[Vorbis-dev] Ambisonics in Ogg Vorbis

[Gregory Maxwell]

On 4/21/07, Richard Lee <ricardo at justnet.com.au> wrote:
> Gregory Maxwell gmaxwell at gmail.com wrote
>
> >It would be nice if someone with a working ambisonic playback rig
> would give me some feedback on the decodes of coupled encodes. :)
>
> Has anyone done this; tried coupled encode / decoder of ambisonic signals?

I did. I posted files for people to test on real ambisonic rigs, but
no one replied.

http://myrandomnode.dyndns.org/ambi-test/

I would really appreciate feedback.

> I get the impression from this forum, including Monty's post, that no one has tried ANY coupling on a multi-channel file.  And only point and lossless are in present use for stereo.

I created a new mode which is a losslessly fully coupled mode based
off the Vorbis -q6 mode.  I'm not using mapping 1 so normal decoders
will happily spit out a 4 channel ogg.

> Monty said 8 phase & 4 phase coupling were once used in the dim & distant past (for stereo) but not anymore.  Does anyone know how much improvement in packing efficiency they give?
>
> After Monty's post, Lossy coupling on Ambi files is VERBOTTEN !

Gains for lossless packing were pretty high. Higher than for typical
stereo files.. at least on the ambisonic files I tested.