[opus] ambisonics formats and channel mappings

Martin Leese martin.leese at stanfordalumni.org
Wed Jun 1 18:11:14 UTC 2016

Michael Graczyk wrote:
> UHJ is an interesting way to preserve compatibility with non-ambisonic
> playback systems.
> If UHJ becomes popular in the future, we could
> specify rules for encapsulating UHJ in Ogg.

I guess it depends on how you define popular.
The UHJ Discography lists over 270
UHJ-encoded records.  This EXcludes over
450 releases by Nimbus Records.  The UHJ
Discography is available at:

> I believe that [UHJ] should use
> a different channel mapping for simplicity.

This looks sensible.  Marc and Sampo have
described how UHJ is limited to first order,
and has 2-, 3-, and 4-channel variations.  (I
suggest we drop the "2.5" channel as it was
only for use in radio broadcasting and
required unwelcome compromises in the
decoder design.)

Note that a mechanism is required to prevent
systems that do not recognize the UHJ
channel mapping from interpreting 4-channel
UHJ as 4-channel quad and downmixing to
stereo.  Instead, the first two channels should
be played in stereo and the last two channels
ignored.  OggPCM has such a mechanism.

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

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