[Flac-dev] Code for Ambisonics

[Martin Leese]

On 3/22/07, Brian Willoughby <brianw at sounds.wa.com> wrote:
...
> But to return to your question, exactly what kind of "support" are
> you looking for?

I wasn't looking for any particular support, but
just to see what support was there (if any).

...
> I do not believe that there is any need for code specifically
> supporting Ambisonics.  FLAC supports conversion to and from other
> audio formats which hold multiple channels.  Ambisonics B-format
> involves channels WXYZ, C-format is UHJ or BHJ, G-Format can be any
> number of channels, but typically 5.1 on DVD.  You can work with
> Ambisonic recordings by either using individual mono files for each
> of the Ambisonic channels, or by using a 4-channel or 6-channel
> AIFF.  All of these files can be compressed into FLAC and expanded
> again without loss.

B-Format is not a set of speaker feeds, and
needs to be routed to a decoder in your living
room.  It would therefore be useful to have a
flag identifying the file as B-Format.  For example,
the ".amb" format (based on WAVE-EX) uses
unique GUIDs for this.

UHJ format is stereo compatible, but can also
be decoded back into surround sound.  Again,
a flag identifying the file as UHJ would be useful
to give a player the opportunity to do this.  The
".uhj" format (based on WAVE and WAVE-EX)
uses a chunk for this.

G-Format files can contain coefficients to allow
the B-Format channels to be recovered.  These
can then be decoded to a speaker layout
different from the one assumed when the
G-Format file was created.  This can only
happen if there is some way of identifying the
file as G-Format, and some way of incorporating
the coefficients into it.

In each case there is no need to change the
audio data, but in each case there is a need
for identifying flags.

Hope this helps.

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