A key mode tracker where output 0 = major, 1 = minor, 2 = chromatic (cluster).
Based on a pitch class profile of energy across FFT bins, matching this to templates for major, minor and 7 note cluster chromatic scales in all transpositions. It assumes a 440 Hz concert A reference. The winning mode is based on the strength of the match, e.g. maximal correlation with key profiles for either major, minor or chromatic cluster (appropriately normalised to a probability distribution summing to 1.0).
[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.
[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).
[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.