the Digital Revolution

Digital formats:

previous chapter: the Rise of the Dolby Empire

next chapter: a word on THX


Digital Fluorescentsound was one of the first attemps to add digital sound to movies. The digitally encoded soundtrack was placed on top of the picture. During normal projection the digital data was not visible on the screen. When the film was scanned with ultraviolet light, the track emitted a bright blue, visible, image that was picked up by a reader that replaced the penthouse for magnetic tracks. The gathered data was processed into 6 analog audio signals, ready for amplification. These signals had low or no distortion or noise. Digital Fluorescentsound was developed in 1981-'82 by Peter Custer and Dr. George Bird. They also patented the system but it was never really put into use.

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CDS (Cinema Digital Sound) : In the late 1980's Eastman Kodak Corporation joined forces with Optical Radiation Corporation to develop what would become the first commercially available digital sound format.
It was a sound-on-film system for 35mm and 70mm film formats with the digital information placed between the sprockets and the film frame, thus replacing the analog optical tracks on 35mm and the magstripes on 70mm releases. CDS featured 6 discrete audiochannels: 5 of them with full bandwith (Left, Center, Right, Left and Right Surround) and one low frequency only channel (LFE).
The compression technique used on CDS was Delta Modulation, a variation of standard 16-bit PCM coding. Instead of recording every sample to a 0dB level as PCM does, Delta Modulation records the difference in intensity between 2 successive samples. This method needs less than the 16 bits needed for a PCM sample and a compression ration of approximately 4:1 could be achieved without loss of information. The system used Reed-Solomon burst error correction with cyclic redundancy check character backup as an error correction and detection strategy. Besides the digital audio track a standard SMTP Time Code track was included to provide synchronization between the sound and the picure and a computer could control peripherals like lights and curtains using the MIDI (Musical Instrument Digital Interface) control channel.
Athough the system sounded great it quickly got the reputation of being faulty. Back in 1990, when the system was introduced, it was a pioneer in its field and LED and CCD technology (see How does digital sound-on-film work?) weren't as developed as they are now. Printing the dense digital track on the film proved to be a problem, too. As the digital soundtrack wasn't reliable, prints degrade anyway and hardware failures could occur, a second print, with analog sound, had to be kept ready at all times.
CDS debuted in June 1990 on 70mm film prints with release of "Dick Tracy" and in March 1991 on 35mm prints with "The Doors". In July 1991 "Terminator 2: Judgement Day" was released with CDS on both 70mm and 35mm; it was the sound system's brightest moment. But distributors were reluctant to release movies in CDS because of its playback problems and the expensive system couldn't convince theater owners enough. Also all releases had to be available in standard analog optical sound too as a back-up for the CDS release and for theaters not equipped with the digital system. Above that, Dolby Labs. announced in early 1991 their own digital format, Dolby Stereo SR Digital, more than a year before the actual release.
The last picture to feature a CDS soundtrack was "Final Approach" released in November 1991. The other movies released in CDS were "Days of Thunder" (6/1990, 70mm), "Flatliners" (10/1990, 70mm) and "Hudson Hawk" (5/1991, 35mm). "For the Boys" (11/1991) and "Universal Soldier" (7/1992) were announced to feature a CDS soundtrack but the actual releases had analog ones.

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L.C.Concept was the first digital sound-on-disk system available. The soundtrack was placed on 2 5"1/4 rewritable magneto-optical disks manufactured by Sony. The 2 disks were capable of storing 300MB of data each, equivalent to 90 minutes of soundtrack so the system could handle films of maximum 3 hours. The sound-mix with 4 or 5.1 discrete channels was compressed with the MUSICAM-algorithm (Masking Pattern Universal Subband Integrated Coding and Multiplexing). It was a variation on ISO/MPEG Layer 2 (MP2)lossy coding algorithm and provided a 6:1 compression ratio. The standard SMPTE time-code track, located on the analog soundtrack side of the film, provided synchronization. In order to avoid the need to restart the setting process each time the system was transferred to a other theater, several settings could be stored in the processor.
L.C.Concept, developed by Frenchman Pascal Chedeville, was first demonstrated in 1991 with a experimental re-release of the 1990 film "Cyrano de Bergerac". The first commercial release was done in late 1991 with "Bis ans Ende der Welt", only in France. In 1994 the system was modified for use with CD-ROMs instead of magneto-optical disks but it was never put to use commercially.
The system had no technical drawbacks (unlike CDS) but the L.C.Concept company failed in 1994 mainly because of a lack of financial strength caused by large companies not supporting the system in anticipation of Dolby's announced digital system in 1991. Pascal Chedeville received in 1995 an Technical Achievement Academy Award. In total some 20 theaters in France, Switzerland and Belgium were equipped with the system and about 30 films featured a L.C.Concept soundtrack.

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Dolby Digital : In 1987 Dolby Labs. began to work on a proposal for a sound system for HDTV (High Definition Television), the next generation TV system. At first it was it intended to harbour on 2 channels but by using new and advanced encoding schemes, it was possible to store up to 6 discrete channels of audio. (5 of them full width and 1 for low frequencies only). The preview Dolby Digital layoutsystem was named AC-3 (Audio Coder 3). Because HDTV wouldn't become available for commercial use for several years, Dolby Labs. used AC-3 for the development of a digital cinema sound system with the now standard 5.1-channel configuration of Left, Center, Right channels behind the screen, Left and Right Surround in the back of the theatre and one low frequency only channel (LFE).
It was decided to create a digital sound-on-film format with the digital track placed between preview Dolby Digital printthe sprockets instead of replacing the analog Dolby Stereo SR track, like CDS did. By keeping the analog track available the system had important advantages over CDS: the track could provide a back-up in case the digital system failed due to a damaged digital track or hardware failure. By putting the digital track between the sprockets, it's better protected against damage. Because both a digital and an analog track are located on one print, there was also no need to keep a double inventory. The format was compatible with all previous optical playback equipment if exhibitors chose not to upgrade.
The system, originally designated Dolby Stereo SR Digital (Dolby SR*D) but now known as Dolby Digital, was announced in early 1991 but the first movie to feature the new format was "Batman Returns" in 1992. By now Dolby Digital has become the de facto standard in digital audio as most releases with a digital soundtrack feature at least a Dolby SR*D one because the system has some advantages over competing formats DTS and SDDS. The sound-on-film system is more convenient than DTS' sound-on-disk and the reader and decoder are cheaper than SDDS.

Dolby Digital Surround EX : Early 1999 Dolby and Lucasfilm THX announced a further development of Dolby Digital. An extra channel would be added to the surrounds,preview Dolby Digital Surround-EX layout thus creating a 6.1-channel system. Gary Rydstrom, while working on the sound mix for "Star Wars: Episode I - The Phantom Menace", had proposed the new set-up because he felt that an extra rear channel could provide a better placement of effects sounds.
preview Dolby Digital Surround-EX printDolby Digital Surround EX's center surround-channel was encoded in the existing 2 surround channels by applying the same techniques as on with Dolby Stereo. (see "How does Dolby's matrixed sound work?") By adding an adapter (and some additional wiring) any Dolby Digital-theatre could be easily upgraded.
In the press release that announced the system it stated that "Star Wars: Episode I - The Phantom Menace" would be the first to feature a Surround EX soundtrack and the hype surrounding the film made sure the system was a success as many exhibitors wanted to upgrade their installations. Dolby Digital Surround EX soundtracks are usually found only on big budget action packed movies, where sound effects an important part of the experience are.

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DTS Digital Sound & DTS-ES :
Under Construction !!

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SDDS, short for Sony Dynamic Digital Sound, is a digital sound-on-film system capable of harbouring preview SDDS print soundtracks of up to 8 discrete channels. The digital track is locate outside the sprockets on either side of the 35mm print. A Dolby Stereo SR-compatible analog soundtrack is available in case the digital system fails.
The SDDS soundtrack is treated with the ATRAC (Audio Transform Acoustic Coding) lossy encoding algorithm, originally developed for MiniDisc which has a 5:1 compression ratio.
Because the soundtrack is located on the edges of a film it is more susceptible to scratches and wear. Several measures are taken to cope with the problems. First, the soundtrack is recorded on the cyan layer of the film, which is 3 layers down from the surface. All data is stored redundant on both sides so that when the data is corrupted on one side, the data on the other side is processed. A 17 frame offset in recording time makes sure that, when the film breaks, no data is lost. The ATRAC also provides error correction and if everything else fails there's still the analog stereo track.
The system is able to reproduce sound-mixes with 7.1, 5.1 or 4.0 discrete channels. The 7.1 setup has 5 preview SDDS 7.1 layout screen channels (Left, Left Center, Center, Right Center and Right), 2 surround channels and a subwoofer channel. The 5.1 setup is the present standard for digital formats with 3 screen channels, 2 surround channels and a LFE (Low Frequency Effects) channel. 4.0 is the discrete version of the matrixed Dolby Stereo format and its compatibles with 3 screen channels and mono surrounds. Exhibitors can choose which of the 3 types they want to install. If the soundtrack is a 7.1 mix and only a 5.1 or 4.0 system is installed, the processor mixes the 2 extra channels (Left & Right Center) into the 3 available ones. When a 8 channel system is installed but only a 5.1 or 4.0 mix is included, the processor distributes the 3 screen channels over the available 5.
SDDS premiered in 1994 with the film "Last Action Hero". Although the system can handle 7.1 mixes most releases are done in the standard 5.1 format. A SDDS-system is more expensive to install than a DTS or a Dolby Digital one and therefore it has worldwide a lower screen penetration than the competing formats. The format will stick arround, though, as most major films feature soundmixes in all 3 dominating digital formats and all releases from the Columbia Picture Studios have at least a SDDS mix, as Columbia is a division of Sony.

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