Most standard reverbs involve the use of a network of comb and allpass filters. The Schroeder model uses 4 comb filter in parallel and two cascading allpass filters like this,

comb1--
comb2---_____Allpass1__Allpass2 comb3---/ comb4--/

I have included a comb filter and allpass filter in the attached patch, in a comb filter the input signal is fed into a delay which is then feedback into the delay after being mmultipliedby a gain factor less than 1, anything over one will cause the filter to be unstable. An allpass filter is ssimilarbut there is no initial delay between the incoming and outputted signal, the signal goes straight through the filter but splits into two before being outputted, one of the signals is multiplied by -gain and sent straight to the output and the other goes into a delay line which is then ffed backinto the delay line after being multiplied by a +gain, the product of the -gain and +gain are added together then to form your ooutputsignal, this is why the allpass filter is unique in that it passes all frequencies equally, if that makes sense, anyway the patch will make it clearer, hopefully!

regards, Rory.

--- David Sabine dave@davesabine.com wrote: > Hello all,

Has anybody designed a multichannel reverb abstraction or external for PD (Windows version). To be honest, I'd like to build a 4-channel reverb myself but I'm having some difficulty understanding how such a thing is accomplished. Can anybody lend some help?

the multiverb~ (ala freeverb~ external) crashes my Windows XP.

Regards, Dave Sabine

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