Dolby Digital

In 1992, Dolby labs launched its revolutionary audio standard Dolby Digital to theaters at the premier of Batman Returns. The new format they called AC-3 at the time wasn't yet available to the home market.

Dolby Digital at a glance:

• Dolby Digital is the most popular audio format for DVD today.
• Consists of five full frequency channels and one LFE for 5.1
• Fully digital audio format carries the information of 5 RCA jacks on 1 digital cable.
• Requires all playback hardware to be compatible to properly decode.

Dolby Digital 5.1 consists of six discreet channels of sound:

• 2 front speakers for sound effects to the left and right of the screen
• a center for all the sounds emitting from on screen including dialogue
• 2 full-frequency rear channels for sounds behind and to each side of the audience
• and a low-frequency effects channel that requires a subwoofer but only uses one-tenth the bandwidth of the other channels, so it's the 0.1 channel.

In 1996, the first DVD players hit the market and Dolby Digital quickly became the de-facto audio standard for the new media. Today, nearly every DVD has a Dolby Digital soundtrack.

The presence of a Dolby Digital surround track doesn't necessarily mean all six channels will be used, however. Older films whose soundtracks are converted from their original stereo or mono analogue soundtracks are cheaply digitized directly to Dolby Digital with almost no discernable change.

Only if the DVD release stipulates that a "remastered" version of the soundtrack is available will Dolby Digital use the surround or LFE channels.

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