Sony Dynamic Digital Sound, as known as SDDS, is a digital film sound format comprising the SDDS soundtrack, optically printed on both edges of 35mm film; and SDDS playback hardware.

The Format

Sony designed SDDS exclusively for motion picture theaters; there is no consumer equivalent. SDDS is the only motion picture sound format to offer up to 8 channels of digitally encoded sound.


The soundtrack consists of an array of microscopic dots (or pixels) much like those recorded on a CD. With SDDS, both edges are used to provide two continuous streams of data interleaved using a cross-redundant error correction technique to further prevent drop-outs from film damage or scratches.


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. Special integrated circuits—called 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.


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.

How the soundtrack is Created

Once filming is complete, the project enters the post-production phase. The process of creating the SDDS soundtrack often begins during the editorial phase where sound editors create a unique "sound design" that matches the picture and conveys the mood and feelings of the director. With SDDS, the availability of two additional behind-the-screen channels gives the editors a chance to be more flexible and creative with the soundtrack.

Re-recording facility

The sound mixing professionals take the elements created by the sound editors and blend the dialog, music and effects together to create a pleasing and balanced soundtrack. The mix happens at the re-recording facility—essentially a full scale cinema that contains the mixing console and recording equipment. The re-recording facility allows the mixers and directors to make creative decisions in an acoustical environment that closely matches where the audience will ultimately hear the film.

Optical transfer facility

Once the mixing is complete, an optical transfer facility takes the master recording and creates the 35mm SDDS sound negative used for mass production of release prints. The 35mm negative is created using a special digital recorder that is added to the industry standard Westrex or Albrecht analog stereo sound recorder. The SDDS soundtrack is recorded at the same time as the analog soundtrack.


Once the sound negative has been made, it is sent to the laboratory to be combined with the picture negative. The color picture negative and the separate sound negative are run through an optical "printer" to marry the digital and analog soundtracks onto a third 35mm film strip with the picture. This creates the release print which is distributed for exhibition in theaters.

Current Status

Currently Sony has stopped supporting the SDDS system. A majority of release prints 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.

From its inception, SDDS had the least penetration of theatre that did install digital sound. The reasons for this are complex, but one of the primary causes is that it was the most expensive of the three contenders. Because Sony was the parent company which owned the Sony Theatre chain and Columbia Pictures, it was able use SDDS in its own theatres and on quite a number of titles through its film releasing arm. This gave SDDS a much needed, albeit artificial, kick-start. More than likely it would have garnered even less penetration had Sony not controlled both a theatre chain and a film studio.

In reality, all three systems offer the same high quality, high definition sound which, from the perspective of the theatre-goer, is indistinguishable one from the other, no matter which digital system is used in playback. As for SDDS's much touted eight track playback capability as opposed to only six channels of the other systems: although eight channels are capable with SDDS, in practice this capability is rarely employed in the mix or in the theatre systems because it requires that a separate eight channel sound mix be created in the post production stage in addition to the six channel mix that is needed for SRD and DTS. It also requires additional speakers and amplifiers in the theatre. Many theatres that do have SDDS playback installed, do so without adding the extra expense of installing the equipment needed for the additional two channels.

Whereas SDDS is a well-designed, well executed system, its considerably greater expense was not seen by theatre owners as translating into an increase in ticket sales and so it has not emerged as the dominant of the three systems. Subsequently Sony's lack of technical support in recent years for the system has exacerbated SDDS's decline.

External links

* [ Sony Dynamic Digital Sound]

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