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

[fons at kokkinizita.net]

On Fri, Jan 07, 2011 at 11:46:00AM +0100, Jörn Nettingsmeier wrote:

> if you do that, check out bruce wiggins' paper on optimizing for
> irregular layouts. but it's nowhere near a recipe, you'll have to do
> some hefty number crunching to arrive at anything useful.

Understatement of the day :-)

> >>azimuth = arctan (y/x)
> >>elevation = arctan (z/(sqrt(x^2 + y^2))
> >>r = sqrt (x^2 + y^2 + z^2)
> >thanks i will dubble check with fons answer :-)
> 
> to my great relief, it looks like they are congruent :)
> of course, when you implement it, you have to do something about the
> singularities at 90 and -90 degrees elevation.

Which is one reason why you need atan2() and not atan(). 
The second one is that the normal arctan function has
a range of only 180 degrees:  atan(y/x) == atan(-y/-x)

> the reason i'm so nit-pickish about all this is that every single
> audio professional i've met who has had prior exposure to ambisonics
> has heard at least one distinctly unconvincing demo, which makes
> live harder for all of us.

True. And those unconvincing demos are in almost all cases the result
of systems being set up by people who either don't understand what
they are doing, or are using information that is plain wrong or at
least of very dubious quality. There's a lot of that around in
particular on the web.

Ciao,

-- 
FA

There are three of them, and Alleline.