Dolby Digital
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Dolby Digital is a digital audio encoding technology developed by Dolby Laboratories. It includes a series of lossy audio compression techniques, some of which are mentioned below.
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Dolby Digital
First used in movie theatres, Dolby Digital (which is the propriety name for AC-3) uses data reduction in order to compress up to 6 channels of sound into a two-channel bitstream. Denoted by 5.1, these channels include five discrete channels namely right front, centre, left front, right rear and left rear and one subwoofer channel for low frequency effects (LFE). The AC-3 (Dolby Digital) is used in a wide variety of applications including satellite broadcasting, high definition digital televisions, DVDs, cinemas and Laserdiscs.
Other names for the codec include DD (short form of Dolby Digital), Adaptive Transform Coder 3 (long form of AC-3) and some backronyms such as Audio Codec 3 and Acoustic Coder 3.
Dolby Digital EX
This is a new variation of the Dolby Digital codec which uses a process similar to the older Pro-Logic format to create a rear-centre channel in addition to the existing channels. Although it is referred to as 6.1, it cannot be considered as a true 6.1 channel codec because the 6th channel is not discrete.
Dolby Digital Live
Dolby Digital Live is a real-time encoding technology that converts any audio signal in PCs or video game consoles into a 5.1 Dolby Digital bitstream. This highly enhances the audio output and allows the user to have an exciting experience.
Dolby Digital Plus
The Dolby Digital Plus, denoted by DD-Plus, features many enhancements on the AC-3 codec including more channels (up to seven discrete channels and one LFE), higher bitrates (up to 6 Mbps) and an improved coding process so as to reduce loss of quality. It is also backward compatible with existing A/V receivers.
Applications
Dolby Digital is widely used for home entertainment and by professionals. In homes, it is used in home theatres, DVDs and digital TV. It is also widely used in computer multimedia, game consoles and in automobiles. Professional uses include its implementation in motion pictures (cinemas), DVD authoring and mastering, game development, integrated circuits and software.
A new lossless codec, Dolby TrueHD, is set to be the next generation format. Featuring a bitrate of up to 18 Mbps and eight channels of audio, it has been selected for HD DVDs (High Definition DVDs) as the “mandatory codec” and for the Blu-ray Disc as an “optional codec”.