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