5.1 surround sound
Encyclopedia
5.1 ("five point one") is the common name for six channel surround sound
Surround sound
Surround sound encompasses a range of techniques such as for enriching the sound reproduction quality of an audio source with audio channels reproduced via additional, discrete speakers. Surround sound is characterized by a listener location or sweet spot where the audio effects work best, and...

multichannel audio systems. 5.1 is now the most commonly used layout in both commercial cinemas and home theater
Home theater
A home theater or home theatre is a theater built in a home, designed to mimic commercial theater performance and feeling, more commonly known as a home cinema...

s. It uses five full bandwidth channels and one low frequency enhancement channel (the "point one"). Dolby Digital
Dolby Digital
Dolby Digital is the name for audio compression technologies developed by Dolby Laboratories. It was originally called Dolby Stereo Digital until 1994. Except for Dolby TrueHD, the audio compression is lossy. The first use of Dolby Digital was to provide digital sound in cinemas from 35mm film prints...

, Dolby Pro Logic II, DTS, and SDDS are all commonly 5.1 systems. 5.1 is also the standard surround sound audio component of digital broadcast and music.

All 5.1 systems use the same speaker channels and configuration, having a front left and right, a center channel
Center channel
Center channel refers to an audio channel common to many surround sound formats. It is the channel that is mostly, or fully, dedicated to the reproduction of the dialogue of an audiovisual program...

, and two surround channels
Surround channels
Surround channels are audio channels in surround sound multichannel audio. They primarily serve to deliver ambience and diffuse sounds in a film or music soundtrack...

.

History

5.1 dates back to the 1970s (1976) when Dolby Labs modified the track usage of the six analogue magnetic soundtracks on Todd-AO 70mm film prints. Instead of the 5 screen channels and one surround channel of the Todd-AO format, Dolby Stereo 70 mm Six Track provided three screen channels, two surround channels and a low-frequency enhancement channel.

When digital sound was applied to 35mm release prints, starting with Batman Returns
Batman Returns
Batman Returns is a 1992 American superhero film directed by Tim Burton. Based on the DC Comics character Batman, it is the sequel to Burton's Batman , and features Michael Keaton reprising the title role, with Danny DeVito as the Penguin and Michelle Pfeiffer as Catwoman.Burton originally did not...

in 1992, the same 5.1 layout was adopted. The ability to provide 5.1 sound had been one of the key reasons for using 70mm for prestige screenings. The provision of 5.1 digital sound on 35mm significantly reduced the use of the very expensive 70mm format.

Digital 5.1 sound was later used on Laserdisc
Laserdisc
LaserDisc was a home video format and the first commercial optical disc storage medium. Initially licensed, sold, and marketed as MCA DiscoVision in North America in 1978, the technology was previously referred to interally as Optical Videodisc System, Reflective Optical Videodisc, Laser Optical...

 and DVD
DVD
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....

 starting with the Laserdisc version of Clear and Present Danger
Clear and Present Danger
Clear and Present Danger is a novel by Tom Clancy, written in 1989, and is a canonical part of the Jack Ryan universe. In the novel, Jack Ryan is thrown into the position of CIA Acting Deputy Director and discovers that he is being kept in the dark by his colleagues who are conducting a covert war...

in 1995. Blu-ray and Digital cinema
Digital cinema
Digital cinema refers to the use of digital technology to distribute and project motion pictures. A movie can be distributed via hard drives, optical disks or satellite and projected using a digital projector instead of a conventional film projector...

 both have eight-channel capability which can be used to provide either 5.1 or 7.1 surround sound. 7.1 is an extension of 5.1 that uses four surround zones: two at the sides and two at the back.

A system of digital 5.1 surround sound had also been used in 1987 at the famous Parisian Cabaret The Moulin Rouge
Moulin Rouge
Moulin Rouge is a cabaret built in 1889 by Joseph Oller, who also owned the Paris Olympia. Close to Montmartre in the Paris district of Pigalle on Boulevard de Clichy in the 18th arrondissement, it is marked by the red windmill on its roof. The closest métro station is Blanche.The Moulin Rouge is...

, created by French engineer Dominique Bertrand.
To achieve such a system, in 1985 a dedicated mixing console had to be designed in cooperation with Solid State Logic
Solid State Logic
Solid State Logic is a manufacturer of high-end mixing consoles and recording studio hardware headquartered in Begbroke, Oxfordshire, UK.- Company information :...

, based on their 5000 series, and dedicated speakers in cooperation with APG.
The console included ABCDEF channels. Respectively: A left, B right, C centre, D left rear, E right rear, F bass.
The same engineer had already developed a similar 3.1 system in 1973, for use at the official International Summit of Francophone States, in Dakar, Senegal.

Music

Regarding music the main goal of 5.1 surround sound is a proper localization and equability of all acoustic sources for a centered positioned audience. Therefore ideally five speakers of same dimension should be used.

For play-back of 5.1 music recommendations of the International Telecommunication Union (ITU) have been released and propose following configuration (ITU-R BS 775):
  • five speakers of same dimension for front, center and surround
  • identical distance of all five speakers to the audience
  • angle adjustment regarding viewing direction of audience: center 0°, front ±22.5° for movies ±30° for music, surround ±110°


Placing speakers to meet these requirements, in order to provide optimum sound quality, is often at odds with the space constraints of the average living room.
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