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There is a range of computer programs that can represent acoustic energy graphically in a spectrogram. I usually use Praat, which uses a black and white gradient to represent the intensity of energy at specific frequencies and time points. Here's an example: Praat black and white spectrogram

Often I find colour easier to interpret: colour spectrogram

Q: Can anybody suggest free software that produces online colour gradient spectrograms?

Solutions that I have considered:

  • Save Praat spectrogram, load into image processing software and replace black and white with colour gradient: too complicated
  • Use Audacity: Audacity can display colour spectrograms, but the resolution is nowhere as good as in Praat and no combination of options (window size and function) seems to improve that. Here's an example: Audacity colour spectrogram

(Note that the latter spectrogram is wide-band and the first in Praat narrow-band, but changing wide-band to narrow-band doesn't solve the problem in Audacity).

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WaveSurfer lets you display spectrograms in color, and it's free.

Once you record or import a sound, right-click (or the equivalent) on the waveform pane. Select Create Pane > Spectrogram. The spectrogram will appear in black and white as a default. Right-click (or the equivalent) on the spectrogram and select Properties. Here you can play with all different parameters, including the spectrogram color.

Below are two versions of the same spectrogram produced in WaveSurfer--one in black and white and the other in color:

black-and-white-spectrogram

color-spectrogram

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Bartlomiej Plichta has written a Praat script which automates your first solution, shelling out to the open-source ImageMagick package to do the colour conversion: http://bartus.us/blog/?p=579

Along the lines of your second solution (using something other than Praat): There were a fair number of free and commercial acoustic analysis programs around before Praat essentially obliterated the ecosystem, some of which could draw colour spectrograms. A free one that isn't dead yet is Wavesurfer: http://www.speech.kth.se/wavesurfer/

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  • Thanks Kevin! Have you tried Bartlomiej's script? He doesn't seem to be active any more and I encountered a problem with running the tricolorize batch script he linked to. I can't run it from the command line let alone from Praat. The directory it's in is in my PATH, but it throws up a couple of errors (suchas '#' and 'PROGNAME' not being recognised as commands). (Wavesurfer works fine, though!)
    – robert
    Sep 2 '13 at 16:15
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Sonic Visualiser is one of the programs I've been using to view/analyze my audio. It is freeware but it's a pretty decent prog imo. It does have many options to adjust your Spectrogram and a couple other options to get creative with. I mostly use it to listen to my techno tracks ;)

RingModulated Synth Pitch Down Filtered Out

Another nice option this prog has is where ever you put your mouse over gives you a dialog box in terms of Time, Frequency, Pitch & Phase.

A rap i recorded today

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Overtone Analyzer is another program that you might consider for color spectrograms. It provides a number of different color schemes:

Spectrogram of speech

It is optimized for high resolution spectrograms that are rendered in real time from recorded sound or from existing files. There are free and commercial versions available. The program has an integrated vowel chart and special features for formant analysis of vowels.

Disclaimer: I'm the author of this program and make my living from it.

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