Subject: Re: [ecasound] Resampling
From: Kai Vehmanen (k@eca.cx)
Date: Mon Apr 09 2001 - 08:46:22 EEST
On Mon, 26 Mar 2001, S. Massy wrote:
> I always used to think that resampling was more noisy when done with
> ecasound than with other apps and today I decided to just check to see
> whther I was right or not. So I both down and upsampled a file with
Yup, it's noisy. Ecasound uses simple linear interpolation, which is the
most straightforward (and _fastest_) way to resample. Resampling, if done
properly, is a complex and cpu-heavy task. Basicly you should not be
resampling while doing multichannel and/or realtime processing. If you
have files sampled at different sample rates, it's better to resample them
first (for instance with sox) to common sample rate, and then adjust
ecasound's internal sample-rate to that rate. Otherwise you'll be wasting
lots valuable cpu-power.
But although I'm not spending time on this myself, I won't object if
someone ports a better resampling algorithm to ecasound (for instance from
sox). ;) But I don't think this will be a runtime option. So you either
have 1) a compile time option for selecting a resampling algorithm, or 2)
a separate ecatools app (ecaconvert?) that can handle resampling better
than the main ecasound engine.
PS If you still want to use ecasound for resampling, you can for instance
add a lowpass filter (with a high Hz-value) to cut out the added
high-frequency noise. Many resampling algorithms do this by default.
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