Re: [sc-users] 2nd order ambisonics in 2D setup

[Christopher Frauenberger <frauenberger@xxxxxx>]

Hi,

If you use only 2D with 3D encoder/decoder matrices all channels  
regarding the z axis would automatically zero out (i.e. all channels  
containing a sin(elevation) term). For Ambisonics 3rd order this  
means channel 4, 7,8,9, 12, 13 and 16.

simply try:

p = ProxySpace.push;
~test = { EnvGen.kr(Env.adsr, Impulse.kr(3)) * PinkNoise.ar(0.8); };
~elev = {|e=0| e};
~enc = { PanAmbi3O.ar(~test.ar, MouseX.kr(-pi, pi), ~elev.kr) };
~dec = { DecodeAmbi3O.ar(~enc.ar, '1_4_7_4') };

~enc.scope

and you would see these channels be silent.

For decoding this means, that only the speakers on earlevel (in the  
default 1-4-7-4 setting the ring of 7) would receive signals.

~dec.scope;

The minimum number of speakers you would need for 2D Ambisonics is  
therefore (2m +1), m being the order while as for 3D it is (m+1)^2.

A good basic introduction is Bamford's thesis on 1st and 2nd order  
Ambisonics:
http://audiolab.uwaterloo.ca/~jeffb/thesis/thesis.html

More information on binaural Ambisonics
http://iem.at/Members/noisternig/bin_ambi/
http://iem.at/projekte/publications/paper/binaural/view

hope it helps
Chris



On 13 May 2006, at 17:57, Sciss wrote:

> hallo,
>
> i wonder how many channels one would need to transport an encoded  
> 2nd order ambisonic signal, when the decoding setup is strictly  
> 2D ... i know for 3D the channel num is (M + 1)^2 where M =  
> ambisonics order, so 1st order is four channels W X Y Z, 2nd order  
> is nine channels. but looking at DecodeB2 you can throw away the Z  
> channel if decoding only two-dimensional speaker setups. so can i  
> through away a couple of channels when using 2nd order with two- 
> dimensional speaker setup? if i use IEM's PanAmbi2O, which channels  
> would that be, and can i use DecodeAmbi2O with dummy signals  
> (probably silent?) for the discarded channels?
>
> thanks, -sciss-
>
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