FFT overlap parameter in spectrogram?

Audacity 3 Help Forum
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Hi everyone,
I have a “simple” technical question about the spectrogram parameters in Audacity : we can change the length of the window (128, 256, 1024, etc), but we can not change the overlap value used to create the spectrogram. Some other softwares enable users to change that value but Audacity doesn’t. Now it isn’t really a problem for me, i’m okay with the fact that it is non modifiable, but for academic purposes i would like to know what is the overlap value that what chosen by Audacity developers.

This is a subject that was already brought up by other topics (e.g. Overlapping in FFT analysis or Spectrogram overlap? ) but surprisingly they didn’t get any definitive answer…!

I checked also in the manual (page for spectrogram_view and page for spectrogram_settings ) to see if that was indicated but i didn’t find the information.

Could anyone help me (someone from the dev team perhaps, or some on who knows how to retrieve this technical info ijn the sourcecode…?) ? Thanks !
Have a good day,
Gl0

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Last time I looked it used half window overlap.

3

Hi Steve,
Okay thanks for your fast answer.
I’m no specialist in FFT, but from what i gather, when you say that Audacity uses a half window overlap, it signifies that for one individual window, half of it will overlap with the last half of the previous window, and half of it will overlap with the first half of the following window (meaning that globally, all the windows except the first and the last ones will be 100% overlapped by their neighbouring windows).

Is that correct ?

Thanks ! Have a good day !

4

Yes, each window overlaps half of the previous and half of the following windows.
I believe the first window is actually a half window, overlapping the first half of the first full window:

windows

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Hello Steve, thank you for your answer and for the colorful description !

Would it be possible to add this information (about the overlap value) in the manual (e.g. in Spectrogram View - Audacity Manual or Spectrograms Preferences - Audacity Manual ), for future references, even if it’s just to write down the ‘hardwired’ information and to say that this parameter is not customizable ?
That would be nice for some interested users i think.

Thanks and have a good day and see you later perhaps !
Gl0

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I’m not sure that there will be a manual once Audacity 4 has been released. The manual is one of the remaining artefacts from when Audacity was developed by volunteers. I think the new Muse Group team favour their new support site. It would be better to address such questions directly to the Muse Group development team, though I’m unsure of the correct channel to contact them - perhaps via Discord or YouTube.

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