer, or who can
> > point me into the right direction.
> 
> I think, JOS and MSP are already the right direction, another stop could be
> the book at www.dspguide.com
> 
> > If it is the best to try resonz and resonr (I'm on train building
> > pd-extended, used vanilla before), I'll accept that.
> 
> I believe, resonz is the same as reson~ in Max/MSP. All these resonX things
> differ only in how they normalize the filter for different center
> frequencies. resonr keeps the resonance gain constant, resonz normalizes
> the peak gain:
> http://www.dsprelated.com/dspbooks/filters/Peak_Gain_Versus_Resonance.html
> 
> resonz~ and resonr~ can be build as abstractions, so there's no need to
> install externals just for them:
> http://lists.puredata.info/pipermail/pd-list/2008-12/067018.html
> 
> These and some more Pd vanilla filters are also part of the "rj" library:
> http://trac.rjdj.me/browser/trunk/rjlib/rj
> 
> Ciao