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 35mm film release print. The system supports up to 8 independent channels of sound: 5 front channels, 2 surround channels and a sub-bass channel. This arrangement is similar to 70 mm magnetic sound formats - and is useful mainly for very large cinema screens. Smaller cinemas normally only have 3 screen channels - in which case the soundtrack is downmixed.
SDDS is not currently available on any home format.
SDDS was developed at the same time as it's key competitors Dolby Digital and DTS. SDDS was the last of the three formats to premier, on June 17, 1993 with the Arnold Schwarzenegger film Last Action Hero .
Since then over 1,355 movies have been mixed in Sony Dynamic Digital Sound, and as of early 1999 over 6,750 movie theaters have been equipped with SDDS.
Out of the 1,355 plus films mixed in SDDS, only 95 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. Also the additional sound equipment required for 8 channel SDDS makes it more expensive to install meaning that it only tends to be installed in larger venues.
- See also List of 8 channel SDDS films.
The SDDS soundtrack is actually printed on with the cyan color layer on the outside edges of the projected film just outside the sprocket holes.
The format carries up to 8 channels of discrete digital sound encoded using Sonys 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 center.
- Right center.
- 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:
- Left + left center.
- Right + right center.
This gives a total of 12 channels, for which the total datarate is 2.2 megabits per second. This is comparable to the DTS formats 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.
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