Speex dev - Dec 2009 - Regression in wideband encoding quality between b1 and rc1

Hello,

To start with, thanks a lot for making such a great voice codec available!

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.

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.

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

Hope that will help you improve speex again!
Blaise

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?

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.

Cheers,

	Jean-Marc

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!
Blaise