'Sony Dynamic Digital Sound' (SDDS) is a cinema sound system developed by Sony. Digital sound information is recorded on both outer edges of the 35 mm film release print. The system supports up to 8 independent channels of sound: 5 front channels, 2 surround channels and a sub-bass channel. Only Cinerama and Cinemiracle have used as many sound tracks. This arrangement is similar to 70 mm magnetic sound formats – and is useful mainly for very large cinema screens. Most cinemas are capable of four- to six-track stereophonic sound, and it may sometimes be downmixed.
Although SDDS is technically supported by the DVD specifications, very few titles include SDDS audio (Sin City special edition is one), and many (particularly older) surround sound receivers are incapable of decoding SDDS audio.
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.
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