for the new CDS digital audio and data tracks. Six audio channels were implemented; Five full-bandwidth audio channels (three behind screen and two surround channels) were applied to the input of the system as linear 16-bit samples at a 44.1 kHz sample rate. Samples were data compressed into 12-bit words via Delta-Modulation, with one in every 32 samples retaining its original linear 16-bit form to provide an accurate reference every 726μm. The subwoofer (.1 Low Frequency Effects) channel did not employ Delta-Modulation. Instead the 44.1 kHz sample rate was decreased to 1378 Hz, which yielded an upper audio bandwidth of 114 Hz with anti-aliasing and anti-imaging strategies applied in the remainder of the frequency range. In addition to the six digital audio channels, three data/control channels were provided. One SMPTE time code channel and another channel for MIDI control signals offered flexibility for performing theater automation or external synchronization of equipment. The third data channel, an identification track, could be used to record a variety of user-defined parameters specific to the film (such as curtain opening/closing, seat movement or lighting effects.) In view of the fact that the CDS system was available for only two years before its complete withdrawal from the market, no use of the SMPTE time code or MIDI channels was ever implemented. Because the data rate was 5.8 million bits-per-second (5.8mbp/s), significant error detection and correction was required. A custom designed Reed-Solomon block code, was used with additional CRC characters for error correction. Interleaving of odd and even audio samples was performed to protect against burst errors. Just as in audio tape machines, transport problems with tension, guides, and supply and take-up reels could result in vertical or horizontal weave, and as bit sizes were only 14μm, precise timing and tracking was essential, thus the CDS system required installation of special projector modifications to smooth the film path travel and steady the take-up speed. It was found later, however, that modifications to the projectors were not needed and that the CDS systems sensitivity to improper film speed was due to a diode installed incorrectly in the CDS decoder module. Horizontal tracking was provided by a 76-MHz digital servo, while vertical timing was accomplished with an algorithm written into the data format itself. Rows of data were scanned horizontally, thus a self-clocking run-length-limited code was used for this error correction. A 6-to-8-bit mapping was performed upon encoding