Ambisonics is a technique for encoding sound information on a number of channels to reproduce a "3 dimensional" sound field. The sound information is encoded into 4 channels: W, X, Y and Z. This is called the Ambisonics B-format. The W channel is the general loudness of the signal. The X, Y and Z channels are the directional components in three dimensions. The loudspeaker signals are derived by using a linear combination of these four channels and is dependent on the actual position of the speaker in relation to the center of an imaginary sphere going through all available speakers.
For the general two dimensional case (no height information) and placing the loudspeakers on a circle, we can derive the loudspeaker signals from the using W, X and Y channels:
Proponents of this technique assert that is a superior form of surround sound for a number of reasons:
- it allows better localization of sound outside of the sweet spot
- it only requires 4 speakers to generate a horizontal sound field (full surround requires 5 and 1 special effects speaker)
- it only requires 6 speakers to generate a full 3D sound field.
- only 4 channels of information are required for transmission and storage, though replay can be by more than 4 loudspeakers as it is possible to derive a signal for each speaker position using appropriate circuitry.
- the loudspeakers do not have to be positioned in a rigid setting.
The Ogg Vorbis project has shown interest in implementing ambisonics as a means for including surround sound in their project.
Research is ongoing, particularly into "higher-order" systems that provide even more detailed localisation.
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