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

[Jean-Marc Valin]

> > The only potential problem is the one where two people are talking at
> > the same time. In this case, the solution could be to just boost the
> > bit-rate for a couple frames.
> 
> are you sure this will give us good results for both voiced and unvoiced sounds ?

I believe unvoiced sounds won't be a problem, but voiced sounds could
(especially two simultaneous vowels at different pitch and very
different LPC), but increasing bit-rate could still work.

> i'm asking because this could raise an alternative solution.
> assuming with have two speech signals, s1,s2. if Speex can encode
> s1+s2, it should be able to encode s1-s2, as well. right ?
> in this case, our "common" track could be the original english (s1)
> soundtrack encoded at ~100kbps vorbis, and the german track (s2) would
> be encoded as speex of s1-s2.

I don't think this would work. Encoding one track with occasional
double-talk would make sense (even if we need to triple bit-rate for the
few double-talk instances), but continuous double-talk would cause too
much problems.

Plus there's another, more important problem. Consider s1 (english
track) is encoded with Vorbis and s2-s1 is encoded with Speex. Unless
the compression is lossless, adding the two signals back won't remove
the english track completely (because the Speex and Vorbis won't have
the same "error signal").

> > > the first step is :
> > > - decide how we extract the 'common' track
> > 
> > I'll leave that one to you. I have no idea about the properties of the
> > different tracks.
> 
> ok. maybe anyone else in the list have ideas ?

Just a thought: ICA (Independent Component Analysis) might be able to do
it. Not sure whether it's good enough though. It has to do a perfect job
if you don't want to end up with the problem I described above. So I'm
not sure whether the project is feasible at all without access to the
"original" common track.

        Jean-Marc


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

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