Difference between revisions of "Spectrograms"
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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. | 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: | + | Time runs from left to right, low frequencies are at the bottom and high ones at the top and the light at each point represents the energy in the sound at that frequency at a particular moment. |
| + | |||
| + | As well as helping us understand the internal structure of Delia's pieces, these also help us recreate conventional scores from her sound files, for example: | ||
* [[Fresh Aire (score)]] | * [[Fresh Aire (score)]] | ||
* [[The Pattern Emerges (score)]] | * [[The Pattern Emerges (score)]] | ||
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=Logarithmic frequency axis= | =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 | + | 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 just 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. |
| − | is logarithmic, which gives the same number of pixel rows per semitone. | ||
=Usage in the WikiDelia= | =Usage in the WikiDelia= | ||
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* number of pixel columns per second on the time axis (usually 50) | * 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, | + | {{Thumb|The Pattern Emerges - Spectrogram with grid}} |
| + | 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, see the example on the right. | ||
| − | Make a small donation and email <TT>delia.derbyshire.net@gmail.com</TT> attaching the sound file you would like analysed | + | Make a small donation and email <TT>delia.derbyshire.net@gmail.com</TT> attaching the sound file you would like analysed. |
=Software= | =Software= | ||
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A more precise technique would be to write a Constant-Q tranform directly instead of distorting a linear FFT.<ref>''[http://labrosa.ee.columbia.edu/matlab/sgram/ Spectrograms: Constant-Q (Log-frequency) and conventional (linear)]'' by Dan Ellis.</ref> | A more precise technique would be to write a Constant-Q tranform directly instead of distorting a linear FFT.<ref>''[http://labrosa.ee.columbia.edu/matlab/sgram/ Spectrograms: Constant-Q (Log-frequency) and conventional (linear)]'' by Dan Ellis.</ref> | ||
| + | |||
| + | There is another program that does log-frequency-axis spectrograms: the free audio editor Audacity (though they're nowhere near as beautiful as these!) | ||
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Revision as of 20:03, 3 December 2015
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.
Time runs from left to right, low frequencies are at the bottom and high ones at the top and the light at each point represents the energy in the sound at that frequency at a particular moment.
As well as helping us understand the internal structure of Delia's pieces, these also help us recreate conventional scores from her sound files, for example:
Contents
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 just 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, see the example on the right.
Make a small donation and email delia.derbyshire.net@gmail.com attaching the sound file you would like analysed.
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.[1]
There is another program that does log-frequency-axis spectrograms: the free audio editor Audacity (though they're nowhere near as beautiful as these!)
