Dolby Stereo
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Dolby Stereo (or Dolby Analog) was the original analog optical technology developed by Dolby Laboratories for 35 mm film prints in 1976, and first used on the movie Logan's Run. [[1]] The brand of Dolby Stereo became a world leader, and synonymous with high quality sound in thousands of movie theaters across the world.
The optical soundtrack on a Dolby Stereo encoded 35mm film not only carried left and right tracks for stereophonic sound, but also, through a matrix decoding system (which had been developed for the "quadraphonic" or "quad"-sound era of the 1970's) , a third center channel, and a fourth surround channel (which is heard over speakers on the sides and rear of the theater) for ambient sound and special effects. This yielded a total of four sound channels, in the physical track space previously allocated for just one mono optical channel, although magnetic striped film, the standard for stereophonic sound, existed in both 35mm and 70mm previously as early as 1953. Dolby also incorporated its A-Type noise reduction into the Dolby Stereo process. The original Dolby Stereo was first used on the 1975 Ken Russell film Lisztomania, in a 3-channel LCR configuration. The success of 1977's Star Wars, which used the four channel system to great effect, did much to encourage movie theaters to convert to the 4-channel LCRS speaker configuration. A key feature of this system was its backward-compatibility: the same print could play anywhere, from an older drive-in theater with mono sound to a cinema which had upgraded its system with a Dolby Stereo processor. Thus, there was no need (nor expense) in carrying a double inventory of prints for distribution.
By 1984, Dolby Stereo had a competitor. Ultra Stereo Labs had introduced a comparable stereo optical sound system, Ultra Stereo. Its cinema processor introduced improvements in matrix decoding, with greater channel separation. A balancing circuit was also included which compensated for film weave and some of the imbalances between the left and right sound tracks which had previously resulted in voice leakage into the surround channel. The Ultra Stereo sound system won a 1984 Technical Achievement Award from the Academy of Motion Picture Arts and Sciences.[1]
Dolby Stereo was displaced in 35 mm motion picture exhibition by the Dolby SR format in the mid-1980s. Dolby SR is still included on all theatrical release prints encoded with Dolby Digital, as the default track, if something goes wrong with decoding the digital track. Also the Dolby SR track is used in theaters not equipped for Dolby Digital playback.
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[edit] Dolby Surround
Dolby Surround' was the earliest consumer version of Dolby's multichannel analog film sound format Dolby Stereo.
When a Dolby Surround soundtrack is produced, four channels of audio information—left, center, right, and mono surround—are matrix-encoded onto two audio tracks. The stereo information is then carried on stereo sources such as videotapes, laserdiscs and television broadcasts from which the surround information can be decoded by a processor to recreate the original four-channel surround sound. Without the decoder, the information still plays in standard stereo or monaural. The Dolby Surround decoding technology was updated during the 1980s and re-named Dolby Pro Logic. The terms Dolby Surround and LtRt are used to describe soundtracks that are matrix-encoded using this technique.
| Dolby Surround Mixer | Left | Right | Center | Surround |
|---|---|---|---|---|
| Left Total | 1 | 0 |  |
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| Right Total | 0 | 1 | |
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j = +90° phase-shift, k = -90° phase-shift
[edit] Dolby Pro Logic
Dolby Pro-Logic is the marketing name for the consumer implementation of this audio format; the term is not applicable to cinema.
[edit] Dolby Stereo 70 mm Six Track
Dolby Stereo 70 mm Six Track refers to a different 6-channel analog magnetic recording system developed for 70 mm prints in 1976. It adapted the original Todd-AO system of 5 front channels and one surround by adding Dolby A noise reduction and replacing the extra left and right channels with twin LFE channels. The system was later modified to use Dolby SR noise reduction and split surrounds, giving the modern 5.1 channel allocation retained today by Dolby Digital.
[edit] References
- ^ [http://www.uslinc.com/article-ultra_sharp.html Film Journal International August, 1999, page 34.]
[edit] External links
- Dolby official site
