Anyone who would like an introduction to spherical harmonics
expansions could have a look at this(which I wrote myself)
http://www.regonaudio.com/SphericalHarmonics.pdf
as an introduction for audio people.
It is perhaps worth noting that spherical harmonics
(and Fourier expansion of periodic functions)
are both special cases of expansion in eigenfunctions
of the Laplacian on a Riemannian manifold, a Riemannian
manifold being a generalization of the idea of a surface.
(I do this stuff for a living--excuse my wandering off
into generality).
But the article linked to is very down to earth!
Robert
On Sun, 23 Jan 2011, Eero Aro wrote:
Gus
As Fons already said, there is information available about Ambisonics.
First check out these two sites:
http://martin_leese.tripod.com/Ambisonic/
http://www.ambisonic.net/
In quadrophic systems the angle between adjacent speakers is
90 degrees (or more), which isn't enough to create stabile phantom
images between the loudspeakers. The angle should be 60 degrees
or less, especially at the sides of the listener. With quad the sound
image collapses, if you move or turn your head.
If you are not delivering discrete audio channels to the home listener,
you need some kind of decoding anyway, such as Dolby Digital, DTS, etc.
Augustine Leudar wrote:
Why cant you
do the same for 3 dimensianal sounds ? Four mics surround sending discrete
channels to four spekers placed in a square and one for height information
going to a mic above your head - this should naturally represent the sound
field without any decoding , Ive done this and it has been quite effective
You can. I believe that _effective_ is the correct word to describe that.
With 1st order Ambisonics, you can capture (or create by mixing) a three
dimensional soundfield by using four audio channels, the B-Format.
B-Format is a part of a hierarchical system, which you can use for
whatever playback you like, mono, stereo, horizontal surround or periphonic
(3D) surround.
Manipulating the three or four-channel signal is very easy and there's a lot
of things you can do with it. If you use a multitude of signals for your
3D-sound,
manipulating them needs a lot of processing power and tools that don't
exist. There are tools for the B-Format.
Using B-Format as a delivery format makes it possible, that the listener can
place his speakers as he wishes. The speaker layout is defined in the
decoder.
The number of speakers isn't restricted to any certain number. With
horizontal
surround you should have at least four speakers, with 3D six speakers.
It is possible to pre-decode an Ambisonic recording into a certain speaker
layout. You find info about the "G-Format" in Richard Elen's article "Getting
Ambisonics Around". It's in http://www.ambisonic.net/ under "Articles".
With G-Format you gain the possibilities of Ambisonic recording, mixing
and manipulating. What you lose, is the flexibility for the placing of the
loudspeakers.
In my opinion, you can skip the on-going discussion about UHJ, it's more or
less academic. UHJ was developed in the 1980's, at the time when vinyl LP
and FM radio were the most important carriers. UHJ isn't needed anymore.
But - you still need a decoder to decode the B-Format signals for the
loudspeakers.
Eero Aro
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