«Paulstretch for SuperCollider» by jpdrecourt

on 07 Apr'20 03:46 in ambientdronestretching

This is a port of the basic Paulstretch algorithm to SuperCollider (no onset detection). Mono version, for stereo, use 2 instances hard panned. The sound buffer needs to be mono too, so use Buffer.readChannel to extract separate channels. The stretch parameter is modulatable. That allows for phasing effects if using more than one instance.

Thanks to Paul for his feedback! Check his work at http://www.paulnasca.com/

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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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