[Vorbis-dev] Ambisonics in Ogg Vorbis

[Paul Martin]

On Sat, Apr 21, 2007 at 03:36:16AM -0400, Gregory Maxwell wrote:
> 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.

If you haven't got a true Ambisonic setup, you can get a flavour by
using the following script to convert a 4 channel .amb to a 4 channel
"square" speaker arrangement. (The latest SoX has a bug in the mixer
function, which stops it taking 16 numbers.)

sox -V -S $1 -c 4 -3 -r 48000 $2 \
 mixer \
 0.3536,0.3536,0.3536,0.3536,\
 0.1768,0.1768,-0.1768,-0.1768,\
 0.1768,-0.1768,-0.1768,0.1768,\
 0,0,0,0 \
 rabbit stat

This then gives you a file with the channels in the format Left
Front, Right Front, Left Rear, Right Rear.

You can then use ffmpeg or aften to turn it into AC3/A52 if you don't
have discrete channel output.

(Coefficient matrix from
http://www.muse.demon.co.uk/ref/speakers.html)


-- 
Paul Martin <pm at zetnet.net> (work)
  <pm at nowster.zetnet.co.uk> (home)