fons at kokkinizita.net fons at kokkinizita.net
Wed Feb 24 14:29:46 UTC 2010

```On Wed, Feb 24, 2010 at 05:01:20PM +0300, alex stone wrote:
> Jorn, Fons,
>
> I'm getting deeper into a setup now, and trialling a few different configs.
>
> A further question.
>
> Given that an amb sphere is equal on all "sides", and the sweet spot
> is the centre (roughly speaking), should i be configuring my dry sound
> orchestral instruments/sections to use the upper-rear/rear quadrant of
> the sphere, assuming the centre is the listener, in a total space? In
> a real world setup, my orchestra is on the stage, and the listener may
> well be (at my choice) sitting in a spot equidistant from the
> back/front/left/right of the total space. Should i assume this as a
> point of reference to begin with?

I get a bit confused. Usually 'the stage' is considered to be
'front', the positive X direction. You can decide otherwise
when mixing Ambisonics, but in a normal concert hall the
orchestra would be in the front direction. Upper-rear would
be a balcony area, or just some walls.

> My "speakers" will be not only on stage, but as ambient
> sound/reflections in the rest of the space as well. The
> space isn't exactly spherical.

Don't think in terms of a 'spherical space'. Ambisonics as
we use it here does not consider distance. Every point on
the sphere just corresponds to a direction as seen from
the center. It's just a mathematical abstraction, the set of
directions in 3-D space is equivalent to the set of points
on a sphere.

Distance and the shape of the space are encoded in the
time patterns of direct sound and early reflections.

earlier maybe this can be explained as follows.
An Ambisionic (B-format) signal, no matter how it was
generated, can be considered as the output of a B-format
microphone placed at a specific place in some sound field.
You can use the B-format signals to compute the output
that any normal mic would produce when placed in the same
spot. Using two of such 'virtual microphones' pointing in
different directions produces a stereo signal. It is the
classic way to obtain a stereo version of an Ambisonic
recording or mix. One of the plugins in the AMB set will
do this.

Ciao,

--
FA

O tu, che porte, correndo si ?
E guerra e morte !

```