feature request: constant q transform

[vandenoever]

Constant Q Transform is a transformation for audio that uses a log scale for the frequency instead of a linear scale like FFT does. A fast implementation of Constant Q Transform uses FFT and a kernel.

https://en.wikipedia.org/wiki/Constant-Q_transform
http://academics.wellesley.edu/Physics/brown/pubs/effalgV92P2698-P2701.pdf

CQT is implemented in ffmpeg en mpv and gives intuitive visualization of which notes are being played at a given time.

https://trac.ffmpeg.org/wiki/FancyFilteringExamples#showcqt

[vandenoever]

There's already a crate for cqt, but it does not use the fast implementation with fft.

https://github.com/alexjago/cqt