Re: [linux-audio-dev] resampling

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Subject: Re: [linux-audio-dev] resampling
From: Paul Winkler (slinkp_AT_ulster.net)
Date: ke elo    18 1999 - 01:02:15 EDT


est_AT_hyperreal.org wrote:
>
(snip)
> Me too! I haven't even tested what quadratic (I assume that comes
> under `Lagrange-polynomial'?) gets me over linear.

I'm too ignorant to know the difference between all these algorithms by
name. But a while ago, out of curiosity, I did some testing of Csound's
interpolation routines. I just compared the output quality of a really
small function table (like, 8 points) sampled by oscil (no
interpolation), oscili (linear), and oscil3 ("a cubic interpolation
algorithm" -- is that related to "quadratic"? I stopped taking math
after 10th grade... too lazy, I guess... jazz band was more fun at the
time).

oscil3 sounded by far the best of the three. I used snd to see what the
output waveforms looked like. Visual inspection of the waveforms showed
that oscil was faithfully making great big stair-steps; oscili was
drawing straight line segments just like you would expect; and oscil3's
output sure looked a lot like a perfect sine wave. The difference in
audible noise level between oscili and oscil3 was pretty dramatic (but
then, I started with garbage).

> Eli Brandt discourseth:
> > An interesting comparison of sox's implementation of linear, sinc, and
> > polyphase resampling:
> > http://eakaw2.et.tu-dresden.de/~andreas/resample/resample.html
>
> Thanks for pointing this out.

Yeah! This is a great link for the audio-quality-HOWTO. Looks like Sox
can finally do decent-quality resampling!

-- 

---------------- paul winkler ------------------ slinkP arts: music, sound, illustration, design, etc.

zarmzarm_AT_hotmail.com --or-- slinkp AT ulster DOT net http://www.ulster.net/~abigoo/ ======================================================


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