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optical-sound

Sony Dynamic Digital Sound

SDDS stands for Sony Dynamic Digital Sound, which 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.

SDDS is not currently available on any home format.

History

SDDS was developed for Sony under contract with Semetex Corp., located in Torrance, California. 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 have been equipped to with SDDS.

The Code name for the SDDS project was "Green Lantern", taken from a 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.

The SDDS Chief Architect was Jaye Waas and the Chief Optical Engineer was Mark Waring, both employed by Semetex.

The SDDS development took just 11 months from concept to working sound camera, but at the cost of working 16 hours a day, 7 days a week.

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, mostly because most mixing studios are geared towards producing 5.1 mixes rather than 7.1 mixes. Since the additional sound equipment required for 8 channel SDDS makes it more expensive to install, it tends to be installed only in larger venues.

SDDS was consistently the least popular of the three formats, and Sony Cinema Products finally, closed shop in 2002. SDDS is still supported by most of the major studios, but is not frequently installed in new cinemas anymore. However it is still a very active format with usage in over 150 new features in 2005 and well over 100 announced for 2006. Of these, only 5 were in 8-channels for 2005, and 4 for 2006.

The bulk of major cinema release prints produced in Western countries now simultaneously carry SDDS, DTS, and Dolby Digital data (or "tracks") as well as the traditional two-channel optical sound track. The optical track is required on every print, both because not all cinemas are yet equipped for digital sound, and as a backup in case the digital information fails.

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 (Dolby Digital or DTS) if available, or (most likely) to analog sound. These drop-outs are audible to most audiences as a change in volume level and a slight loss of fidelity and low-end, although it is more difficult to tell in a properly calibrated auditorium.

SDDS lags behind both Dolby Digital and DTS in deployment due to its late arrival, combined with its reliability issues and lack of new equipment. Dolby Digital is included on nearly all releases, and is often the only track on independent or low-budget films. The DTS track is usually included on major releases, although playback requires matching CD-ROMs which are not always supplied.

See also List of 8 channel SDDS films.

Technical

Original format used: 8 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. 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. 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 security the two sides of the film are separated by 17 frames - so a single splice or series of missing frames will not result in a total loss of data.

References

External links

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