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 . contents 1 in the cinema 2 versions 2.1 dolby digital 2.2 dolby digital ex 2.3 dolby digital surround ex 2.4 dolby digital live 2.5 dolby digital plus 2.6 dolby truehd 3 channel configurations 4 applications 5 dolby technologies in packaged media formats 6 technical details 7 liba52 8 license 9 see also 10 references 11 external links in the cinema edit this section does not cite any sources . please help improve this section by adding citations to reliable sources . unsourced material may be challenged and removed . september 2011 learn how and when to remove this template message batman returns was the first film to use dolby digital technology when it premiered in theaters in the summer of 1992 . 1 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 is then 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 . a dolby digital penthouse soundhead mounted on a mid 50s vintage kalee model 20 projector a photo of a 35 mm film print featuring all four audio formats or quad track from left to right sony dynamic digital sound sdds blue area to the left of the sprocket holes dolby digital grey area between the sprocket holes labelled with the dolby double d logo in the middle analog optical sound the two white lines to the right of the sprocket holes and the dts time code the dashed line to the far right . the simplest way of converting existing projectors is to add a so called penthouse digital soundhead above the projector head . however for new projectors it made sense to use dual analogue digital soundheads in the normal optical soundhead position under the projector head . to allow for the dual soundhead arrangement the data is recorded 26 frames ahead of the picture . if a penthouse soundhead is used the data must be delayed in the processor for the required amount of time around 2 seconds . this delay can be adjusted in steps of the time between perforations approximately 10.4 ms . as of 2015 update dolby digital in the cinema is being gradually replaced with dolby surround 7.1 a process that may take up to 2018 to complete . versions edit dolby digital 2 has similar technologies included in dolby digital ex 3 dolby digital live 4 dolby digital plus 5 dolby digital surround ex 6 dolby digital recording 7 dolby digital cinema 8 dolby digital stereo creator 9 and dolby digital 5.1 creator . 10 dolby digital edit dolby digital logo that is sometimes shown at the start of broadcasts feature films and video games the former dolby digital logo dolby digital is the common version containing up to six discrete channels of sound . the most elaborate mode in common use involves five channels for normal range speakers 20 hz 20 000 hz right center left right surround left surround and one channel 20 hz 120 hz allotted audio for the subwoofer driven low frequency effects . 11 mono and stereo modes are also supported . ac 3 supports audio sample rates up to 48 khz . the laserdisc version of clear and present danger featured the first home theater dolby digital mix in 1995 . citation needed this format has different names dolby digital dd an abbreviation for dolby digital often combined with channel count ; for instance dd 2.0 dd 5.1 ac 3 audio codec 3 advanced codec 3 acoustic coder 3 . these are backronyms . adaptive transform acoustic coding 3 is a separate format developed by sony . 12 atsc a 52 name of the standard 13 dolby digital ex edit dolby digital ex is similar in practice to dolby s earlier pro logic format which utilized matrix technology to add a center surround channel and single rear surround channel to stereo soundtracks . ex adds an extension to the standard 5.1 channel dolby digital codec in the form of matrixed rear channels creating 6.1 or 7.1 channel output . dolby digital surround ex edit the cinema version of dolby digital ex is called dolby digital surround ex and works similarly . it was co developed by dolby and lucasfilm thx in time for the release in may 1999 of star wars episode i the phantom menace . it provides an economical and backwards compatible means for 5.1 soundtracks to carry a sixth center back surround channel for improved localization of effects . the extra surround channel is matrix encoded onto the discrete left surround and right surround channels of the 5.1 mix much like the front center channel on dolby pro logic encoded stereo soundtracks . the result can be played without loss of information on standard 5.1 systems or played in 6.1 or 7.1 on systems with surround ex decoding and added speakers . dolby digital surround ex has since been used for the star wars prequels on the dvd versions and also the remastered original star wars trilogy . a number of dvds have a dolby digital surround ex audio option . a dolby home theater badge on a laptop dolby digital live edit dolby digital live ddl is a real time encoding technology for interactive media such as video games . it converts any audio signals on a pc or game console into a 5.1 channel 16 bit 48 khz dolby digital format at 640 kbit s and transports it via a single s pdif cable . 14 a similar technology known as dts connect is available from competitor dts . an important benefit of this technology is that it enables the use of digital multichannel sound with consumer sound cards which are otherwise limited to digital pcm stereo or analog multichannel sound because s pdif over rca bnc and toslink can only support two channel pcm dolby digital multichannel audio and dts multichannel audio . hdmi was later introduced and it can carry uncompressed multichannel pcm lossless compressed multichannel audio and lossy compressed digital audio . however dolby digital live is still useful with hdmi to allow transport of multichannel audio over hdmi to devices that are unable to handle uncompressed multichannel pcm . dolby digital live is available in sound cards using various manufacturers audio chipsets . the soundstorm used for the xbox game console and certain nforce2 motherboards used an early form of this technology . ddl is available on motherboards with codecs such as realtek s alc882d 15 alc888dd and alc888h . other examples include some c media pci sound cards and creative labs x fi and z series sound cards whose drivers have enabled support for ddl . nvidia later decided to drop ddl support in their motherboards due to the cost of involved royalties leaving an empty space in this regard in the sound cards market . then in june 2005 came auzentech which with its x mystique pci card provided the first consumer sound card with dolby digital live support . initially no creative x fi based sound cards supported ddl 2005 2007 but a collaboration of creative and auzentech resulted in the development of the auzentech prelude the first x fi card to support ddl . originally planned to extend ddl support to all x fi based sound cards except the xtreme audio line which is incapable of ddl hardware implementation the plan was dropped because dolby licensing would have required a royalty payment for all x fi cards and problematically those already sold . 16 in 2008 creative released the x fi titanium series of sound cards which fully supports dolby digital live while leaving all pci versions of creative x fi still lacking support for ddl . since september 2008 all creative x fi based sound cards support ddl except the xtreme audio and its based line such as prodigy 7.1 e which is incapable of ddl in hardware . x fi s case differs . while they forgot about the plan programmer daniel kawakami made a hot issue by applying auzentech prelude ddl module back to creative x fi cards by disguising the hardware identity as auzentech prelude . 17 creative labs alleged kawakami violated their intellectual property and demanded he cease distributing his modified drivers . 17 18 19 eventually creative struck an agreement with dolby laboratories regarding the dolby license royalty by arranging that the licensing cost be folded into the purchase price of the creative x fi pci cards rather than as a royalty paid by creative themselves . 16 based on the agreement in september 2008 creative began selling the dolby digital live packs enabling dolby digital live on creative s x fi pci series of sound cards . it can be purchased and downloaded from creative . subsequently creative added their dts connect pack to the ddl pack at no added cost . 20 dolby digital plus edit main article dolby digital plus e ac 3 dolby digital plus is an enhanced coding system based on the ac 3 codec . it offers increased bitrates up to 6.144 mbit s support for more audio channels up to 13.1 and improved coding techniques only at low data rates to reduce compression artifacts enabling lower data rates than those supported by ac 3 e.g. 5.1 channel audio at 256 kbit s . it is not backward compatible with existing ac 3 hardware though e ac 3 codecs generally are capable of transcoding to ac 3 for equipment connected via s pdif . e ac 3 decoders can also decode ac 3 bitstreams . the fourth generation apple tv supports e ac 3 . 21 the discontinued hd dvd system directly supported e ac 3 . blu ray disc offers e ac 3 as an option to graft added channels onto an otherwise 5.1 ac 3 stream as well as for delivery of secondary audio content e.g. director s commentary that is intended to be mixed with the primary audio soundtrack in the blu ray disc player . dolby truehd edit main article dolby truehd dolby truehd developed by dolby laboratories is an advanced lossless audio codec based on meridian lossless packing . support for the codec was mandatory for hd dvd and is optional for blu ray disc hardware . dolby truehd supports 24 bit 96 khz audio channels at up to 18 mbit s over 14 channels hd dvd and blu ray disc standards currently limit the maximum number of audio channels to eight . it supports metadata including dialog normalization and dynamic range control . channel configurations edit although commonly associated with the 5.1 channel configuration dolby digital allows a number of different