Ambisonics

Ambisonics is a full-sphere surround sound technique: in addition to the horizontal plane, it covers sound sources above and below the listener.

Unlike other multichannel surround formats, its transmission channels do not carry speaker signals. Instead, they contain a speaker-independent representation of a sound field called B-format, which is then decoded to the listener's speaker setup. This extra step allows the producer to think in terms of source directions rather than loudspeaker positions, and offers the listener a considerable degree of flexibility as to the layout and number of speakers used for playback.

Ambisonics was developed in the UK in the 1970s under the auspices of the British National Research Development Corporation.

Despite its solid technical foundation and many advantages, Ambisonics has not been a commercial success, and survived only in niche applications and among recording enthusiasts.

With the easy availability of powerful digital signal processing (as opposed to the expensive and error-prone analog circuitry that had to be used during its early years) and the successful market introduction of home theatre surround sound systems since the 1990s, interest in Ambisonics among recording engineers, sound designers, composers, media companies, broadcasters and researchers has returned and continues to increase.

Ambisonics can be understood as a three-dimensional extension of M/S (mid/side) stereo, adding additional difference channels for height and depth. The resulting signal set is called B-format. Its component channels are labelled ${\displaystyle W}$ for the sound pressure (the M in M/S), ${\displaystyle X}$ for the front-minus-back sound pressure gradient, ${\displaystyle Y}$ for left-minus-right (the S in M/S) and ${\displaystyle Z}$ for up-minus-down.

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