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, and SDDS 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.

History

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 1976 (released on the film, Logan's Run) did not use split surrounds, and thus was not 5.1. Dolby's use of split surrounds, and the introduction of the 5.1 format on optical prints started 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 surround channels and a low-frequency enhancement channel.

Surround sound

Surround sound is a technique for enriching the sound reproduction quality of an audio source with additional audio channels from speakers that surround the listener (surround channels), providing sound from a 360° radius in the horizontal plane (2D) as opposed to "screen channels" (centre, [front] left, and [front] right) originating only from the listener's forward arc.

Surround sound is characterized by a listener location or sweet spot where the audio effects work best, and presents a fixed or forward perspective of the sound field to the listener at this location. The technique enhances the perception of sound spatialization by exploiting sound localization; a listener's ability to identify the location or origin of a detected sound in direction and distance. Typically this is achieved by using multiple discrete audio channels routed to an array of loudspeakers.

There are various surround sound based formats and techniques, varying in reproduction and recording methods along with the number and positioning of additional channels.

Dolby Digital

Dolby Digital is the name for audio compression technologies developed by Dolby Laboratories. It was originally named 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. It is now also used for other applications such as HDTV broadcast, DVDs, Blu-ray Discs and game consoles.

In the cinema

Batman Returns was the first film to use Dolby Digital technology when it premiered in theaters in the summer of 1992. Dolby Digital cinema soundtracks are optically recorded on a 35 mm release print using sequential data blocks placed between every perforation hole on the sound track side of the film. A constant bit rate of 320 kbit/s is used. A charge-coupled device (CCD) scanner in the image projector picks up a scanned video image of this area, and a processor correlates the image area and extracts the digital data as an AC-3 bitstream. The data are finally decoded into a 5.1 channel audio source. All film prints with Dolby Digital data also have Dolby Stereo analogue soundtracks using Dolby SR noise reduction and such prints are known as Dolby SR-D prints. The analogue soundtrack provides a fall-back option in case of damage to the data area or failure of the digital decoding; it also provides compatibility with projectors not equipped with digital soundheads. Almost all current release cinema prints are of this type and may also include SDDS data and a timecode track to synchronize CD-ROMs carrying DTS soundtracks.

Sound

In physics, sound is a vibration that propagates as a typically audible mechanical wave of pressure and displacement, through a medium such as air or water. In physiology and psychology, sound is the reception of such waves and their perception by the brain.

Acoustics

Acoustics is the interdisciplinary science that deals with the study of mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound, and infrasound. A scientist who works in the field of acoustics is an acoustician, while someone working in the field of acoustical engineering may be called an acoustical engineer. An audio engineer, on the other hand is concerned with the recording, manipulation, mixing, and reproduction of sound.

Applications of acoustics are found in almost all aspects of modern society, subdisciplines include aeroacoustics, audio signal processing, architectural acoustics, bioacoustics, electro-acoustics, environmental noise, musical acoustics, noise control, psychoacoustics, speech, ultrasound, underwater acoustics, and vibration.

Home theater

A home theater or home theatre is a theater built in a home, designed to mimic (or exceed) commercial theater performance and feeling, more commonly known as a home cinema. Today, home cinema implies a real "cinema experience" at a private home.