[Vorbis-dev] 5.1 surround channel coupling

[Martin Leese]

"Sebastian Olter" <qduaty at gmail.com> wrote:

> Martin:
> > you haven't applied the Furse-Malham
> > weightings.
> > ...
> > The Furse-Malham weightings were a recent
> > addition to the ".amb" specification (January 24,
> > 2007), so you may have missed it.
>
> Yes, I have definitely to clear my Firefox's cache;) I simply didn't
> think about normalization - especially in the context of a lossy
> codec. Anyway, an updated version of the function (and patch) is in
> attachment. Could you look at these equations again?

Looks good.

> I added 3rd order, just for curiosity. 16 channels exceed mplayer's
> limits, so a good [GPL'd] Ambisonic decoder library will be useful.
> Does anybody know (and better: support) such a library?

Don't know of such a library.

> AFAIK, the correct way to mix down B-Format into stereo is UHJ.

Yes, two-channel UHJ is stereo-compatible (and
mono).  Two-channel UHJ is produced from
first-order horizontal B-Format (W,X,Y) using
the following equations (where j is a +90 degree
phase shift):

S = 0.9396926*W + 0.1855740*X
D = j(-0.3420201*W + 0.5098604*X) + 0.6554516*Y
Left = (S + D)/2.0
Right = (S - D)/2.0

> Again:
> is there a library to do this?

Not as far as I know.

Regards,
Martin
-- 
Martin J Leese
E-mail: martin.leese at stanfordalumni.org
Web: http://members.tripod.com/martin_leese/