KeyTrack | SuperCollider 3.14.0-dev Help

Description

A (12TET major/minor) key tracker based on a pitch class profile of energy across FFT bins and matching this to templates for major and minor scales in all transpositions. It assumes a 440 Hz concert A reference. Output is 0-11 C major to B major, 12-23 C minor to B minor.

Class Methods

KeyTrack.kr(chain, keydecay: 2.0, chromaleak: 0.5)

Arguments:

chain	[fft] Audio input to track. This must have been pre-analysed by a 4096 size FFT. No other FFT sizes are valid except as noted below.
keydecay	[sk] Number of seconds for the influence of a window on the final key decision to decay by 40dB (to 0.01 its original value).
chromaleak	[sk] Each frame, the chroma values are set to the previous value multiplied by the chromadecay. 0.0 will start each frame afresh with no memory.

Inherited class methods

Instance Methods

Inherited instance methods

Examples

/*
Research Notes:
See the MIREX2006 audio key tracking competition and Emilia Gomez's PhD thesis, Tonal Description of Music Audio Signals

The following code was used to create the datasets for the UGen, and would be the basis of extensions

Need one set of bin data for 44100 and one for 48000

KeyTrack calculations, need to make arrays of FFT bins and weights for each chromatic tone.
greater resolution, 4096 FFT, avoid lower octaves, too messy there

60*6*2 output arrays
*/

(
var fftN, fftBins, binsize;
var midinotes;
var sr;
var wtlist, binlist;

sr = 48000; //44100;

fftN = 4096;
fftBins = fftN.div(2);
binsize = sr / fftN;

midinotes = (33..92); // 60 notes, 55 Hz up to 1661.2187903198 Hz

wtlist = List[];
binlist = List[];

// for each note have six harmonic locations
midinotes.do{ |note|
    var freq, whichbin, lowerbin, prop;

freq = note.midicps;

6.do{|j|
        var partialfreq, partialamp;

partialamp = 1.0 / (j + 1);
        partialfreq = freq * (j + 1);

whichbin = partialfreq / binsize;
        lowerbin = whichbin.asInteger;
        prop = 1.0 - (whichbin - lowerbin);

binlist.add(lowerbin).add(lowerbin + 1);
        wtlist.add(prop * partialamp).add((1.0 - prop) * partialamp);

};

Post << (binlist) << nl<< nl;

Post << (wtlist) << nl<< nl;

binlist.size.postln;
wtlist.size.postln;
)

helpfile source: /usr/local/share/SuperCollider/HelpSource/Classes/KeyTrack.schelp
link::Classes/KeyTrack::

KeyTrack : UGen : AbstractFunction : Object