The technologies in brief - Dolby Digital Article from Dolby Laboratories Inc.

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Dolby Digital, sometimes known as "AC-3" for the technology on which it is based, is a perceptual coding for consumer applications that enables storing and transmitting from one to 5.1 audio channels at a low data rate. Dolby Digital audio is used for digital television, digital cable, and DBS transmissions, and for DVD and laser discs.

The Dolby Digital 5.1-channel format

A unique feature called "downmixing" makes it possible for any consumer playback system with Dolby Digital decoding, regardless of channel configuration, to play 5.1-channel Dolby Digital programs. Mono and two-channel consumer decoders automatically create mono, stereo, or Dolby Surround Lt/Rt mixes "on the fly" from multichannel programs. As a result, the same multichannel Dolby Digital bitstream can be delivered to, and satisfy, all listeners. (See: Dolby Digital Downmixing)       Supplementary information known as metadata is added during production, post-production, or transmission to identify a Dolby Digital soundtrack's production format�mono, stereo, matrixed or discrete surround�and ensure proper playback. Other metadata parameters include dialnorm, which maintains a constant dialogue-keyed playback level for all program material and sources, and dynrange, which applies a pre-determined amount of dynamic range compression when listening conditions warrant, such as late at night.

Dolby Digital Downmixing

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