• Czech: obklopit
• Finnish: ympäröidä
• Japanese: 囲む, 取り巻く
• Portuguese: contornar
• Russian: окружать (okružát’) , окружить (okružít’)

• Czech: obklíčit
• Finnish: saartaa, piirittää
• Japanese: 囲む, 包囲する
• Portuguese: cercar
• Russian: окружать (okružát’) , окружить (okružít’)

• ttbc Arabic:
• ttbc Catalan: rodejar
• ttbc Chinese: 包圍, 包围 (bāowéi)
• ttbc Dutch: omringen
• ttbc French: entourer
• ttbc German: umringen
• ttbc Italian: circondare
• ttbc Korean: 둘러싸다 (dulleossada)
• ttbc Kurdish:
• ttbc Old English: bebūgan
• ttbc Spanish: rodear, cercar
• ttbc Swedish: omringa

Noun

surround

1. In the context of "UK": : Anything, such as a fence or border that surrounds something.

Derived terms

• surround sound

Multichannel audio is the name for a variety of techniques for expanding and enriching the sound of audio playback by recording additional sound channels that can be reproduced on additional speakers. Surround sound refers to the application of multichannel audio to channels encircling the audience (generally some combination of left surround, right surround, and back surround) as opposed to "screen channels" (center, [front] left, and [front] right), i.e. around 360° in the horizontal plane (2D). The sphere (3D) of human hearing perception can be approached by adding channels above and below the listener.

One of the first documented uses of surround sound was implemented in 1940 for Disney's classic animation, Fantasia. Dubbed 'Fantasound' it consisted of three audio channels which were diffused (panned—initially live by an engineer) around the cinema over up to 54 speakers, which was achieved through the use of the sum and the difference of the phase of sound.

Surround sound technology is used in both cinema and "home theater" systems, games consoles and PCs and a growing number of other applications.

Consumer surround sound formats include sound on videocassettes, Video DVDs, and HDTV broadcasts encoded as Dolby Pro Logic, Dolby Digital, or DTS. Other formats include the competing DVD-Audio (DVD-A) and Super Audio CD (SACD) formats; and MP3 Surround.

Theatrical film 5.1 surround formats include Dolby Digital, DTS, and Sony Dynamic Digital Sound (SDDS).

Surround sound hardware is mostly used by movie productions and sophisticated video games. However, some consumer camcorders have surround sound capability either built-in or available as an add-on. Some consumer electronic devices (AV receivers, stereos, and computer soundcards) have digital signal processors or digital audio processors built into them to simulate surround sound from stereo sources.

Creating surround sound

Surround sound can be created using several methods. The simplest method involves using one of many surround sound recording microphone techniques and/or mixing in surround for playback on an audio system which uses several speakers placed around the listener to play audio coming from different directions. A second approach is to process the audio using psychoacoustic sound localization methods to simulate a 2-D sound field using headphones.

A third approach, 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". One form, wave field synthesis (WFS), produces a soundfield which has an even error field over the whole area. WFS commercial systems made by the Swiss company sonic emotion and by Iosono, require a large number of loudspeakers and a considerable amount of computing power to produce their results.

Ambisonics is another form based on Huygens' principle. Ambisonics provides an exact reconstruction at a central point, and a less accurate reconstruction as you move away from this point. There is a significant amount of both free and commercial software available for Ambisonics, and Ambisonics has significant penetration in the consumer market, especially with musicians who use electronic and computer music. In addition, Ambisonics is standard in hardware surround products offered by Meridian Audio, Ltd. In its simplest form, Ambisonics consumes few resources. However, this is no longer true for more recent developments such as Near Field Compensated Higher Order Ambisonics. Some years ago it was shown that, in the limit, WFS and Ambisonics converge.

Surround sound can also be derived at the mastering level, from stereo sources as with Penteo, which uses FFT analysis of a stereo recording to break individual sounds apart into their component panorama positions, and then positions them accordingly into a 5-channel field.

Mapping channels to speakers

In most cases, surround sound systems have relied on the mapping of each source channel to its own loudspeaker. Matrix systems recover the number and content of the source channels and apply them to their respective loudspeakers. With discrete surround, the transmission medium allows for (at least) the same number of channels that the source and destination utilize.

However, one-to-one channel to speaker mapping is not the only way of transmitting surround information. The transmitted signal may encode the information defining the original soundfield to a greater or lesser extent; this is rendered at the replay end by a decoder which generates the number of loudspeaker feeds required to suit the number of speakers available for replay and their configuration. This "replay device independent" encoding is analogous to the process of encoding and decoding an Adobe PostScript file, where the file describes the page and is rendered according to the resolution of the output device. Audio rendering is used in Ambisonics and WFS systems. Meridian Lossless Packing contains elements of this capability.

Bass management

Surround replay systems may make use of bass management, the fundamental principle of which is that bass content in the incoming signal, irrespective of channel, should be directed only to loudspeakers capable of handling it, whether the latter are the main system loudspeakers or one or more special low-frequency speakers called subwoofers.

There is a notation difference before and after the bass management system. Before the bass management system there is a Low Frequency Effects (LFE) channel. After the bass management system there is a subwoofer signal. A common misunderstanding is the belief that the LFE channel is the "subwoofer channel". The bass management system may direct bass to one or more subwoofers (if present) from any channel, not just from the LFE channel. Also, if there is no subwoofer speaker present then the bass management system can direct the LFE channel to one or more of the main speakers.

Low Frequency Effects (LFE) channel

The Low Frequency Effects channel, or LFE, is a source of some confusion in surround sound. The LFE channel was originally developed to carry extremely low "sub-bass" cinematic sound effects (e.g., the loud rumble of thunder or explosions) on their own channel. When loud sub-bass effects are on a different channel, this allows theaters to control the volume of the sub-bass effects, so that it suits the size of their sound reproduction system and the acoustic environment of their cinema. Independent control of the sub-bass effects also reduced the problem of intermodulation distortion in analog movie sound reproduction.

In the original movie theater implementation, the LFE was a separate channel fed to one or more subwoofers. However, home replay systems may not have a separate bass speaker (subwoofer) that is able to handle the sub-bass effects. As a result, modern home surround decoders and systems often include a bass management system that allows bass on any channel (main or LFE) to be fed only to the loudspeakers that can handle low-frequency signals. The salient point here is that the LFE channel is not the "subwoofer channel"; there may not even be a subwoofer, and if there is it may be handling a good deal more than effects.

Some record labels such as Telarc and Chesky have argued that LFE channels are not needed in a modern digital multichannel entertainment system. They argue that all available channels have a full frequency range and, as such, there is no need for an LFE in surround music production, because all the frequencies are available in all the main channels. These labels sometimes use the LFE channel to carry a height channel, underlining its redundancy for its original purpose.

LFE is sometimes expanded as Low-frequency Enhancment.

Surround sound specifications

The descriptions of surround sound specifications below distinguish between the number of discrete channels encoded in the original signal and the number of channels reproduced for playback. The number of channels reproduced for playback can be changed by using matrix decoding. A distinction is also made between the number of channels reproduced for playback and the number of speakers used to reproduce (each channel may refer to a group of speakers). The graphics to the right of each specification description represent the number of channels, not the number of speakers.

3.0 Channel Surround (analog matrixed: Dolby Surround)

Extracts four audio channels from a specially encoded two-channel source:

• Two channels for speakers at the front—left (L) and right (R).
• One channel for speaker at the center—center (C).
• One channel for both surround speakers at the rear—mono surround channel (S).
• Describes the Dolby Pro Logic matrixed surround system. Source media, usually VHS, Laser Disc, television broadcast or CableTV/Satellite is often branded with "Dolby Surround" logo. This is the encoding used on the analog optical track for theatrical motion picture films.

Placement: (Five speakers in total) The front speakers should be placed at the edges of the screen, toed in to face the central listening location, and the tweeters should be ear height. The center speaker should be placed behind the screen (when using projection) or over or under a TV, and as close to ear-high as possible. Surround channel speakers should be placed at ear height, slightly behind the listening position, and should be of bi-pole construction.

5.1 Channel Surround (3-2 Stereo)(analog matrixed: Dolby Pro Logic II)

Extracts Five audio channels from either a specially encoded two-channel or a stereo source:

• Two channels for speakers at the front—left (L) and right (R).
• One channel for speaker at the center—center (C).
• Two channels for surround speakers at the rear—surround left (LS) and surround right (RS).
• One low-frequency effects channel (LFE).
• Describes the Dolby Pro Logic II matrixed surround system. Source media is often gaming systems including Playstation 2, GameCube and Wii games branded with "Pro Logic II" logo.

5.1 surround sound may also be referred to as 3-2 stereo. This defines the configuration that has been standardised for numerous surround sound applications. The term 3-2 refers to 3 front speakers and 2 rear speakers.

Placement: 5.1 speaker layouts should conform to the ITU-R BS.775 standard, despite the myth that music and video content require different placements. The ITU standard states that the left and right speakers are located at ±30˚, while the rear speakers should be positioned approximately ±110˚. There is speculation that rear loudspeakers at ±150˚ provide "more exciting surround effects".

5.1 Channel Surround (70 mm 6-Track) (analog magnetic)

Delivers six audio channels from a 6 channel source:

• Four channels for speakers at the front-left (L), left center (LC), right center (RC), and right (R).
• One channel for speaker at the center-center (C)
• One channel for surround speaker at the rear-monaural surround (S).

5.1 Channel Surround (3-2 Stereo) (analog magnetic: Dolby Stereo "Baby Boom")

Delivers five audio channels and 1 LFE channel from a 6 channel source:

• Two channels for speakers at the front—left (L) and right (R).
• One channel for speaker at the center—center (C).
• Two channels for surround speakers at the rear—surround left (LS) and surround right (RS).
• One low-frequency effects channel (LFE).

5.1 Channel Surround (3-2 Stereo)(digital discrete: Dolby Digital, DTS, SDDS)

Delivers five audio channels, one extracted audio channel and one LFE channel from a six channel source:

• Two discrete channels for speakers at the front—left (L) and right (R).
• One discrete channel for speaker at the center—center (C).
• Two channels for surround speakers at the sides—left surround (LS) and right surround (RS). The discrete LS and RS channels are dematrixed into LS, RS, and back surround (BS).
• One channel for surround speakers at the rear—back surround channel (BS).
• One low-frequency effects channel (LFE).
• Describes the Dolby Digital EX discrete/matrixed hybrid Surround system. Source media, usually DVD is often branded with "Dolby Digital EX" logo. This format is used in some theatrical motion picture films.

Placement: The front speakers should be placed at the edges of the screen, toed in to face the central listening location. The center speaker should be placed behind the screen (when using projection) or over or under a TV. Side channel speakers should be placed to the left and right of the listening position, equidistant from the front speakers and the rear speakers. Rear channel speakers should be placed slightly behind the listening position, and should have a normal high-quality monopolar construction. All speakers should be at ear height.

6.1 Channel Surround (digital discrete: DTS-ES)

Delivers six discrete audio channels and 1 LFE channel from a seven channel source:

• Two channels for speakers at the front—left (L) and right (R).
• One channel for speaker at the center—center (C).
• Two channels for surround speakers at the sides—side left (LS) and side right (RS).
• One channel for surround speakers at the rear—back surround channel (BS).
• One low-frequency effects channel (LFE).
• Describes the DTS ES discrete Surround system. Source media, usually DVD is often branded with "DTS ES" logo. In theatrical motion picture film, this format does not exist, and the name "DTS-ES" refers to the above hybrid format used for Dolby Digital EX.

Placement: The front speakers should be placed at the edges of the screen, toed in to face the central listening location. The center speaker should be placed behind the screen (when using projection) or over or under a TV. Side channel speakers should be placed to the left and right of the listening position, equidistant from the front speakers and the rear speakers. Rear channel speakers should be placed slightly behind the listening position, and should have a normal high-quality monopolar construction. All speakers should be at ear height.

7.1 Channel Surround (digital discrete: Dolby Digital Plus, DTS-HD, Dolby TrueHD)

Delivers seven audio channels and one LFE channel from an 8 channel source:

• Two channels for speakers at the front—left (L) and right (R).
• One channel for speaker at the center—center (C).
• Two channels for surround speakers at the sides—left surround (LS) and right surround (RS).
• Two channels for surround speakers at the rear—left back (LB) and right back (RB).
• One low-frequency effects channel (LFE).
• Describes the Dolby Digital Plus discrete Surround system. Source media, usually HD DVD and sometimes Blu-Ray is often branded with "Dolby Digital Plus" and/or "DTS-HD" logos.

Layout variation for 7.1 widescreen cinema format:

• Four channels for speakers at the front—left (L), Center-left (CL), right (R) and Center-Right (CR).
• One channel for speaker at the center—center (C).
• Two channels for surround speakers at the rear—surround left (LS) and surround right (RS).
• One low-frequency effects channel (LFE).

This variation is becoming increasingly popular in home entertainment systems, as well as for large cinema auditoria where the screen width is such that the additional channels are needed to cover all angles between the loudspeakers satisfactorily for all seats in the auditorium.

For music, speaker placement is unknown.

Placement: The front speakers should be placed at the edges of the screen, toed in to face the central listening location, and the tweeters should be ear height. The center speaker should be placed behind the screen (when using projection) or over or under a TV, and as close to ear height as possible. Side channel speakers should be placed on side walls, to the left and right of the listening position, equidistant from the front speakers and the rear speakers. Rear channel speakers should be placed on side walls, slightly behind the listening position, and should have a normal high-quality monopolar construction.

10.2 Channel Surround

10.2 is the surround sound format developed by THX creator Tomlinson Holman of TMH Labs and University of Southern California (schools of Cinema/Television and Engineering). Developed along with Chris Kyriakakis of the USC Viterbi School of Engineering, 10.2 refers to the format's promotional slogan: "Twice as good as 5.1". Advocates of 10.2 argue that it is the audio equivalent of IMAX.

10.2 augments the LS (left surround) and RS (right surround) channels by two point surround channels that can more finely manipulate sound—allowing the mixer to shift sounds in a distinct 360° circle around the movie watcher.

The 14 discrete channels are:

• Five front speakers: Left Wide, Left, Center, Right and Right Wide
• Five surround channels: Left Surround Diffuse, Left Surround Direct, Back Surround, Right Surround Diffuse and Right Surround Direct
• Two LFE channels: LFE Left, LFE Right
• Two Height channels: Left Height, Right Height

The .2 of the 10.2 refers to the addition of a second subwoofer. The system is bass managed such that all the speakers on the left side use the left sub and all the speakers on the right use the right sub. The Center and Back Surround speaker are split among the two subs. The two subs also serve as two discrete LFE (Low Frequency Effects) channels. Although low frequencies are not localizable, it was found that splitting the bass on either side of the audience increases the sense of envelopment.

22.2 Channel Surround

22.2 is the surround sound component of Ultra High Definition Video (Super Hi-vision TV with 4320 scanning lines), and has been developed by NHK Science & Technical Research Laboratories. As its name suggests, it uses 24 speakers. These are arranged in three layers: A middle layer of ten speakers, an upper layer of nine speakers, and a lower layer of three speakers and two sub-woofers. The system was demonstrated at Expo 2005, Aichi, Japan, the NAB 2006 conference, Las Vegas, and at IBC 2006, Amsterdam, Netherlands.

Infinite Channel Surround (Ambisonics)

Ambisonics is a series of recording and replay techniques using multichannel mixing technology that can be used live or in the studio. Any number of speakers in any physical arrangement can be used to recreate a sound field. With 6 or more speakers arranged around a listener, a 3-dimensional ("periphonic", or full-sphere) sound field can be presented. Ambisonics was invented by Michael Gerzon (among other researchers) of the Mathematical Institute, Oxford.

Panor-Ambiophonic (PanAmbio) 4.0/4.1

PanAmbio combines a stereo dipole and crosstalk cancellation in front and a second set in back of the listener (total of four speakers) for 360° 2D surround reproduction. Four channel recordings, especially those containing binaural cues, create speaker-binaural surround sound. 5.1 channel recordings, including movie DVDs, are compatible by mixing C-channel content to the front speaker pair. 6.1 can be played by mixing SC to the back pair.

Notation

This notation, e.g. "5.1", reflects the number of full range 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, as it strictly means "solid" sound. However this is no longer a common usage and "stereo sound" is almost exclusively used to describe two channel left and right sound.

See also

• 3D audio effect
• Acousmonium
• Ambisonics
• Aurophonie
• Birmingham ElectroAcoustic Sound Theatre
• Cinema Digital Sound
• DTS
• Dolby
• DVD-Audio
• Four channel compact disc digital audio
• Haas effect
• Iosono
• Matrix Decoder
• MP3 Surround
• MPEG Surround
• Penteo
• Quadraphonic
• Super Audio CD
• Sound card
• Soundfield microphone
• SRS Labs
• Surround Sound Test CD
• Virtual surround
• Wave field synthesis
• 8 channel audio

References

External links

• Ambisonia.com (Repository for surround sounds)

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