Sony Dynamic Digital Sound
Layout and function
SDDS has a maximum of eight different channels, five of them in the front, two on the sides and one LFE (Low Frequency Effects, Subwoofer ) channel for special low-frequency sound effects below 120 Hz . All SDDS processors are flexible in the number of channels and can be universally installed from four to eight channels in different variants. The SDDS processor distributes the non-existent channels to the existing loudspeakers (in practice this is usually downscaling 8-channel films to an existing 5.1 system).
SDDS was first shown on June 17, 1993 in four cinemas in Los Angeles and New York with the film Last Action Hero . The first German SDDS film was Wolf - Das Tier im Manne . Since no copier in Germany could copy SDDS in the beginning, the few German SDDS copies were imported from the USA. The remaining German copies only had a Dolby SR optical sound track . A short SDDS soundtrailer was pre-copied directly in front of many of the SDDS copies of that time. However, this meant that it also ran in cinemas with sound systems without SDDS, since after the first showing no attention was paid to which cinema received a copy with SDDS sound (SDDS copies also have the Dolby SR standard in addition to SDDS sound -Light tone and are therefore compatible with all analog cinema sound systems). This was later abandoned and it was left to the cinemas equipped with SDDS decoders to put an SDDS trailer in front of the film in order to draw the audience's attention to the SDDS sound.
The sound data in SDDS into two optical tracks left and right outside of the film perforation is stored and by means of special reading device having two CCD - cameras read out. The proprietary ATRAC method ( Adaptive Transform Acoustic Coding ) is used for compression and coding . ATRAC 2 decoder ICs are used in all processors, regardless of whether they are first generation (DFP-D2000) or second generation (DFP-D3000, DFP-D2500). There are four backup channels in addition to the eight audio channels. Four main and two backup channels are stored on each side of the film (see error correction).
SDDS can be retrofitted to all common 35 mm projectors , but the duplication of films with SDDS soundtracks is comparatively complex, since the fine structures of the SDDS soundtracks require great care: In theory, copies should be made at half the playback speed, which is normal was (and is), however, so far a multiple.
Like its competitors Dolby Digital and DTS, SDDS is now available in almost all current Hollywood films. SDDS is relatively seldom installed in the cinema, as the system can only play its essential advantage, the five front channels, on very large screens, as they are usually only available in a few halls with more than 600 seats in large cities. Many movies also only have 5.1 SDDS film sound or a sound that is automatically mixed in from the other front channels for the two additional front channels. Investing in a third system in addition to Dolby Digital and DTS is therefore not worthwhile for most cinema operators.
Another special feature of SDDS is the error correction. In addition to the normal procedure for correcting errors in the event of dust and scratches on the film copy, which is also common with Dolby Digital, SDDS offers the "DCM" (digital concealment mode) - a digital backup. The system stores a total of twelve fully-fledged audio channels, regardless of whether it is the subwoofer, a normal or a backup channel. The data is distributed on the two sound tracks of the 35 mm film copy as follows:
on the side of the analog sound track ("S-Side" - Sound-Side):
- Subwoofer (SW)
- Center right (RC)
- Right (R)
- Surround right (SR)
- Backup Center (C ')
- Backup left (Lmix)
on the picture side ("P-Side"):
- Center (C)
- Center left (LC)
- Left (L)
- Surround left (SL)
- Backup subwoofer (SW ')
- Backup right (Rmix)
Both sound tracks are copied on the film offset by 17.8 frames and are synchronized to the image by delays in the SDDS processor. As a result, it is very unlikely that the data belonging to one another will be damaged at the same time and thus unreadable (a typical damage could be a splice in the film copy). If the SDDS processor is not able to correct the damaged data using the normal error correction, it uses the data on the opposite side (which is not located at the damaged film location due to the 17.8-frame offset). There are direct copies of the center and subwoofer as a backup, the remaining channels are mixed together - separated to the right and left (Lmix is a mixture of left, center left, surround left). Due to this fact it can happen that if a helicopter flies in the surround on the standard sound track, but there is silence on the other channels, this helicopter can be heard on all channels on the damaged side. In order to prevent this, information for the decoder is stored on each sound track, indicating how loud the mix should be played on the respective channels in a backup case. The helicopter can still be heard on all channels on one side, but only in surround at the actual volume. Dialog in the center and deep bass information in the subwoofer remain completely untouched. So the short (for the duration of a splice, two film frames at 24 frames per second) fallback to a backup track remains inaudible in most cases.
If a piece of film longer than 17.8 frames is damaged in such a way that neither conventional error corrections nor the digital backup methods help, then - in the case of a film copy with all sound formats - a fallback to DTS and Dolby Digital and only if none of them three digital systems run without errors, a fallback to the analog optical sound track (mostly Dolby SR).
- Digital Theater Systems (DTS)
- Thomas Görne: Sound engineering. Fachbuchverlag Leipzig in Carl Hanser Verlag, Munich et al. 2006, ISBN 3-446-40198-9 .
- Hubert Henle: The recording studio manual. Practical introduction to professional recording technology. 5th, completely revised edition. Carstensen, Munich 2001, ISBN 3-910098-19-3 .