Surround sound is the concept of expanding the spatial imaging of audio playback from one dimension (mono/Left-Right) to two or three dimensions.
This is often performed for a more realistic audio environment, actively implemented in cinema sound systems, technical theatre, home entertainment, video arcades, computer gaming, and a growing number of other applications.
Many popular surround sound formats have evolved over the years. They include discrete 5.1 Surround sound on DVD-Audio (DVD-A) or SACD (Super Audio CD), Ambisonics, quadraphonic, Dolby 5.1 Surround sound, DTS, DVD-Video (DVD-V), and MP3 Surround.
Surround sound can be created using several methods. The simplest to understand uses several speakers around the listener to play audio coming from different directions. Another approach involves processing the audio using psychoacoustic sound localization methods to simulate a 3D sound field using headphones. The third approach, which is based on Huygens’ principle, attempts to reconstruct the recorded soundfield wavefronts within the listening space and so might be regarded as a form of “audio hologram”. There are two related forms of this approach, the first of which, Ambisonics, provides an exact reconstruction at a central point and a less and less accurate reconstruction as you move away from this point. The second form, wave field synthesis or WFS, produces a soundfield which, whilst not absolutely accurate anywhere, has an even error field over the whole area. WFS (of which two commercial systems are available, one from the Swiss company sonic emotion and one from Iosono) requires a large number of loudspeakers and a considerable amount of computing power to produce its results whereas Ambisonics, for which there is a significant amount of both free and commercial software available (as well as some hardware from, for instance, Meridian Audio, Ltd.) requires far fewer resources, at least in its simplest form (this is no longer so true for more recent developments such as Near Field Compensated Higher Order Ambisonics). In the limit, WFS and Ambisonics converge as was shown some years ago by Rozzenn Nicol and Marc Emerit but for the present Ambisonics has a far greater market penetration in the domestic arena and especially amongst musicians involved in electronic and computer music. Some consumer electronic devices (AV receivers, stereos, and computer soundcards) have digital signal processors or digital audio processors features built into them to simulate surround sound from stereo sources.
Though generally the province of big-budget movie productions and sophisticated video games, some consumer camcorders (particularly DVD-R based models from Sony) have surround sound capability either built-in or available as an add-on. Though considered by camcorder reviewers to be of dubious utility, it is nevertheless one of the few ways that someone not using professional equipment can create surround sound. (The MiniDV spec does allow up to four channels of sound, making it theoretically possible for such camcorders, but it is seldom implemented that way.)
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