Editing Dolby Digital (section)

== Cinema ==
{{update|inaccurate=y|date=September 2020}}
''[[Batman Returns]]'' was the first movie to be announced as using Dolby SR-D (Spectral Recording-Digital) technology when it premiered in all selected movie theaters in the summer of 1992.<ref>{{cite news |url=https://www.nytimes.com/1992/08/12/business/company-news-a-sound-idea-dolby-theater-format-adapted-to-home-uses.html?ref=dolbylaboratoriesinc |title=COMPANY NEWS: A Sound Idea; Dolby Theater Format Adapted to Home Uses |newspaper=[[The New York Times]]|date=12 August 1992 |last1=Fisher |first1=Lawrence M. }}</ref> Dolby Digital cinema soundtracks are optically recorded on a [[35 mm movie film|35 mm]] [[release print]] using sequential data blocks placed between every perforation hole on the soundtrack side of the film. A constant bit rate of {{nowrap|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]] analog soundtracks using Dolby SR noise reduction and such prints are known as Dolby SR-D prints. The analog 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 modern cinema prints are of this type and may also include [[SDDS]] data and a timecode track to synchronize CD-ROMs carrying [[DTS (sound system)|DTS]] soundtracks.
[[File:Dolby Digital track reader.jpg|thumb|left|A Dolby Digital Penthouse Soundhead mounted on a mid-1950s vintage Kalee model 20 projector]]
[[File:35mm film audio macro.jpg|thumb|right|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, Inc.|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 analog/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).

Dolby Digital remains the predominant sound mixing format for movies, despite the introduction of [[Dolby Surround 7.1]] and [[Dolby Atmos]] in 2010 and 2012, respectively.