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 _______________________________________________ [email protected] mailing list UNSUBSCRIBE and account-management -> http://lists.puredata.info/listinfo/pd-list
