Qitch

Extension

Description

This alternative pitch follower works in the frequency domain rather than Pitch's time domain correlation. Tradeoffs are made between latency and frequency resolution. It is meant to provide a relatively stable resultant tracked pitch based on a harmonic template.

In technical terms, this UGen calculates an FFT, applying Brown and Puckette's efficient constant Q transform on a quartertone scale, base note F3= 174.6Hz. Cross correlation search leads to the best match for a harmonic spectrum grid with falling amplitude components. A further fine tuning takes place based on instantaneous frequency estimation (rate of change of phase) for the winning FFT bin.

The algorithms are based on the following papers:

Judith C. Brown and Miller S. Puckette, 1992, "An efficient algorithm for the calculation of a constant Q transform". Journal of the Acoustical Society of America. 92(5); 2698-701.

Judith C. Brown, 1992, "Musical Fundamental Frequency Tracking Using a Pattern Recognition Method". Journal of the Acoustical Society of America. 92(3); 1394-402.

Judith C. Brown and Miller S. Puckette, 1993, "A High-Resolution Fundamental Frequency Determination Based on Phase Changes of the Fourier Transform". Journal of the Acoustical Society of America. 94(2); 662-7.

Class Methods

.kr

Examples

(use headphones!)s = Server.local; //assumes data file is in SC home application directory; else provide full path b = Buffer.read(s, "QspeckernN4096SR44100.wav"); //this line is absolutely essential! You must load the data required by the UGen! b.numFrames //it's not that much data ( a= SynthDef("testqitch",{arg infreq=440; var in, freq, hasFreq, out; in=SinOsc.ar(infreq); # freq, hasFreq = Qitch.kr(in, b.bufnum,0.01,1); Out.ar(0,[SinOsc.ar(freq,0.1),in]); }).play(s); ) a.set(\infreq,237); c=Buffer.read(s,"/Volumes/data/audio/nikkisitar/warmup.wav"); //sitar test file, try anything you have on your disk c.numFrames ( //sample tracking SynthDef("pitchFollow1",{ var in, amp, freq, hasFreq, out; in = PlayBuf.ar(1,c.bufnum, loop:1); amp = Amplitude.kr(in, 0.05, 0.05); # freq, hasFreq = Qitch.kr(in, b.bufnum, 0.1,1, -1,261, 800 ); out = Mix.new(VarSaw.ar(freq * [0.5,1,2], 0, LFNoise1.kr(0.3,0.1,0.1), amp)); Out.ar(0,[out,in]) }).play(s); ) b = Buffer.read(s, "QspeckernN2048SR44100.wav"); //quicker response with this data set d = Buffer.alloc(s,11); //make an amp template d.setn(0, [1,0.98,0.92,0.88,0.84,0.8,0.76,0.72,1.68,1.64,1.6]); //must have 11 components //analogous to example in the Pitch helpfile ( SynthDef("pitchFollow1",{ var in, amp, freq, hasFreq, out; in = Mix.new(SoundIn.ar([0,1])); amp = Amplitude.kr(in, 0.05, 0.05); # freq, hasFreq = Qitch.kr(in, b.bufnum, 0.02, 1, d.bufnum, 160, 880); //freq = Lag.kr(freq.cpsmidi.round(1).midicps, 0.05); out = Mix.new(VarSaw.ar(freq * [0.5,1,2], 0, LFNoise1.kr(0.3,0.1,0.1), amp)); 6.do({ out = AllpassN.ar(out, 0.040, [0.040.rand,0.040.rand], 2) }); Out.ar(0,out) }).play(s); )