Convolution2 real-time convolver

Convolution2.ar(in, bufnum, trigger, framesize, mul, add)

Strict convolution with fixed kernel which can be updated using a trigger signal.

//see ch18 http://www.dspguide.com/ch18.htm Steven W Smith

in - processing target

bufnum - buffer index for the fixed kernel, may be modulated in combination with the trigger

trigger - update the kernel on a change from <=0 to >0

framesize - size of FFT frame, must be a power of two. Convolution uses twice this number internally, maximum value you can give this argument is 2^16=65536. Note that it gets progressively more expensive to run for higher powers! 512, 1024, 2048, 4096 standard.   

(//allocate three buffers

b = Buffer.alloc(s,2048);

c = Buffer.alloc(s,2048);

d = Buffer.alloc(s,2048);

b.zero;

c.zero;

d.zero;

)

(

50.do({ |it| c.set(20*it+10, 1.0.rand); });

3.do({ |it| b.set(400*it+100, 1); });

20.do({ |it| d.set(40*it+20, 1); });

)

(

SynthDef( "conv-test", { arg kernel, trig=0;

var input;

input=Impulse.ar(1);

//must have power of two framesize

Out.ar(0,Convolution2.ar(input,kernel,trig,2048, 0.5));

}).send(s)

)

x = Synth.new("conv-test",[\kernel,b.bufnum]);

// changing the buffer number:

x.set(\kernel,c.bufnum);

x.set(\trig,0);

x.set(\trig,1); // after this trigger, the change will take effect.

x.set(\kernel,d.bufnum);

x.set(\trig,0);

x.set(\trig,1); // after this trigger, the change will take effect.

d.zero;

40.do({ |it| d.set(20*it+10, 1); });// changing the buffers' contents

x.set(\trig,0);

x.set(\trig,1); // after this trigger, the change will take effect.

x.set(\kernel,b.bufnum);

x.set(\trig,0);

x.set(\trig,1); // after this trigger, the change will take effect.

////next example

b = Buffer.read(s,"sounds/a11wlk01.wav");

(

{ var input, kernel;

input=AudioIn.ar(1);

//must have power of two framesize

Out.ar(0,Convolution2.ar(input,b.bufnum,0,512, 0.5));

}.play;

)

//another example

(

//must have power of two framesize- FFT size will be sorted by Convolution2 to be double this

//maximum is currently a=8192 for FFT of size 16384

a=2048;

s = Server.local; 

//kernel buffer

g = Buffer.alloc(s,a,1);

)

(

g.set(0,1.0);

100.do({arg i; g.set(a.rand, (i+1).reciprocal)});

)

(

//random impulse response

{

var input,inputAmp,threshhold,gate;

input = AudioIn.ar(1); 

inputAmp = Amplitude.kr(input);

threshhold = 0.02; // noise gating threshold

gate = Lag.kr(inputAmp > threshhold, 0.01);

Out.ar(0,Convolution2.ar(input*gate,g.bufnum,0, a, 0.5));

}.play;

)

//one last example

(

b = Buffer.alloc(s, 512, 1);

b.sine1(1.0/[1,2,3,4,5,6], true, true, true);

)

(

{ var input, kernel;

input=AudioIn.ar(1);

//must have power of two framesize

Out.ar(0,Convolution2.ar(input,b.bufnum,0, 512, 0.5));

}.play;

)