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Dolby DigitalA family of digital audio encoding technologies from Dolby used in movie theaters, home theaters and video games. Introduced in the movie "Batman Returns" in 1992, Dolby Digital has been the most widely used surround sound system in the world. Following are the major formats. See Dolby Surround and surround sound.
Dolby Digital - 5.1 Channels
Five discrete channels of audio plus subwoofer (see surround sound). Dolby Digital employs Dolby's AC-3 coding and compression technology (see AC-3).
Dolby Digital EX - 6.1 and 7.1 Channels
Co-developed with Lucasfilm THX, Dolby Digital EX adds one or two matrixed rear center channels. Formerly "Dolby Digital Surround EX," the first film to use this enhanced version of Dolby Digital was "Star Wars: Episode I - The Phantom Menace," in 1999.
Dolby Digital Plus - 6.1 and 7.1 Channels
Part of the Blu-ray specification, Dolby Digital Plus supports higher bit rates than EX. Also called "DD+" and "Enhanced AC-3" (E-AC-3).
Dolby TrueHD - 7.1 on Blu-ray
Providing up to 14 discrete sound channels in the complete specification, TrueHD used in Blu-ray movies delivers stereo at 192 kHz and up to eight channels (7.1) at 96 kHz. Introduced in 2006, Dolby TrueHD competes with DTS-HD for high-definition Blu-ray audio formats. HDMI 1.3 cables are required. See Blu-ray, DTS and HDMI.
Dolby Atmos - 9.1 Channels
Introduced in 2012, Atmos supports 128 audio tracks and up to 64 speakers in the cinema, although home theaters require at least a 5.1 system plus two "height speakers" that can either be ceiling mounted or "upward firing." Transformers: Age of Extinction was the first Atmos Blu-ray movie. Touted as "object-based surround sound," rather than "front and back surround," DTS:X was introduced with a similar approach (see DTS).