[LAU] ambisonics: fons ambdec and muse.demon.co.uk ambidec

[fons at kokkinizita.net]

On Fri, Jan 07, 2011 at 10:01:50AM +0100, Arnold Krille wrote:

> Ambisonic when shipped seems to be normalized to distance of 1 unit.
> When your speaker array is much bigger or smaller, one could use that 
> information to rescale the sound reproduction.
> But I haven't actually thought about this or even tried some formulas... Might 
> not work.

The real-valued gain factors used in an AMB panner normally correspond to
a plane wave, i.e. a source at infinite distance, not to some 'unit' 
distance. In NF-compensated encoding they correspond to some finite
distance (which has to be specified), but I haven't seen that used in
practice. 

> One other usage for the distance is for near-field compensation. I believe 
> fons' ambidec can do that, but isn't using the distance for this.

On the contrary, the distances are the only information ambdec has in
order to do near-field compensation. 

> Finally, one of the main advantages of ambisonics compared to that 5.1/7.1-
> crap is that your setup doesn't have to be perfect. Different distances and 
> even different irregularities in shape can be compensated and still reproduce 
> the signal as intended.

Up to some limits. It's absolutely not true that AMB will perform well
on arbitrary speaker layouts. It will try to make the best of it, but
the result may still below expectations.

Ciao,

-- 
FA

There are three of them, and Alleline.