[vorbis-dev] Re: Speex: Open-source, patent-free speech coding

[Jean-Marc Valin]

> sampling-rate should be high (48khz), but bandwidth should be less than 
> 16khz (after "extracting" speech-only from the lingual track).

Currently, Speex only supports sampling at 8 kHz and 16 kHz, so it would
need to be adapted to work at 32 kHz (and then up-sample to 48 kHz). I'd
say it's quite feasible.

> about bitrate, let me describe something :
> up until vorbis came, people used to encode their soundtrack of movies 
> at 128kbps to 192kbps MP3. now, with Ogg, we can encode the "common"
> track at around 100kbps vorbis, and encode each speech track at less
> than 30kbps with speex. this gives us about 180kbps for a movie with
> three soundtracks (english/italian/francis, for instance).
> that could make a small revolution :).

I think 30 kbps is realistic. When we add VBR, the average could easily
drop to ~16 kbps/track.

> you can find some info about MBE over at :
> http://www.dvsinc.com/papers/mbe.htm

This info seems very biased to me...

So I'd say the first step would be to build a prototype that downsamples
the 48 kHz stream to 16 kHz and encodes it with the current Speex
version. Once that works, we can try making Speex work at 32/48 kHz.
Actually, that *might* not even be necessary, as most of the energy in
speech is in the 0-8 kHz band - and even the 4-8 kHz band can in some
cases (speech only) be severely distorted before the ear can tell the
difference.

        Jean-Marc


-- 
Jean-Marc Valin, M.Sc.A.
LABORIUS (http://www.gel.usherb.ca/laborius)
Université de Sherbrooke, Québec, Canada

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