What is Dolby Digital?

Dolby Laboratories, founded in 1965, has been arguably the most influential company in the sound industry since its inception. Most people are familiar with the Dolby Logo, stemming back to when analog cassette tapes were the standard for music listening. Although few people knew how the Dolby Noise Reduction system worked, they did know that tapes played back with Dolby technology sounded better when it was used.

Although Dolby got their start by working on noise reduction technology for analog recording, they have ended up as the dominant leader in movie sound industry. Their Dolby Stereo system, the first to provide high quality multi-channel playback in movie theaters, has no doubt revolutionized the way audiences have heard film sound since 1976's A Star is Born.


As Dolby entered the home market, their Dolby Surround technology, as well as the Pro Logic format, changed the home movie sound market dramatically. Then in 1992, Batman Returns became the first film to use Dolby's AC-3 Digital Surround format (now known as Dolby Digital). Dolby Digital was the first encoding system to allow up to 6 fully discrete channels of high quality sound information, digitally compressed to take up very little space. In fact it is so small that Dolby Digital sound information fits between the sprocket holes on the film's edge.

Dolby Digital is an encode/decode system, designed to compress lots of audio information into a very small space. Standard PCM stereo signals (the kind of data used on CD's) would take up an enourmous huge amount of bandwidth, meaning that 6 discrete sound channels of regular PCM data would take up too much space to make it useful for film, TV broadcasting, or home video. Using advanced psychoacoustic principals, specifically auditory masking, Dolby Digital can compress the same 6 discrete sound channels to just 384 thousand (kilo) bits per second. This is about one-twelfth the size of the PCM data stream. 

Though first developed for the new digital TV standard in the US, Dolby Digital has made its way into movie theaters, DVD, Blur-Ray, Digital TV, LaserDisc, video games, and more - making it the most dominant digital sound format ever created.

Learn more about Dolby Digital at the official Dolby Laboratories website.


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