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Python script that creates a chromagram from an audio file and then renders that chromagram to MIDI
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Chroma to MIDI

A simple module to create a chromagram from an audio file and then render that chromagram to MIDI

A hack started at CCRMA Summer MIR 2016: compute a chromagram, then sort the resulting array by its the 3 strongest values (tonal centers, more or less) and then write a MIDI file with "chroma-chords" at velocities 127, 64, and 1 respectively.

So, the MIDI file generated is a 3 note chord starting from C3 (aka middle c), with the 127 velocity note representing the strongest chroma, 64 the second strongest, 1 the third strongest. The chord duration is continuous as long as the chroma strength stays the same, and only makes a new chord if the chroma strength changes.

It works a little better if you input the tempo, which you can find by listening and tapping it out here or automatically estimate it in Python using Librosa or with Madmom Madmom (among other packages).

Uses Madmom's DeepChromaProcessor to create the Chromagram and then C Raffel's pretty_midi to print the MIDI file.

Example usage for creating a chromagram and then generating a MIDI file, from the root directory of the repo:

$ cd chroma_to_midi
$ python <path_to_audio> <path_to_midi> <tempo>

An example of the output is included in the repo, kanaya_base_salt.mid, which is a chroma-to-MIDI representation of the song 'Salt' by Kanaya Base (right click, save target as to download) from Lady Boy Records (Reykjavik, IS), used with permission ;)


Thanks for the help:

Steve Tjoa, Jeff Scott, James Jannicelli

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