[Vorbis-dev] Ambisonia proposal

[Richard Lee]

> Also, there has been some recent work on channel mappings for OggPCM (uncompressed PCM data in an Ogg container), which may be related:

Our proposal involves only Vorbis.  Uncompressed PCM Ambisonics is already well catered for.

> It is indeed related. We are proposing a different ambisonic channel scheme (not speaker mapping though) called N3D (different to the usual FuMa scheme). The N3D scheme has a number of 'future proof' advantages, including no extra header info required and support for Higher Orders (up to 6th and beyond). It is also believed that the N3D scheme is more compatible with Vorbis compression.

We are asking only for

- Mapping = 1 

- some help in adapting the present Vorbis Lossless Stereo Coupling to a multi-channel file with highly correlated channels.

- the Vorbis decoder to have a simple default stereo decode of an Ambi file for simple stereo players.

> Then, there's also the Ambisonics page at the Xiph Wiki[2], which I recommend interested parties to check.

[2] http://wiki.xiph.org/index.php/Ambisonics

Unfortunately, this page has a lot of obfuscating info, some of it mine copied (by Gregory Maxwell) from our discussions about a year ago when Monty confirmed that Mapping = 1 was reserved for Ambisonics.

I should get rid of the confusing stuff which is no longer applicable.  But I'm on a slow line and editing Wiki pages is both expensive and frustrating for me.

> that is what the spec draft proposes. but one channel mapping type is not enough for defining all combinations of horizontal and vertical orders above 3rd order. for example 9 channels can be interpreted as 2/2 or 4/0 (2nd order horizonal 2nd order vertical or 4th order horizontal without any vertical component).

Mr. Oli, if you are AKA Mr. Thuns, you will see from 

http://docs.google.com/Doc?id=df4dtw69_3626qqq6st

that we adopt the Thuns / Travis scheme that allows us to specify any number of channels up to and beyond 255 without ambiguity and without further mapping types or metadata.

We believe the scheme we propose will slot into Vorbis with little or no fuss and provide immediate and long term enhancements for surround sound.

An Ambisonic Decoder Library is also in preparation but this is optional.  It includes sophisticate stereo decoding facilities.

But a simple stereo player can just use the default stereo decode in the Vorbis decoder.

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