While Dolby does not feel uniquely attached to the two-track stereo optical format, it does seem to have several salient advantages when compared with some other proposals. First, the laboratory problems are greatly eased by the variable area tracks, which are no different in terms of processing from conventional optical sound-tracks. Second, two tracks are superior to three or more tracks on the film when compatibility to monaural is required. Third, two tracks will have a better signal-to-noise ratio than three or four tracks, and make for much cheaper and easier to install projector modifications and optical recorders. Finally, two tracks, and no more, minimize problems caused by printer misalignment and projector weave, and illumination non-uniformity during playback.
Two Loudspeakers or Three
While two loudspeakers (left and right)—may be sufficient for domestic music playback, and perhaps in theatres that are long and very narrow, in wide theatres a member of the audience sitting near the front and on the side of the theatre has the disturbing effect of a center front signal appearing to come from the nearer loudspeaker, a particularly bothersome effect when the sound should be coming from a center screen actor. Dolby developed a logic circuit for use during playback of the two-track film. The circuit constantly analyzes the differences between the left and right track signals and redevelops a center signal, which is sent to a center screen loudspeaker. In this way, three loudspeakers are in use, L, C and R, and the resultant sound is normally indistinguishable from a conventional three-track signal intended for magnetic stripe three track discrete playback.
Several films have now been released with Dolby encoded twin-track SVA (stereophonic variable area) sound tracks. In Europe, Tommy was released this way, and in the U.SA. recently Mr. Billion and A Star is Born.
Stereo Optical Surround Track
In addition to a large number of technical improvements to the stereo optical format over the last few years, Dolby has recently developed a method of adding surround information to the optical track. In order not to reduce the advantage of having only two tracks on the film, the surround information is Sansui matrix (OS) endoded onto the two-track signal; new techniques are used along with the matrix circuitry to reduce any residual cross-talk signals turning up on the surround speakers during what should be front-only signal conditions.
Dolby and Star Wars
Gary Kurtz and George Lucas, the producer and director of Star Wars, approached Dolby Laboratories in 1975 to discuss the sound track of the film. They felt that a film of this type warranted a sound track of a quality better than could be achieved from using conventional techniques, and from Dolby's point of view the subject matter would allow them to show their wares in a way more demonstrative than was common. It was decided early on by all involved that magnetic striping of 35mm release prints should be avoided, because of the quality problems previously mentioned. Dolby-encoded stereo optical with a surround track seemed ideally suited for the 35mm prints, and Dolby encoding would also be applied to the 70mm releases, which would also employ a new technique Dolby had developed for an extended base response using loud-speakers 2 and 4 (with five speakers behind the screen).
Many changes in technique are called for during the preparation of the sound track, if the full advantages of the better release prints are to be fully utilized. These started right back at the location stages of sound recording when Dolby engineers met with the location and floor mixer in London prior to the commencement of shooting. Wherever possible, the quarter-inch location and floor tape were Dolby encoded, but more importantly, the minimum possible use of limiting was made, and no equalization was allowed. Conventionally, the sound recordist, knowing that his recordings will ultimately be played back on a theatre system with a poor high-frequency characteristic, may boost the highs on the tape. While this may make for better intelligibility on the dailies, it leads to much higher distortion, and would obviously sound excessively bright when played back in a wide-range Dolby-equipped playback situation.
All dailies (35mm transfers), effects, ADR and Foley were also Dolby-encoded. Looping and premixing were carried out in London at De Lane Lea and in Hollywood at Producers Sound Services. The Burbank Studios, Goldwyn and Glen Glenn. The music was recorded at Anvil Studios in England.
Final mixing took place at Goldwyn Studios in April of this year. Because of the dual release requirements, six-track 70mm and stereo optical, a four-track master was prepared, carrying left, center, right and surround information. At the end of the mix, the four-track was used to prepare a two-track running master for stereo optical use, and the same four-track was also taken to Todd-AO where it was used to make a six-track running master for 70mm. Optical printing was carried out at Deluxe Labs, and the 70mm recording at Todd-AO.
More than 50% of the first-wave release theatres for Star Wars will be equipped with Dolby theatre playback packages, containing the necessary noise-reduction decoders and equalizers that exactly tailor the loud-speaker responses to match those of the dubbing theatre where the film was mixed. In this way, for the first time ever, the sound heard in the theatre should to all intents be identical to that heard by the director during the mix.
The Dolby participation on Star Wars marks another step toward bringing motion picture sound reproduction and theatre playback to the high quality level that the audience expects and appreciates.
