Friday, 17 August 2012

Audio spectrograms with a logarithmic frequency axis

I've wanted to do this since 1990.

The Pattern Emerges by Delia Derbyshire

Detail of start of melody and chords
Audio spectrograms with a logarithmic frequency axis turn a piece of music into a picture in which the musical notes are evenly spaced up the y axis from the bass notes at the bottom to the accompaniment and melody at the top. Time runs from left to right and the colours show how much energy there is in the sound at each frequency at each instant.

This makes it simple to score a piece accurately when only its audio survives.

It's made by warping a linear spectrogram created by the sndfile-spectrogram program in sndfile-tools using ImageMagick's -fx operator.

For further details and to listen to the above piece against its spectrogram, see

Update 2016-02-22: I've modified sndfile-spectrogram to enable it to produce log-frequency-axis spectrograms directly, now included in the master version of sndfile-tools.