[Speex-dev] Regression in wideband encoding quality between b1 and rc1

Jean-Marc Valin jean-marc.valin at usherbrooke.ca
Tue Dec 15 17:27:07 PST 2009

On 15/12/09 10:37, Blaise Potard wrote:
> Having recently upgrading to speex rc1, It occurred to us that there
> seems to have been a regression in the quality of encoding since
> version beta1.

Just curious, did you identify where exactly the regression occurred?

> We are compressing some 22khz wave files in wb mode with maximum
> quality / complexity in VBR, and the result was really great with
> speex beta1. With rc1 (or beta3), there is a clear degradation for
> fricatives, which gives a very audible (and annoying) feeling of a
> muffled voice.

22 kHz is not supported. The encoder will give you a warning about that. 
You can use the resampler to down-sample to 16 Hz.

> This problem does not seem to affect CBR encoding, only VBR. It does
> not appear to affect 16k files as much either.

I think the VBR code has been tuned a bit. If the problem doesn't occur 
at 16 kHz, then I don't really care.

> P.S.: Is there any plan to make uwb mode really usable? At the moment,
> compressed 32k wave files sound worse than 16k in maximum quality.
> Would it be a lot of work to make the bitrate of the upper band to
> depend on the quality setting, instead of being hard-coded at 1.8kb?

The uwb mode sucks and there's no way to change that without breaking 
the bit-stream. I recommend using the wideband mode instead. If you 
really want more than wideband, use CELT instead.



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