Subject: Re: [linux-audio-dev] time-stretching filters (was: LADSPA Specs)
From: Likai Liu (news_AT_likai.net)
Date: Sat May 11 2002 - 22:59:32 EEST
Lance Blisters wrote:
>>I think the time-stretching plugin is a very legitimate example
>>
>
> I'm looking for a decent-sounding time-stretching algorithm.
> can anybody recommend one?
>
> By time-stretching i mean resampling to any rate, changing
> the audio speed with the corresponding shift in pitch, just
> like changing the speed of a turntable.
>
the double or drop sample approach is even more difficult to implement
than linear interpolation. I've written some quick and dirty floating
point linear interpolation, but unfortunately not in a plugin form
(because ... at least not for ladspa at this moment).
linear interpolation is good for most purposes, however, if you're
really concerned about quality, a second order spline interpolation
(with quadratic formula) sound like a good idea. I know that "sox" has a
more complicated resampling formula that works well with uniform noise too.
now to stretch the time and pitch independently is a bit difficult. my
idea is to apply a (cross-windowed) fft pitch shift first, and then
resample to get desired result. but i have not implemented this proof of
concept yet.
liulk
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