PV_ExtractRepeat | SuperCollider 3.12.2 Help

Description

If you have a signal that consists of some fixed looping audio (e.g. a beat) plus some varying content (e.g. singing), this UGen uses a simple binary-masking technique to try and separate the looping bit from the non-looping bit. The quality of the separation is quite rough, but useful in some circumstances.

Note that this unit estimates the loop characteristics online in real time, meaning it takes a few times through the loop before the separation really kicks in. This means that at any point, any novel element is included in the nonrepeating part, even if it's really a loop that's starting.

You must know the loop duration - this unit will not estimate it for you.

Class Methods

PV_ExtractRepeat.new(buffer, loopbuf, loopdur, memorytime: 30, which: 0, ffthop: 0.5, thresh: 1)

Arguments:

array	The array of input signals.
chain	an fft chain
loopbuf	a buffer where data about the loop is calculated/stored. num frames should be enough to hold the loop (you'll get a warning if not), num channels should be (fftsize/2 + 1).
loopdur	duration in seconds of the bit you want extracted. (You can change the loop duration on-the-fly but you'll get some unhelpful results while the unit settles in to the new loop duration.)
memorytime	how quickly (in seconds) the recursive estimation converges
which	set to 0 to extract the loop, set to 1 to extract everything else
ffthop	this should match the hop size used in the FFT. typically 0.5.
(thresh)	threshold for allocating bins to repeating/nonrepeating. Default is 1, and raising it means more gets allocated to the repeating part.

Inherited class methods

Instance Methods

Inherited instance methods

Examples

First a toy example with synthetic material; then an example reading a WAV file from disk (you'll have to find one, and also find its bpm).s.boot // Create audio containing repeating and varying components, merged in the same channel: ( x = { var trigs, looplen = 2, loopy, varying; trigs = Impulse.kr(6/looplen) + Impulse.kr(4/looplen); loopy = BPF.ar(WhiteNoise.ar * EnvGen.ar(Env.perc(0.01, 0.3), trigs), LFCub.kr(1/looplen).exprange(100, 5000)); varying = Pulse.ar(LFNoise0.kr(6/looplen).exprange(100, 500).cpsmidi.round.midicps) * 0.1; (loopy + varying).dup }.play; ) // Now the thing that will attempt to separate them out again (inc a buffer for it to use): ~loopbuf = Buffer.alloc(s, 200, 513); ( y = { |which=1, active=1| var son = In.ar(0); var chain = FFT(LocalBuf(1024), son); chain = PV_ExtractRepeat(chain, ~loopbuf, 2, memorytime:30, which:which); ReplaceOut.ar(0, Select.ar(active, [son, IFFT(chain)]).dup); }.play(x, addAction: \addAfter); ) y.set(\which, 0) // focus on the nonrepeating bit y.set(\which, 1) // focus on the repeating bit y.set(\active, 0) // back to normal y.set(\active, 1) // filter it again y.free; x.free; ////////////////////////////////////// // With music: ~track = "~/tmpwavs/Postal Service - Such Great Heights.mp3.2.wav".standardizePath; ~bpm=116.6; ~track = "~/tmpwavs/Amy Winehouse - Rehab.mp3.wav".standardizePath; ~bpm=145.1; ~looplen = 480/~bpm; b = Buffer.cueSoundFile(s, ~track, 0, 2); x = { DiskIn.ar(2, b) }.play; // Now the thing that will attempt to separate them out again (inc a buffer for it to use): ~loopbuf = Buffer.alloc(s, 1000, 513); ( y = { |which=1, active=1, thresh=1| var son = In.ar(0); var chain = FFT(LocalBuf(1024), son); chain = PV_ExtractRepeat(chain, ~loopbuf, ~looplen, memorytime:30, which:which, thresh:thresh); ReplaceOut.ar(0, Select.ar(active, [son, IFFT(chain)]).dup); }.play(x, addAction: \addAfter); ) y.set(\which, 0) // focus on the nonrepeating bit y.set(\which, 1) // focus on the repeating bit y.set(\active, 0) // back to normal y.set(\active, 1) // filter it again y.set(\which, 0, \thresh, 1.5) // trying a higher threshold y.free; x.free; b.close

This unit is (c) Dan Stowell, based on the technique presented in this paper (but different - adapted for online estimation and with some other little differences):

Zafar Rafii and Bryan Pardo. "A Simple Music/Voice Separation Method based on the Extraction of the Repeating Musical Structure," 36th International Conference on Acoustics, Speech and Signal Processing (ICASSP 2011), Prague, Czech Republic, May 22-27, 2011. http://www.cs.northwestern.edu/~zra446/research.html

helpfile source: /usr/local/share/SuperCollider/Extensions/SC3plugins/MCLDUGens/HelpSource/Classes/PV_ExtractRepeat.schelp
link::Classes/PV_ExtractRepeat::

PV_ExtractRepeat : PV_ChainUGen : WidthFirstUGen : UGen : AbstractFunction : Object Extension