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

[Jean-Marc Valin]

> these days we think about MultiLingual vorbis defenitions, and the best
> compression we could acheive were if we could save the common track on
> two channels, and then save the delta between the common track to the
> specifiec language (english speech/italian speech/etc'..) on a low
> bandwidth track. a vocoder track for this task could be very
> interesting. don't you think ?

Probably, what kind of bandwidth (sampling rate) and bit-rate are you
thinking about?

> another point,
> I wanted to ask why you had decided to develop CELP, which is based on
> linear prediction (LPC), while there are multi-band excitation (MBE)  
> speech coders (IMBE/AMBE) that have better compression-gain (down to 2kbps),
> and consumes less MIPS. i heard some samples of DVSI's vocoders, and i 
> must admit that their quality is very very good.
> LPC is abit old, isn't it ?-)

Well CELP (mostly CELP variants) is still the most widely used technique
for speech coding. If you look at the latest standards (like G.729 and
AMR wideband), most use ACELP (which we cannot use because of patents,
but that's another thing). Note that CELP has nothing to do with LPC
vocoders (aside from the fact that is uses LPC analysis). There are
other techniques, like WI (waveform interpolation) and sinusoidal coding
(not sure about MBE), but most of them are for low bit-rate coding (in
the 4 kbps range). Our current goals focus more on high quality that low
bit-rate.

That being said, the Speex is an open-source project and the code is
designed so that it's really easy to change any part of the codec (LSP
quantization, pitch, fixed codebooks, ...). So you can play with it if
you like and if you find something that works well, let us know.

        Jean-Marc

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

<p>--- >8 ----
List archives:  http://www.xiph.org/archives/
Ogg project homepage: http://www.xiph.org/ogg/
To unsubscribe from this list, send a message to 'vorbis-dev-request at xiph.org'
containing only the word 'unsubscribe' in the body.  No subject is needed.
Unsubscribe messages sent to the list will be ignored/filtered.