5.1 Surround Sound

5.1 surround sound ("five point one") is the common name for six channel surround sound audio systems. 5.1 is the most commonly used layout in home cinema. It uses five full bandwidth channels and one low-frequency effects channel (the "point one").Dolby Digital, Dolby Pro Logic II, DTS, SDDS, and THX are all common 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, two surround channels and a subwoofer.

A prototype for five-channel surround sound, then dubbed "quintaphonic sound", was used in the 1975 film Tommy.

5.1 dates back to 1976 when Dolby Labs modified the track usage of the six analogue magnetic soundtracks on Todd-AO 70 mm film prints. The Dolby application of optical matrix encoding in 1976 (released on the film, Logan's Run) did not use split surrounds, and thus was not 5.1. Dolby's first use of split surrounds was with 70mm film, which received wide release in 1979 with Apocalypse Now. Instead of the five screen channels and one surround channel of the Todd-AO format, Dolby Stereo 70 mm Six Track provided three screen channels, two high-passed surround channels and a low-frequency surround channel monophonically blended with the two surround channels.

When digital sound was applied to 35 mm release prints, starting with Batman Returns in 1992, the 5.1 layout was adopted. The ability to provide 5.1 sound had been one of the key reasons for using 70 mm for prestige screenings. The provision of 5.1 digital sound on 35 mm significantly reduced the use of the very expensive 70 mm format. Digital sound and the 5.1 format were introduced in 1990, by KODAK and Optical Radiation Corporation, with releases of "Days of Thunder" and "The Doors" using the CDS (Cinema Digital Sound) format.

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