Ambisonics (not to be confused with ambio-
phonics) is a series of recording and replay
techniques using multichannel mixing tech-
nology that can be used live or in the studio.
By encoding and decoding sound information
on a number of channels, a 2-dimensional
("planar", or horizontal-only) or 3-dimension-
al ("periphonic", or full-sphere) sound field
can be presented. Ambisonics was invented
by Michael Gerzon of the Mathematical Insti-
tute, Oxford, who – with Professor Peter Fell-
gett of the University of Reading, David
Brown, John Wright and John Hayes of the
now defunct IMF Electronics, and building on
the work of other researchers – developed
the theoretical and practical aspects of the
system in the early 1970s.
Ambisonics offers a number of advantages
over other surround sound systems:
• It is isotropic in that sounds arriving from
all directions are treated equally (as
opposed to most other surround systems
that assume that the main sources of
sound are frontal and that rear channels
are only for ambience or special effects).
• All speakers are generally used to localise
a sound in any direction (as opposed to
conventional pan-potted (pair-wise mixing)
techniques which use only two adjacent
speakers). This gives better localisation,
particularly to the sides and rear.
• The stability and imaging of the
reproduced soundfield vary less with
listener position than with most other
surround systems. The soundfield can
even be appreciated by listeners outside
the speaker array.
• A minimum of four channels of
information are required for distribution
and storage of a full-sphere soundfield,
and three for a horizontal soundfield. (This
is fewer than other surround systems).
Full-sphere replay requires a minimum of
six loudspeakers (a minimum of four for
horizontal), the signal for each speaker
position being derived using appropriate
circuitry or software.
• The loudspeakers do not have to be
positioned in a rigid setting; most regular
polygons and (with somewhat more