Subject: Re: [linux-audio-dev] Resampling
From: Alexander Ehlert (alexander.ehlert_AT_uni-tuebingen.de)
Date: Thu Aug 02 2001 - 11:47:08 EEST
Hi,
> OK. I have been quite skeptical to any FFT analysis/synthesis because
> the phase vocoder in Csound sounds very muddy even no change is done.
> But if you're handling only the complex values got from FFT (not amplitude-
> phase versions), then everything should be better.
For my ears it sounds really good. The only thing for upsampling I do is
padding zeroes for higher frequencies, or dropping out frequencies
for downsampling. I don't see any problems here. Ok, there might be
more performant algorithms in time space representation, but I see
resampling as postprocessing. And anyway it's really fast :)
> I have planned to do the following test:
> 1. Generate a set of random frequency/amplitude/phase triples below
> some frequency Fc.
> 2. Using sin() generators, one per above triples, output a float
> signal to file with (i) source and (ii) target frequencies.
> 3. Resample the file (i), and compare the resampling against the
> file (ii).
If you need some help doing that with glame, ask me.
> The test could be done separately for different frequency bands
> so that inaccuraties in high frequencies don't mix with the results
> got for low frequencies. Low frequencies could be tuned better.
Anything above the nyquist frequency of the new rate will drop out anyway.
> If you're more interested in effects, you could check Kurzweil 2500's
> Algorithms manuals from
> ftp://ftp.youngchang.com/pub/Kurzweil/Pro_Products/K2000-K2vx-K2500/
> K2500/Documentation/KDFXALGS.ZIP
>
> It at least gives the whole picture of what effects are needed in
> a good synth system. There are also user's manuals and reference manuals
> for Kurzweil synths.
Kewl, thanks. Anyway, I'm approaching the needed effects just from the
guitar player side right now :) Using distortion and flanger and freeverb3
you get a really fat sound.
Cheers, Alex
--Repartee is something we think of twenty-four hours too late. -- Mark Twain
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