Spectrograms

Spectrograms are used in the WikiDelia to visualise the sonic content of Delia's pieces, and all the ones I have done are listed in the Audio page.

As well as helping understand Delia's pieces, these also help us recreate conventional scores from sound files:

• Fresh Aire (score)
• The Pattern Emerges (score)
• Moogies Bloogies (score)

Logarithmic frequency axis

The spectrograms used in the WikiDelia are not the usual kind, where the Y axis represents the linear frequency scale from 0 to 22050Hz and in which the top half of the graphic represents only the top octave of the sound, with all the musical detail crushed into the bottom few pixels. Here, the vertical scale is logarithmic, which gives the same number of pixel rows per semitone.

Usage in the WikiDelia

The spectrogram of a piece goes in three places:

• On the piece's page in a section Spectrogram usually just above Availability so that the Listen button is near.
• In the Audio page
• in delia-derbyshire.net/spectrograms

For example the piece Air has File:Air.ogg and File:Air - Spectrogram.jpg, used by the MediaWiki macros {{Spectrogram|Air - Spectrogram}} and {{Spectrogallery|Air}}

Get spectrograms of your music!

I am happy to run the log spectrum analyser on your music. You can specify:

• lowest pitch (usually A0, 27.5Hz)
• number of octaves (usually 9, to 14080Hz)
• number of pixels per semitone on the frequency axis (usually 8)
• number of pixel columns per second on the time axis (usually 50)

Optionally the software can superimpose single-pixel black and white lines at the frequencies of the piano keys and three-pixel-wide white lines at the positions of the manuscript stave lines, for example

Make a small donation and email delia.derbyshire.net@gmail.com attaching the sound file you would like analysed. Alternatively, I gather that there is a similar function in the free audio editor Audacity.

Software

The WikiDelia's spectro-analyser was written specifically for it, using a modified version of sndfile-spectrogram and an ImageMagick script to distort the image giving it a logarithmic frequency axis.

A more precise technique would be to write a Constant-Q tranform directly instead of distorting a linear FFT.