The algorithm I would use to calculate BPM is to
  1. calculate the modulation envelope of the waveform using either a Hilbert transform or rectification and smoothing
  2. compute the Fast Fourier Transform (FFT) of the modulation envelope
  3. look for the strongest peak in the 0.2-5Hz range (depending on the music)
  4. Assign the center of the peak to be the BPM.
Note that most music is approximately scale-free (or fractal, to use a more popular term) so that there will be energy at all time scales. But for some kinds of music there will be a prominent peak in the above range that people usually associate with BPM.

How to do all of this in perl? I would use PDL. It is very efficient in manipulating vector quantities like sound waveforms and has a built in FFT function.

-Mark

In reply to Re: calculating the bpm of a song in mp3 format by kvale
in thread calculating the bpm of a song in mp3 format by keiusui

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