108 lines
2.9 KiB
Text
108 lines
2.9 KiB
Text
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#lang scribble/manual
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@(require (for-label racket))
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@title{StereoConvolution2L}
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Stereo real-time convolver with linear interpolation@section{categories}
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UGens>FFT, UGens>Convolution
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@section{related}
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Classes/Convolution, Classes/Convolution2L
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@section{description}
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Strict convolution with fixed kernel which can be updated using a trigger signal. There is a linear crossfade between the buffers upon change.
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Like link::Classes/Convolution2L::, but convolves with two buffers and outputs a stereo signal. This saves one FFT transformation per period, as compared to using two copies of link::Classes/Convolution2L::.
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Useful applications could include stereo reverberation or HRTF convolution.
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See Steven W Smith, The Scientist and Engineer's Guide to Digital Signal Processing, chapter 18: link::http://www.dspguide.com/ch18.htm::
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@section{classmethods}
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@section{method}
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ar
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@section{argument}
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in
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processing target.
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@section{argument}
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kernelL
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buffer index for the fixed kernel of the left channel, may be modulated in combination with the trigger.
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@section{argument}
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kernelR
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buffer index for the fixed kernel of the right channel, may be modulated in combination with the trigger.
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@section{argument}
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trigger
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update the kernel on a change from <= 0 to > 0.
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@section{argument}
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framesize
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size of FFT frame, must be a power of two (512, 1024, 2048, 4096 are standard choices).
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Convolution uses twice this number internally.
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Note that the convolution gets progressively more expensive to run for higher powers!
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The maximum value you can use is 2^16=16384.
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(This upper limit is half of "SC_FFT_MAXSIZE" defined in the SC source code.)
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Larger convolutions than this can be done using link::Classes/PartConv::.
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@section{argument}
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crossfade
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The number of periods over which a crossfade is made. The default is 1. This must be an integer.
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@section{argument}
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mul
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@section{argument}
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add
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@section{examples}
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@racketblock[
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(
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//allocate three buffers
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b = Buffer.alloc(s, 2048);
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c = Buffer.alloc(s, 2048);
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d = Buffer.alloc(s, 2048);
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b.zero;
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c.zero;
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d.zero;
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)
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(
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50.do({ |it| c.set(20 * it + 10, 1.0.rand); });
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3.do({ |it| b.set(400 * it + 100, 1); });
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20.do({ |it| d.set(40 * it + 20, 1); });
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)
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(
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SynthDef(\conv_test, { arg kernel1, kernel2, t_trig = 0;
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var input;
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input = Impulse.ar(1);
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// must have power of two framesize
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Out.ar(0, StereoConvolution2L.ar(input, kernel1, kernel2, t_trig, 2048, 1, 0.5));
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}).add
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)
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x = Synth(\conv_test, [\kernel1, b, \kernel2, c]);
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// changing the buffer number:
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x.set(\kernel1,d);
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x.set(\t_trig,1); // after this trigger, the change will take effect.
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x.set(\kernel2,d);
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x.set(\t_trig,1); // after this trigger, the change will take effect.
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d.zero;
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40.do({ |it| d.set(20 * it + 10, 1); });// changing the buffers' contents
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x.set(\t_trig, 1); // after this trigger, the change will take effect.
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x.set(\kernel1, b);
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x.set(\t_trig, 1); // after this trigger, the change will take effect.
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x.free;
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::
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]
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