Surround sound


Surround sound

Surround sound, using multichannel audio, encompasses a range of techniques for enriching (expanding and deepening) the sound reproduction quality, of an audio source, with additional audio channels reproduced via additional, discrete speakers. The three-dimensional (3D) sphere of human hearing can be virtually achieved with audio channels above and below the listener. To that end, the multichannel surround sound application encircles the audience (left-surround, right-surround, back-surround), as opposed to "screen channels" (center, [front] left, and [front] right), i.e. ca. 360° horizontal plane, 2D).

Surround sound technology is used in both cinema and "home theater" systems, video game consoles, and personal computers, et cetera. Commercial surround sound formats include videocassettes, Video DVDs, and HDTV broadcasts encoded as Dolby Pro Logic, Dolby Digital, or DTS. Other commercial formats include the competing DVD-Audio (DVD-A) and Super Audio CD (SACD) formats; and MP3 Surround. Cinema 5.1 surround formats include Dolby Digital, DTS, and Sony Dynamic Digital Sound (SDDS).

Mostly, film production companies and video game creators are the principal users of surround sound; however, some consumer camcorders have such capability, either in-built or discrete. Also these technologies can be found in music, where it gives new methods for author's intends expression. After quadraphonic failure in seventies, multichannel music slowly rises since 1999 with help of SACD & DVD-Audio formats. Some AV receivers, stereophonic systems, and computer soundcards contain integral digital signal processors and / or digital audio processors to simulate surround sound from a stereophonic source.

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History

The first, documented use of surround sound was in 1940, for the Disney studio's animated film "Fantasia". Its multichannel audio application was called 'Fantasound', comprising three audio channels and speakers; the sound was diffused throughout the cinema, initially, by an engineer using some 54 loudspeakers; the surround sound was achieved using the sum and the difference of the phase of the sound. In the 1950s, the German composer Karlheinz Stockhausen experimented with and produced ground-breaking electronic compositions such as "Gesang der Jünglinge" and "Kontakte", the latter of which used fully discrete and rotating quadraphonic sounds generated with industrial electronic equipment in Herbert Eimert's studio at the "Westdeutscher Rundfunk" (WDR). Iannis Xenakis also created an electronic surround-sound work for the Philips Pavilion at the Paris World's Fair on which he collaborated with the architect Le Corbusier, and there are also many other composers that created ground-breaking surround-sound works in the same time period.

Creating surround sound

Surround sound is created several ways. The first, and simplest, method is using a surround sound recording microphone technique and / or mixing-in surround sound for playback on an audio system using speakers — encircling the listener — to play audio from different directions. A second approach is processing the audio with psychoacoustic sound localization methods to simulate a two-dimensional (2-D) sound field with headphones. A third approach, based on Huygens' principle, attempts reconstructing the recorded sound field wavefronts within the listening space, an "audio hologram" form. One form, wave field synthesis (WFS), produces a soundfield with an even error field over the entire area. Commercial WFS systems, made by the Swiss companies "sonic emotion" and "Iosono", require many loudspeakers and significant computing power.

The Ambisonics form, also based on Huygens' principle, gives an exact sound reconstruction at the central point; less accurate away from center point. There are many free and commercial software available for Ambisonics, which dominates most of the consumer market, especially musicians using electronic and computer music. Moreover, Ambisonics products are the standard in surround sound hardware sold by Meridian Audio, Ltd. In its simplest form, Ambisonics consumes few resources, however, this is not true for recent developments, such as Near Field Compensated Higher Order Ambisonics. [ [http://gyronymo.free.fr/audio3D/publications/AES23%20NFC%20HOA.pdf Spatial Sound Encoding Including Near Field Effect: Introducing Distance Coding Filters and a Viable, New Ambisonic Format] ] Some years ago it was shown that, in the limit, WFS and Ambisonics converge. [ [http://www.iua.upf.es/dafx98/papers/ROZ31.PS Further Investigations of High Order Ambisonics and Wavefield Synthesis for Holophonic Sound Imaging] ]

Finally, surround sound also can be achieved by mastering level, from stereophonic sources as with Penteo, which uses FFT analysis of a stereo recording to parse out individual sounds to component panorama positions, then positions them, accordingly, into a five-channel field.

Mapping channels to speakers

In most cases, surround sound systems rely 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 sound, the transmission medium allows for (at least) the same number of channels of source and destination; however, one-to-one, channel-to-speaker, mapping is not the only way of transmitting surround sound signals.

The transmitted signal might encode the information (defining the original sound field) to a greater or lesser extent; the surround sound information is "rendered" for replay by a decoder generating the number and configuration of loudspeaker feeds for the number of speakers available for replay. This "replay device independent" encoding is analogous to encoding and decoding an Adobe PostScript file, where the file describes the page, and is rendered per the output device's resolution capacity. The Ambisonics and WFS systems use audio rendering; the 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. [ [http://www.dolby.com/assets/pdf/tech_library/4_Multichannel_Music_Mixing.pdf Multichannel Music Mixing] by Dolby Laboratories, Inc.]

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 Enhancement". [Holman, T.,(2000) "5.1 Surround Sound: Up and Running"]

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. The decimal notation ( ex .1, .2 ) refers to the number of low-frequency effects channels (LFE). A fuller description of the notation is below.

3.0 Channel Surround (analog matrixed: Dolby Surround)

Extracts 3 audio channels from a specially encoded two-channel source:
*Two channels for speakers at the front—left (L) and right (R).
*One channel for surround speaker or speakers at the rear—surround (S).
*Describes the numerous matrixed (pre- Pro Logic) surround processors.

Placement: (three speakers in total) Three identical speakers placed equidistant around a central listening position. If two rear speakers are used they should also be placed above ear height, slightly behind the listening position, and should be of bi-polar construction.

4.0 Channel Surround (analog matrixed/discrete: Quadraphonic)

Extracts four audio channels from either a specially encoded two-channel source or a four-channel source:
*Two channels for speakers at the front—left (L) and right (R).
*Two channels for surround speakers at the rear—surround left (LS) and surround right (RS).
*Describes the early matrixed systems and discrete Quadraphonic surround systems. Source media, usually LP record or tape, is often branded four channel stereo.

Placement: Quadraphonics is a system designed for music only. All speakers should be at an ±45˚. All speakers should be above ear height.

4.0 Channel Surround (analog matrixed: Dolby Pro Logic)

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 above 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. [Rumsey, F., 2001 "Spatial Audio", Oxford, Focal Press, p.86]

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". [Rumsey, F., 2001 "Spatial Audio", Oxford, Focal Press, p.89]

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 discrete 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).
*Describes the Dolby Digital, Digital Theater System (DTS), and Sony Dynamic Digital Sound (SDDS) systems. Source media, usually DVD and sometimes Laser Disc or satellite/digital cable is often branded with "Dolby Digital" and/or DTS logos.
*DTS uses a higher data rate than Dolby Digital, so DTS can achieve higher fidelity. 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. [Rumsey, F., 2001 "Spatial Audio", Oxford, Focal Press, p.86]

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". [Rumsey, F., 2001 "Spatial Audio", Oxford, Focal Press, p.89]

6.1 Channel Surround (analog matrixed: Dolby Pro Logic IIx)

Extracts six audio channels and one low-frequency channel from either a specially encoded two-channel or stereo source. Expands a back surround channel from a 5.1 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 channel to drive a sub-woofer.
*Describes the Dolby Pro Logic IIx matrixed surround system. Source media is the same as both Dolby Pro Logic and Dolby Pro Logic II.

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. Front speakers should be at ear height and surrounds should be above.

6.1 Channel Surround (digital partially discrete: Dolby Digital EX)

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. Front speakers should be at ear height and surrounds should be above 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. Front speakers should be at ear height and surrounds should be above ear height.

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

:"See also: 8 channel audio"
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). [ [http://www.dolby.com/consumer/home_entertainment/roomlayout2.html Room Layout and Speaker Setup by Dolby Laboratories, Inc.] ]
*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 Blu-Ray and sometimes HD DVD 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. [Rumsey, F., 2001 Spatial Audio, Oxford, Focal Press, p.94]

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. Front speakers should be at ear height and surrounds should be above ear height.

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

*8 channel audio
*3D audio effect
*Ambisonics - Surround sound techniques
*Aurophonie - 3D surround sound
*Digital Theatre System - (DTS)
*Four channel compact disc digital audio
*Haas effect
*Iosono
*Matrix Decoder
*MP3 Surround
*MPEG Surround
*Penteo - Convert stereo to surround
*Quadraphonic
*Super Audio CD
*Soundfield microphone
*Virtual surround
*Wave field synthesis
*Dolby Surround

References

External links

* [http://www.ambisonia.com/ Ambisonia.com (Repository for surround sounds)]
* [http://www.mm-news.org/ Multichannel Music News]


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