A histogram of pitch classes

Chroma is an audio analysis that models the composition of pitch classes in a sound. In this context, a pitch class are bins of the spectrum derived through an FFT. By default, the Chroma algorithm will return 12 pitch classes, which conveniently maps on to a western model of tonal harmony (C, C#, D, D# etc…). The number of pitch classes can be changed, allowing you to tune the algorithm to return more or less granular bins in terms of what pitch class they represent.

Smoothing: 50 frames

Chroma is not a fundamental pitch tracker and won’t tell you about the structure of pitch classes, only their relative strength to each other. Furthermore, the entire spectrum is wrapped into a single octave, meaning any notion of register is lost. As such it is useful for perhaps identifying rough tonal components a sound might be comprised of, but nothing about their relationship to each other as a chord.