MatchingP

Extension

Description

This UGen analyses frames of input audio, a bit like FFT does, but using the assumption that most of the energy in each audio frame can be represented as a combination of a small number of "atoms". This is achieved using Matching Pursuit, which is a standard technique in the field of sparse representations.

You must supply a "dictionary" of atoms, given as a Buffer. Each channel of the Buffer is one atom (this means the atoms all have to be the same length - but zero-padding is OK).

This analysis is less efficient than FFT, so be careful of your CPU usage, and use small, short dictionaries if possible. It also outputs a lot of multichannel data.

Class Methods

.ar

.kr

Examples

In this example we make a simple dictionary which happens to be quite similar to an un-windowed FFT basis, and then analyse it.~dictlen = 128; ~dictsize = 64; ~dictarr = ~dictsize.collect{|i| sin(2pi*(i+1)*(1..~dictlen)/~dictlen) }; ~dictarr = ~dictarr.collect{|a| a / a.squared.sum.sqrt } // Here is where we L2 normalise all the atoms // The dictionary buffer: ~dict = Buffer.loadCollection(s, ~dictarr.flop.flat, ~dictsize); ~dict.plot // We'll output the activations to a bus too ~ntofind = 2; ~actbus = Bus.audio(s, ~ntofind * 2); ( x={ var son, outputs, trig, residual, acts, indices, magnitudes, resynth, delayedson; // Try one of these: son = Pulse.ar(200 * SinOsc.kr(0.3).exprange(0.9, 1.1)); //son = PinkNoise.ar * LFPulse.kr(1); //son = (PlayBuf.ar(~dictsize, ~dict, MouseX.kr(0.1, 2, 1). loop: 1) * ([0.1, 0.3, 0.5]++{0}.dup(~dictsize-3))).sum; outputs = MatchingP.ar(~dict, son, ~dictsize, ntofind: ~ntofind); trig = outputs[0]; residual = outputs[1]; acts = outputs[2..]; Out.ar(~actbus, acts); // In the next part we'll resynthesise the sound. // But you might like to mangle the 'acts' data to apply interesting FX: # indices, magnitudes = acts.clump(2).flop; // This makes it a bit convenient to apply manipulations //magnitudes = magnitudes.collect{|a| a * 3 * SinOsc.ar(exprand(0.1, 10))}; //magnitudes = magnitudes.collect{|a| a * 3 * SinOsc.ar(LFNoise1.kr(10).exprange(0.1, 10))}; //magnitudes = magnitudes.collect{|a| DelayN.ar(a, 0.1, LFNoise1.kr(0.1).range(0, 0.1))}; //magnitudes = magnitudes.reverse; //indices = ~dictsize - indices; acts = [indices, magnitudes].flop.flat; // reconstruct resynth = MatchingPResynth.ar(~dict, 0, trig, residual, *acts); delayedson = DelayN.ar(son, delaytime:BufDur.ir(~dict)); //Amplitude.ar(resynth - delayedson, 0.1, 1).poll(1, "amplitude of reconstruction error"); [delayedson * 0.0001, resynth * 0.1]; }.play ) ~actbus.scope s.scope