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

Blaise Potard bpotard at gmail.com
Wed Dec 16 03:12:19 PST 2009

Hello Jean-Marc, and thanks a lot for your quick answer!

2009/12/16 Jean-Marc Valin <jean-marc.valin at usherbrooke.ca>:
> 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?

No. To tell you the truth, I tried yesterday to access the git
repository to track the changes, but it seems to not be available at
the moment, and I did not try any further. It still seems to be
offline today, by the way.

>> 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.

Yes, I know it is not officially supported, but it used to work quite
well with beta 1 and sounded much better than 16000k

>> 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.

To be fair, there is a difference in quality also at 16k, but it is
much harder to notice; I guess if you are maniac enough to be annoyed
by it, you probably would not be using 16k to start with...

>> 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.

I gave it a quick try (thanks a lot for pointing it out, by the way!),
and it definitely appears to be a really good alternative. We will
most certainly switch to it in the future (but we will probably wait
until version 1 is out).

Thanks again, and keep up it the great work!

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