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Surround sound encompases a range of techniques for enriching the sound reproduction quality of an audio source with 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 cinema and home theater systems, video game consoles, personal computers and other platforms. Commercial surround sound media 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 and DTS. Sony Dynamic Digital Sound (SDDS) is a 7.1 Cinema configuration which features 5 independent audio channels across the front with two independent surround channels, and an LFE.

Most surround sound recordings are created by film production companies or video game producers; however some consumer camcorders have such capability either built-in or available separately. Surround sound technologies can also be used in music to enable new methods of artistic expression. After the failure of quadraphonic audio in the 1970s, multichannel music has slowly been reintroduced since 1999 with the help of SACD and 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.

In 1967 the rock group Pink Floyd performed the first-ever surround sound concert at “Games for May”, a lavish affair at London’s Queen Elizabeth Hall where the band debuts its custom-made quadraphonic speaker system.[1]

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 using fully discrete and rotating quadraphonic sounds generated with industrial electronic equipment in Herbert Eimert's studio at the Westdeutscher Rundfunk (WDR). Edgar Varese's Poeme Electronique, created for the Iannis Xenakis designed Philips Pavilion at the 1958 Brussels World's Fair, also utilised spatial audio with 425 loudspeakers used to move sound throughout the pavilion. 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 in 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 wave fronts within the listening space; an "audio hologram" form. One form, wave field synthesis (WFS), produces a sound field with an even error field over the entire area. Commercial WFS systems, currently marketed by 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. [2] Some years ago it was shown that, in the limit, WFS and Ambisonics converge.[3]

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. There are however more ways to create surround out of stereo, for instance with routines based on the QS and SQ Quad routines, where instruments were in the studio divided over 4 speakers. This way of creating surround with softwareroutines is normally referred to as "upmixing". [4]

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 – one renders a sound field as produced by a set of speakers, analogously to rendering in computer graphics. 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

Because the Low Frequency Effects channel requires only one-tenth of the bandwidth of the other audio channels, it is referred to as the ".1" channel; for example "5.1" or "7.1". LFE is sometimes expanded as Low-frequency Enhancement.[5]

The 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 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.[6]

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. The label BIS generally uses a 5.0 channel mix.

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.

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. 2 basic stereo speakers with no LFE channel = 2.0
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.

Standard speaker channels

Channel name Identifier Index Flag 1.0 Mono* 2.0 Stereo** 2.1 Stereo** 4.0 Surround 4.0 Quad 4.1 5.1 5.1 Side*** 6.1 7.1 Front 7.1 Surround
Front Left SPEAKER_FRONT_LEFT 0 0x00000001 No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes
Front Right SPEAKER_FRONT_RIGHT 1 0x00000002 No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes
Front Center SPEAKER_FRONT_CENTER 2 0x00000004 Yes No No Yes No No Yes Yes Yes Yes Yes
Low Frequency SPEAKER_LOW_FREQUENCY 3 0x00000008 No No Yes No No Yes Yes Yes Yes Yes Yes
Back Left SPEAKER_BACK_LEFT 4 0x00000010 No No No No Yes Yes Yes No Yes Yes Yes
Back Right SPEAKER_BACK_RIGHT 5 0x00000020 No No No No Yes Yes Yes No Yes Yes Yes
Front Left of Center SPEAKER_FRONT_LEFT_OF_CENTER 6 0x00000040 No No No No No No No No No Yes No
Front Right of Center SPEAKER_FRONT_RIGHT_OF_CENTER 7 0x00000080 No No No No No No No No No Yes No
Back Center SPEAKER_BACK_CENTER 8 0x00000100 No No No Yes No No No No Yes No No
Side Left SPEAKER_SIDE_LEFT 9 0x00000200 No No No No No No No Yes No No Yes
Side Right SPEAKER_SIDE_RIGHT 10 0x00000400 No No No No No No No Yes No No Yes

The table above shows the various speaker configurations that are commonly used for end-user equipment. The order and identifiers are those specified for the channel mask in the standard uncompressed WAV file format (which contains a raw multichannel PCM stream) and are used according to the same specification for most PC connectible digital sound hardware and PC operating systems capable of handling multiple channels [7]. While it is certainly possible to build any speaker configuration, there isn't a lot of commercially available movie or music content for alternative speaker configurations. Such cases, however, can be worked around by remixing the source content channels to the speaker channels using a matrix table specifying how much of each content channel is played trough each speaker channel. For interactive entertainment such as games, on the other hand, if your platform (be that your console, or operating system) enables you to manually specify the role for each speaker in your sound system, it is perfectly possible to have any speaker configuration imaginable, as the audio sources are dynamically panned based on the speaker configuration information supplied by the operating system (by means of the channel mask), and not mixed in advance on a pre-specified configuration.

(*) For historical reasons, when using (1.0) mono sound, often in technical implementations the first (left) channel is used, instead of the center speaker channel, in many other cases when playing back multi-channel content on a device with a mono speaker configuration all channels are downmixed into one channel. The way standard mono and stereo plugs used for common audio devices are designed ensures this as well.

(**) Stereo (2.0) is still the most common format for music, as most computers, television sets and portable audio players only feature two speakers, and the red book Audio CD standard used for retail destribution of music only allows for 2 channels. A 2.1 speaker set does generally not have a separate physical channel for the low frequency effects, as the speaker set downmixes the low frequency components of the two stereo channels into one channel for the subwoofer.

(***) Some people prefer to have speakers on the side instead of behind them. This is more practical in smaller rooms where you still want to sit as far away from the screen as possible, but it does sacrifice the effect of sounds coming from behind the viewer, resulting in a less than optimal sound experience. While technically the side channels and back channels are separately specified, it is generally desirable that when playing any sort of discreet 5.1 content, the side channels can be automatically remapped to the back channels and vice versa. The difference between side and back channels is more important to be correctly set up when downmixing for example 7.1 content or when the content played back is interactively panned in 3d space on the end-user's system.

Channel identification

In accordance with ANSI/CEA-863-A[8]

Zero-based order within multi-channel
mp3/flac datastream[9][10]
Order within
wav[11]
Order within
DTS/AAC[12][13]
Channel name Color-coding on commercial receiver and cabling
0 0 1 Front left White
1 1 2 Front right Red
2 2 0 Center Green
3 3 5 Low frequency Purple
4 9 3 Surround left Blue
5 10 4 Surround right Grey
6 4 6 Surround back left Brown
7 5 7 Surround back right Khaki

Sonic Whole Overhead Sound

In 2002, Dolby premiered a master of We Were Soldiers which featured a Sonic Whole Overhead Sound soundtrack. This mix included a new ceiling-mounted height channel.

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 12 discrete channels are:

Sound-10 2.svg
  • 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 Shows 2006 & 2009, Las Vegas, and the IBC trade shows 2006 & 2008, Amsterdam, Netherlands.

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 and others.

Panor-Ambiophonic (PanAmbio) 4.0/4.1

PanAmbio combines a stereo dipole and crosstalk cancellation in front and a second set behind 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.

See also

References

External links

  • MM-News.org, Multichannel Music News
  • Audio4Fun.com, Create Surround Sound - Exploit all speakers of a multi-channel system







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