Dolby Stereo
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Dolby Stereo (or Dolby Analog) was the original analog optical technology developed by Dolby Laboratories for 35 mm prints in 1976, and first used on the movie A Star Is Born. The brand of Dolby Stereo became a world leader, and synonymous for 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, 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. 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. Dolby Stereo was displaced in 35 mm motion picture exhibition by the Dolby SR format in the mid-1980s.
| Dolby Surround Mixer | Left | Right | Center | Surround |
|---|---|---|---|---|
| Left Total | 1.000 | 0.000 | 0.707 | j0.707 |
| Right Total | 0.000 | 1.000 | 0.707 | k0.707 |
j = + 90º phase-shift , k = - 90º phase-shift
Dolby Pro-Logic is the marketing name for the consumer implementation of this audio format; the term is not applicable to cinema.
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.
