Originally Posted by rbinck
Letís Talk Surround
Then in 1966 Dolby Labs came out with a breakthrough in sound processing, the Dolby A-type noise reduction system. This would finally allow the optical audio on films to carry a stereo sound track.
Dolby A is strictly a noise reduction system used for 2" analog and 1/2 track recorder/reproducers. An extremely sophisticated system which splits the signal into 4 discrete bands and uses the principles of compression and mirror expansion to reduce the noise floor of analog tape on the way up, and raises the signal (decode) on the way down thereby eliminating tape hiss. thus the mirror image double D logo which has existed for years. this is an extremely basic explanation of the workings of dolby A, which has absolutely nothing to do with encoding stereo tracks on film.
originally dolby labs had nothing to do with film and invested all of their energies into high end studio recording. some years back they made a stategic move to develop a discrete multi channel system that was code named "AC3" which stood for audio code number 3, it's developmental name. while the original dolby type "A" systems are still in use with world class recordings that you hear every day, today the name dolby has a completely different connotation and is inseparable from the film industry.