Sony Dynamic Digital Sound
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'Sony Dynamic Digital Sound' (SDDS) is a cinema sound system developed by Sony. Compressed digital sound information is recorded on both outer edges of the 35 mm film release print. The system supports up to eight independent channels of sound: five front channels, two surround channels and a single sub-bass channel. The eight channel arrangement is similar to large format film magnetic sound formats like Cinerama and Cinemiracle. The five front channels are useful for very large cinema auditoriums where the angular distance between center and left channels may be considerable. SDDS decoders provides the ability to downmix to fewer channels if required.
Although SDDS is technically supported by the DVD specification, there are no consumer surround sound processors capable of decoding SDDS audio.[1]
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[edit] History
Although originally slated to premier with Hook, the SDDS project was delayed and instead premiered on June 17, 1993 with the Arnold Schwarzenegger film Last Action Hero. Since then, over 1,400 movies have been mixed in Sony Dynamic Digital Sound, and as of early 1999 over 6,750 movie theaters were equipped with SDDS.
The code name for the SDDS project was "Green Lantern", taken from the name of the comic book hero and the old term of "magic lantern" used to describe the original projected pictures in the late 19th century. Green came to mind because the key to imprinting the 8 micrometre data bits was to use a green laser.
Initial development efforts were conducted for Sony's Columbia Pictures Sound Department under contract with Semetex Corp. of Torrance, California. At Semetex, the SDDS Chief Architect was Jaye Waas and the Chief Optical Engineer was Mark Waring.
The Semetex prototype design actually had the 8 channels of uncompressed data placed into 3 locations: data bordering both sides of the analog sound track and additional data tracks bordering the opposite edge of the picture frame. These locations were chosen to ensure the data were not placed into the sprocket perforation area of the film to prevent the known wear and degradation that occurs in the perforation area (due to the mechanical film sprockets) from degrading the data. After Sony received the prototype they enlarged the data bits and moved the data locations; the eight digital audio channels are now recorded on (and recovered from) the edges of the film. As Sony engineers became more actively involved in the project, the design of the SDDS format evolved toward a more robust implementation, including the use of 5:1 ATRAC data compression, extensive error detection and correction, and most critically redundancy. The redundancy allows data to be recovered substantially intact even in the presence of a film splice. The data bit size on film was enlarged from 8 to 24 micrometers square, and Semetex's green laser system for the sound camera was replaced with simpler LED/fiber optic assemblies, which the change to 24 micrometers square then allowed.
The SDDS development took just 11 months from concept to working sound camera.
When it came time for deployment, since Sony also owned the Sony Theatres chain (later sold to Loews Theatres), it was able use SDDS in its own theatres. And via its highly successful Columbia/Tristar Studios arm, it was able to use SDDS as the exclusive digital soundtrack on its titles. In addition, in the early days of the "megaplex explosion", Sony struck a deal with AMC Theatres in 1994 to include SDDS in all of their new auditoriums. This gave SDDS a much needed, albeit artificial, kick-start. More than likely it would have garnered far less penetration had Sony not controlled both a theatre chain and a film studio.
SDDS was consistently the least popular of the three competing digital sound formats (the other two being Dolby Digital (aka SRD) and DTS). Along with being the most expensive to install (and the last to arrive), there were major reliability issues with SDDS. Due to their placement on the very edges of the film stock, SDDS tracks are more prone to damage than the other digital formats. As with other digital sound formats, any failure of the digital track will result in a "drop-out" to either another digital format if available, or (most likely) to analog sound. These drop-outs are audible to audiences as a change in volume level and a slight loss of fidelity and extreme high and low-end, similar to a "CD skipping", although it is more difficult to tell in a properly calibrated auditorium.
SDDS's much-touted eight track playback capability never quite caught on, as it required that a separate eight channel sound mix be created in addition to the six channel mix that is needed for SRD and DTS, an additional expense for the studios. Out of the 1,400 plus films mixed in SDDS, only 97 of them to date have been mixed to support the full 8 channels, most of them Sony (Via Sony Pictures/Columbia/Tristar) releases. Because of the added installation expense, the majority of SDDS installations are 6 channel (5.1) installations, as opposed to 8 channel (7.1) installations.
- See also List of 8 channel SDDS films.
SDDS 8-Channels; this logo is used when all 8 channels are used as opposed to the usual six.
While most major studios eventually began putting SDDS tracks on their releases (Universal exclusively supported DTS until 1998, and Paramount and Fox placed SDDS tracks on only their biggest releases until 2001-2002), most independent films only came with Dolby Digital tracks, leaving many SDDS-equipped theaters playing analog sound in otherwise state-of-the-art auditoriums. As Dolby Digital (and to a lesser degree, DTS) began to emerge as the clear winner in the digital sound battle, Sony Cinema Products quit manufacturing SDDS encoders and decoders, although it will continue supporting equipment that is still deployed in the field.[2]
Today, a majority of release prints for major studio films still are created with all three digital tracks -- Dolby Digital, DTS and Sony's SDDS (each digital track uses different film geography so all three, as well as the analog track, can coexist on one print) -- but most professionals in the industry now consider SDDS a dying system. AMC, for example, has begun to replace their SDDS equipment with Dolby Digital processors.
[edit] Technical
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- Original format used: 8 micrometre square data bits.
- Final format used: 24 micrometre square data bits.
The format carries up to 8 channels of discrete digital sound encoded using Sony's ATRAC codec with a compression ratio of about 5:1 and a sampling rate of 44.1 kHz.[3] The channels are:
- 5 screen channels
- Left
- Left center
- Center
- Right center
- Right
- 2 surround channels
- Left surround
- Right surround
- Subwoofer channel
Additionally there are 4 backup channels encoded - in case of damage to one side of the film or the other. These are:
- Center
- Subwoofer
- Left + left center
- Right + right center
This gives a total of 12 channels, for which the total bitrate of 2.2 megabits per second.[3] This is obviously more than the maximum 1.536 megabits per second DTS format bitrate, and far greater than the cinema Dolby Digital bitrate of 0.37 megabits per second.
For additional data reliability the two sides of the film are separated by 17 frames,[3] so a single splice or series of missing frames will not result in a total loss of data.
[edit] Reader
The SDDS reader is mounted on top of a 35mm projector. The film is threaded through the reader before it passes through the picture aperture. As the film runs, red LEDs are used to illuminate the SDDS soundtrack. CCDs (Charge-Coupled Devices) read the SDDS data and convert the stream of dots on the film into digital information. This information is pre-processed in the reader and passed on to the SDDS decoder.
[edit] Decoder
The SDDS decoder is installed in the sound equipment rack. The decoder receives the information from the reader and translates it into audio signals routed to the cinema's power amplifiers. The decoder is responsible for a series of processes that must be performed before the audio is recovered. Next, errors caused by scratches or damage to the film are corrected using redundant error recovery data. Since SDDS is read at the top of the projector, the data is delayed slightly to restore synchronization with the picture. And finally, adjustments in tonal balance and playback level are made to match the specific auditorium's sound system and acoustics. SDDS is designed to process sound entirely in the digital domain, bypassing any existing analog processor, preserving clarity and providing full dynamic range.
[edit] References
- ^ Many DVD 'rippers' incorrectly identify DTS tracks as SDDS, which can cause confusion.
- ^ http://www.sdds.com/PDFS/04SDDSDiscontinuationLetter.pdf
- ^ a b c "Sony Print Master Guidelines". http://www.sdds.com/pdfs/SDDSPrintMaster.PDF.
