Description
This article is from the Ambisonic
Surround Sound FAQ, by Martin Leese with numerous
contributions by others.
5. What are W, X, Y and Z?
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.
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