[Flac-dev] (Universal) Ambisonic implementation
brianw at sounds.wa.com
Sun Oct 4 18:06:27 PDT 2009
On Oct 4, 2009, at 16:48, James Cloos wrote:
> I always thought that the best way to put ambisonic media in flac
> was to
> use an ogg container, with the 0-order w channel in one flac
> stream, the
> three first-order channels in a second flac stream, the five second-
> channels in a third flac stream and the seven third-order channels
> in a
> forth flac stream.
> An alternative would be to group the 0-order and first order into the
> first stream and continue as above for the second and third order
This was my first thought, but I did not know how well received the
idea would be.
> Keeping the same-level channels together should help the compression,
> but different-order channels are likely to have less inter-dependence.
Very true. I'm not sure how the three (?) first order channels would
allow FLAC to take advantage of inter-dependence, because I cannot
remember the limits of the current algorithm. Certainly, stereo is
analyzed, as are mid-side and a few other variations. I'm just not
sure whether any advantage is gained beyond two channels. Archives
of this list should have comments from Josh about the current
> Limiting each flac stream to just same-order channels requires four
> flac streams for a sixteen-channel third-order ambisonic, rather
> than just two streams, but makes it easier to drop the higher-order
> channels when desired.
> Allocation of forth and higher order ambison channels into the flac
> streams is left open, but higher orders are increasingly difficult
> to record and therfore are increasingly rare. Forth and higher level
> may be a purely theoretical concern.
This also makes sense.
Perhaps you should write up an official recommendation!
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