[Vorbis-dev] Ambisonics in Ogg Vorbis

[Richard Lee]

Paul Martin wrote :

> 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.

This is a "cardioid" decode; fairly non-descript.  Used mainly for large area performance.  If your material is meant to be used at home, an "Energy" decoder is better and can be obtained by replacing +-0.1768 with +- 0.25 in the above script.

"SHELF FILTERS for Ambisonic Decoders" from

www.ambisonia.net\Members\ricardo

Gregory Maxwell wrote :

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

>From the nature of Ambisonic signals, I expect at least 2:1 gain if not more for lossless multichannel coupling of Ambisonic B-format.



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