Fork Code: Paulstretch for SuperCollider

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(
SynthDef(\paulstretchMono, { |out = 0, bufnum, envBufnum, pan = 0, stretch = 50, window = 0.25, amp = 1|
	// Paulstretch for SuperCollider
	// Based on the Paul's Extreme Sound Stretch algorithm by Nasca Octavian PAUL
	// https://github.com/paulnasca/paulstretch_python/blob/master/paulstretch_steps.png
	//
	// By Jean-Philippe Drecourt
	// http://drecourt.com
	// April 2020
	//
	// Arguments:
	// out: output bus (stereo output)
	// bufnum: the sound buffer. Must be Mono. (Use 2 instances with Buffer.readChannel for stereo)
	// envBufnum: The grain envelope buffer created as follows:
	//// envBuf = Buffer.alloc(s, s.sampleRate, 1);
	//// envSignal = Signal.newClear(s.sampleRate).waveFill({|x| (1 - x.pow(2)).pow(1.25)}, -1.0, 1.0);
	//// envBuf.loadCollection(envSignal);
	// pan: Equal power panning, useful for stereo use.
	// stretch: stretch factor (modulatable)
	// window: the suggested grain size, will be resized to closest fft window size
	// amp: amplification
	var trigPeriod, sig, chain, trig, pos, fftSize;
	// Calculating fft buffer size according to suggested window size
	fftSize = 2**floor(log2(window*SampleRate.ir));
	// Grain parameters
	// The grain is the exact length of the FFT window
	trigPeriod = fftSize/SampleRate.ir;
	trig = Impulse.ar(1/trigPeriod);
	pos = Demand.ar(trig, 0, demandUGens: Dseries(0, trigPeriod/stretch));
	// Extraction of 2 consecutive grains
	// Both grains need to be treated together for superposition afterwards
	sig = [GrainBuf.ar(1, trig, trigPeriod, bufnum, 1, pos, envbufnum: envBufnum),
		GrainBuf.ar(1, trig, trigPeriod, bufnum, 1, pos + (trigPeriod/(2*stretch)), envbufnum: envBufnum)]*amp;
	// FFT magic
	sig = sig.collect({ |item, i|
		chain = FFT(LocalBuf(fftSize), item, hop: 1.0, wintype: -1);
		// PV_Diffuser is only active if its trigger is 1
		// And it needs to be reset for each grain to get the smooth envelope
		chain = PV_Diffuser(chain, 1 - trig);
		item = IFFT(chain, wintype: -1);
	});
	// Reapply the grain envelope because the FFT phase randomization removes it
	sig = sig*PlayBuf.ar(1, envBufnum, 1/(trigPeriod), loop:1);
	// Delay second grain by half a grain length for superposition
	sig[1] = DelayC.ar(sig[1], trigPeriod/2, trigPeriod/2);
	// Panned output
	Out.ar(out, Pan2.ar(Mix.new(sig), pan));
}).add;
)

// Example
({
	var envBuf, envSignal, buffer;
	buffer = Buffer.read(s, Platform.resourceDir +/+ "sounds/a11wlk01.wav");
	// The grain envelope
	envBuf = Buffer.alloc(s, s.sampleRate, 1);
	envSignal = Signal.newClear(s.sampleRate).waveFill({|x| (1 - x.pow(2)).pow(1.25)}, -1.0, 1.0);
	envBuf.loadCollection(envSignal);
	s.sync();
	// Runs indefinitely
	Synth(\paulstretchMono, [\bufnum, buffer.bufnum, \envBufnum, envBuf.bufnum]);
}.fork;
)

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