Last-modified: 21 January 1998
Copyright: © 1994, 1995, 1996, 1998 by Martin J Leese
Distribution is unlimited
With Ambisonic technology, the directionality of the sound field is composed of spherical harmonic components. The zero-order component is termed W and is omnidirectional. The first-order components are figure-of-eight (lemniscate) responses which point forward, left and up. These are termed X, Y and Z, respectively. In practice, second-order and higher components are ignored.
The W, X, Y and Z channels are collectively called B-Format.
The fact that the Z component can be recorded creates the opportunity for periphonic (full-sphere) reproduction. Periphony requires speakers to be placed above and below the height of the listeners' ears.
Readers familiar with microphone techniques will realise that the W and Y spherical harmonic components are equivalent to the M and S components of the M-S stereo recording technique. Ambisonics is a natural extension of this recording technique to three dimensions.