Qitch | SuperCollider 3.12.2 Help

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.

NOTE: You must load one of the auxilliary data files into a Buffer and pass the bufnum to the routine. These files take the form:

QspeckernN1024SR44100.wav
QspeckernN2048SR44100.wav
QspeckernN4096SR44100.wav
QspeckernN8192SR44100.wav
QspeckernN2048SR48000.wav
QspeckernN4096SR48000.wav

Only use the one for your output sampling rate. Bigger N means more stability and resolution but longer delay and higher average CPU cost. N= 2048 is a good tradeoff if you don't want to track over 1000Hz fundamentals. The 48000 SR files are untested and provided without any promises.

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

Qitch.kr(in: 0.0, databufnum, ampThreshold: 0.01, algoflag: 1, ampbufnum, minfreq: 0, maxfreq: 2500)

Arguments:

in	the audio rate input signal
databufnum	you must provide the initialisation data required by Qitch. This in the form of a .wav file that must be loaded to a buffer (see examples below). The data files should have come with this UGen.
ampThreshold	Qitch outputs a 0 in hasFreq if the input amplitude is below this threshold. Same as original Pitch.
algoflag	0 means use just the constant Q template pattern matcher. 1 flags the refinement based on the phase estimate.
ampbufnum	you may provide an 11 component buffer with template amplitudes- see example below.
minfreq	minimum output frequency in Hz
maxfreq	maximum output frequency in Hz

Inherited class methods

Instance Methods

Inherited instance methods

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); )

helpfile source: /usr/local/share/SuperCollider/Extensions/SC3plugins/PitchDetection/HelpSource/Classes/Qitch.schelp
link::Classes/Qitch::

Qitch : MultiOutUGen : UGen : AbstractFunction : Object Extension