Subject: Re: [linux-audio-dev] Pitchshift/Timestretch project..
From: Cournapeau David (cournape_AT_enst.fr)
Date: Tue Apr 06 2004 - 13:01:33 EEST
I forgot to add that there is a matlab script which does the basic phase
vocoder stuff on musicdsp.org. As I am the one who writes this script, I
can help you if you have any questions ;). As the script only uses the
matlab language and fft, it should run on scilab and/or octave, but I
haven't tried myself.
cheers,
David
Cournapeau David wrote:
> Well, kind of. The idea of the phase vocoder, which more or less
> describes what you said,
> is to decompose each time-domain frame into N frequency bins, and to
> suppose that there is only one underlying stationary sinusoidal in
> each frequency canal. If this is the case, you unwrap the phase to
> have the frequency of the sinusoid, and you resynthetise it with a
> longer or shorter time frame.
>
> The problem is that it demands short windows (for the hypothesis one
> stationary sinusoid in each frequency canal to be valid), which means
> very poor frequency resolution. Basically, you have to make a trade
> off between time resolution and frequency resolution (nothing new here
> ;)). So the idea is to adapt the window size to the content of the
> signal, which means being able to detect the transient (which are
> better stretched with small windows)...
>
> J Bonada wrote his PhD on this subject, if you are interested:
>
> http://www.kug.ac.at/iem/lehre/arbeiten/hammer.pdf
>
> cheers,
>
> David
>
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