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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, Meridean) 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.) Surround Sound Specifications For the following sections, a distinction is made between the number of discrete channels encoded in the original signal, and the number of channels that are reproduced for playback; these can be added using matrix decoding. A distinction is also made between the number of channels reproduced for playback, and the number of speakers over which these channels are played. Additionally, 5.1, 6.1, and 7.1 formats make use of bass management, which allows sound that is below the abilities of main channels (5.0 channels) to be redirected to the subwoofer, which is designed to handle that frequency range. There are notation differences between the pre-bass-managed signal and once it has passed through bass manager. For example, in 5.1, the channels are referred to as L(eft), R(ight), C(enter), L(ow )F(requency)E(effects), S(urround)L(eft), and S(urround)R(ight). However, once passing through the bass manager, they are referred to as L(eft), R(ight), C(enter), Sub(woofer), S(urround)L(eft), and S(urround)R(ight). 3.0 Surround (matrixed) Extracts 3 audio channels from a stereo source: 4.0 Surround (matrixed Quadraphonic) Extracts 4 audio channels from a stereo source: 4.1 Surround (matrixed Prologic) Extracts 4 audio channels from a stereo source: 5.1 Surround (matrixed Prologic II) Extracts 5 audio channels from a stereo source: 5.1 Surround (discrete Dolby Digital, DTS) Delivers six audio channels: 6.1 Surround (discrete Dolby Digital EX, DTS-ES) 6.1, which was developed by Gary Rydstrom and Anthony Grimani and is typically delivered as Dolby Digital EX or DTS-ES, adds a Surround back channel to the 5.1 setup. The additional surround back information is stored in the Dolby Digital EX format as a matrixed signal, meaning that audio that is in phase and equally in the Sl and Sr channels will be played in the Surround Back channel. DTS-ES allows for a discrete Surround back signal, but most programs are stored as a matrixed signal. Some 6.1 playback systems do use dual-mono Sb channels. 7.1 Surround (discrete SDDS) 7.1 adds two additional rear speakers to 5.1. Some computers and video game systems are capable of outputting a discrete 7.1 signal, and a number of mid-range and high-end receivers support 7.1, but often refer to playing a 6.1 signal over a 7.1 setup. This is usually accomplished by duplicating the surround channel (6th channel) to the additional 7th channel. In theory, this improves envelopment of sound where a big space exists between the rear surround speakers. The 7.1 system is also known as the SDDS system (Sony Dynamic Digital Sound), developed by Sony for large cinema halls. These incorporate Left Center (LC) and Right Center (RC) channels between the Left and Center channels and the Right and Center channels respectively. 8 Channel Audio Cinematic 8 channel audio is a commercial surround sound standard that adds two speakers to the more conventional, and consumer-oriented 6-channel (5.1) audio set-up. 8-channel positional audio utilizes the standard front, center, and LFE (bass) speaker configuration, but in addition, includes two speakers positioned by the side and two by the backside. Using such a sound configuration, almost every angle of sound can, theoretically, be captured for a completely immersive experience. But the 8-channel format has another, even more well-established tradition. The history of 'electronic music' includes the evolution of multi-channel playback in concert (arguably the real roots of 'surround sound' for cinema) and for a considerable time the 8-channel format was a de facto standard. This standardisation was fostered, in great measure, by the development of professional and semi-professional 8-track tape recorders - originally analog, but later manifesting in proprietary cassette formats by Alesis and Tascam. The speaker configuration, however, is much less traditional, and unlike cinematic reproduction systems, there is no hard-and-fast 'standard'. In fact, composers took (and to some extent still take) considerable interest in experimenting with speaker layouts. In these experiments, the goal is not limited to creating 'realistic' playback of believably natural sonic environments. Rather, the goals are frequently simply to experience and understand the effect created by variations on source and imaging. 10.2
Notation This notation, e.g. '5.1', reflects the number of full range, discrete channels; including a ".1" to reflect the limited range of the LFE channel. e.g. 5 full-range channels + 1 LFE channel = 5.1 It can also be expressed as the number of full-range channels in front of the listener, separated by a slash from the number of full-range channels beside or behind the listener, separated by a decimal point from the number of limited-range LFE channels. e.g. 3 front channels + 2 side channels + an LFE channel = 3/2.1 This notation can then be expanded to include the notation of Matrix Decoders. Dolby Digital EX, for example, has a sixth full-range channel incorporated into the two rear channels with a matrix. This would be expressed: 3 front channels + 2 rear channels + 3 channels reproduced in the rear in total + 1 LFE channel = 3/2:3.1 Note: The term stereo, although popularised in reference to two channel audio, can also be properly used to refer to surround sound. See also | |||||||||
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