Encode a two channel signal to two dimensional ambisonic B-format. This puts two channels at opposite poles of a 2D ambisonic field. This is one way to map a stereo sound onto a soundfield. It is equivalent to:
Input signal A
Input signal B.
Position around the circle from -1 to +1.
-1 is behind, -0.5 is left, 0 is forward, +0.5 is right, +1 is behind.