[Vorbis-dev] 5.1 surround channel coupling

[Ralph Giles]

Yes, we absolutely, really, really need 5.1 (etc.) modes for the vorbis 
encoder! This is really important for pushing free formats, especially
in the video realm.

There are a number of low hanging fruit, as have been suggested, 
including treating things as stereo pairs, doing a separate mode
that takes into account the low pass for the LFE channel(s), and
extending the square-polar mapping to >2 channels. There's probably
at least a factor of two in bitrate to be gotten here.

The step after that is to do a special tuned mode set for 5.1,
taking into account the mixing strategies used in practice. This
is much harder, requiring a golden ear and some working knowlege
from the industry. Monty has also cited the lack of (not lossily 
compressed) 5.1 sources to test with as an obstacle here.

The second step is what's needed to get quality/bitrate up to the 
same standards we offer for stereo, but that shouldn't stop anyone 
from working on the first step. For that all you need is a listening
setup and a willingness to experiment with the code.

I expect reasonable initial progress can be made with transcoded AC3 
tracks from DVD-Video discs. As far as lossless masters, we have the 
CC Elephant's Dream sound track, and a (not distributable) 5.0 classical 
music SACD master so far. If you have a master you're willing to let us 
tune against, please let me know.

FWIW,
 -r