[vorbis-dev] Channel coupling in Vorbis

[Thomas Marshall Eubanks]

Ralph Giles wrote:

> On Mon, 14 Aug 2000, Jean-Marc Valin wrote:
>
> > I saw from the interview on Slashdot that there is no support for channel
> > coupling in Vorbis. I would like to help work on that. Has anything been started
> > about that? I don't know yet whether if could work "in real life", but I have
> > started to work on a way to do adaptative coupling between two channels (by
> > finding the best transformation to predict one channel from the other).
>
> As I understand it, the plan is to implement joint stereo and surround at
> the same time, based on ambisonic encoding. You should check the list
> archives, but there hasn't been much discussion; I've no idea what Monty
> intends as far as compression of the channels.
>
> David Carter's original proposal is at:
>
> http://www.xiph.org/archives/vorbis-dev/0844.html
>
> And there's some good background at the ambisonics website:
>
> http://ambisonic.net/
>
> > I would like to know whether I can be useful. I have some experience in audio
> > processing/coding (mostly speech).
>
> Hope that helps,
>  -ralph
>
> --
> giles at ashlu.bc.ca
>
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I would recommend NOT using the ambisonic for surround sound. I read the specs on this - it
uses a spherical harmonic expansion of the sound field. The trouble with that is
that it is 3-D. Unless you plan to have speakers in your ceiling, it will waste 1/3 of
your bandwidth and (except for the dipole terms) won't separate cleanly into
high and low bitrate channels (or horizontal versus vertical). Also, I believe that
ambisonic is "color blind", while clearly the separation of the monopole and other
terms is best NOT done on a  frequency independent basis.

                                 Regards
                                 Marshall Eubanks

T.M. Eubanks
Multicast Technologies, Inc
10301 Democracy Lane, Suite 410
Fairfax, Virginia 22030
Phone : 703-293-9624
Fax     : 703-293-9609
e-mail : tme at on-the-i.com     tme at multicasttech.com

http://www.on-the-i.com http://www.buzzwaves.com

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