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.

Dolby Atmos

Dolby Atmos is the name of a surround sound technology announced by Dolby Laboratories in April 2012 and released in June of the same year, first utilized in Pixar's Brave.

History

The first installation was in the Dolby Theater in Hollywood, California, for the premiere of Brave in June 2012. Throughout 2012, it saw a limited release of about 25 installations worldwide, with an increase to 300 locations in 2013. There were over 2,100 locations as of February 2015. Dolby Atmos has also been adapted to a home theatre format.

Technology

The Dolby Atmos technology allows up to 128 audio tracks plus associated pan metadata to be distributed to theaters for optimal, dynamic rendering to loudspeakers based on the theater capabilities. That is, Dolby Atmos enables the re-recording mixer using a Pro Tools plugin (available from Dolby) or a Dolby Atmos equipped large format audio mixing console such as AMS Neve's DFC or Harrison's MPC5, to designate a particular location in the theater, as a three-dimensional placement, where each dynamic sound source should seem to be coming from. Sounds that are not dynamically moving, such as ambient sounds and center dialogues, are still separately pre-mixed in a traditional multichannel format. During playback, each theater's Dolby Atmos system renders all dynamic sounds, from the pan metadata, in real-time to make it seem like each sound is coming from its designated spot, with respect to the speakers present in the target theater. By way of contrast, traditional multichannel technology essentially burns the audio tracks into a fixed number of channels during post-production. This has traditionally forced the re-recording mixer to make up-front assumptions about the playback environment that may not apply very well to a particular theater (to the extent its capabilities differ from the mixing stage where the mixer was working).

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.

7.1 surround sound

7.1 sound is the common name for an eight-channel surround audio system commonly used in home theatre configurations. It adds two additional speakers to the more conventional six-channel (5.1) audio configuration. As with 5.1 surround sound, 7.1 surround sound positional audio uses the standard front, center, and LFE (subwoofer) speaker configuration. However, whereas a 5.1 surround sound system combines both surround and rear channel effects into two channels (commonly configured in home theatre set-ups as two rear surround speakers), a 7.1 surround system splits the surround and rear channel information into four distinct channels, in which sound effects are directed to left and right surround channels, plus two rear surround channels. In a 7.1 surround sound home theatre set-up, the surround speakers are placed to the side of the listener's position and the rear speakers are placed behind the listener. In addition, with the advent of Dolby Pro Logic IIz and DTS Neo:X, 7.1 surround sound can also refer to 5.1 surround sound configurations with the addition of two front height channels positioned above the front channels or two front wide channels positioned between the front and surround 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.