AC3 Format

Dolby Digital includes several similar technologies, which include Dolby Digital, Dolby Digital EX, Dolby Digital Live, Dolby Digital Surround EX, Dolby Digital Plus, and Dolby TrueHD.


[edit] Dolby Digital

Dolby Digital logo that is sometimes shown at the beginning of broadcasts, feature films, and gamesDolby Digital, or AC-3, is the common version containing up to six discrete channels of sound. The most elaborate mode in common usage involves five channels for normal-range speakers (20 Hz – 20,000 Hz) (right front, center, left front, right rear and left rear) and one channel (20 Hz – 120 Hz allotted audio) for the subwoofer driven low-frequency effects. Mono and stereo modes are also supported. AC-3 supports audio sample-rates up to 48 kHz. Batman Returns was the first film to use Dolby Digital technology when it premiered in theaters in Summer 1992. The Laserdisc version of Clear and Present Danger featured the first Home theater Dolby Digital mix in 1995.

This codec has several aliases, which are different names for the same codec:

Dolby Digital (promotional name, not accepted by the ATSC)
DD (an abbreviation of above, often combined with channel count: DD 5.1)
Dolby Surround AC-3 Digital (second promotional name, as seen on early film releases and on home audio equipment until about 1995/1996)
Dolby Stereo Digital (first promotional name, as seen on early releases, also seen on True Lies LaserDisc)
Dolby SR-Digital (when the recording incorporates a Dolby SR-format recording for compatibility)
SR-D (an abbreviation of above)
Audio Coding 3 (relates to the bitstream format of Dolby Digital)
AC-3 (an abbreviation of above)
Audio Codec 3, Advanced Codec 3, Acoustic Coder 3 (These are backronyms. However, Adaptive Transform Acoustic Coding 3, or ATRAC3, is a separate format developed by Sony)
ATSC A/52 (name of the standard, current version is A/52 Rev. B)

[edit] Dolby Digital EX
Dolby Digital EX is similar in practice to Dolby's earlier Pro-Logic format, which utilized matrix technology to add a center channel and single rear surround channel to stereo soundtracks. EX adds an extension to the standard 5.1 channel Dolby Digital codec in the form of matrixed rear channels, creating 6.1 or 7.1 channel output. However, the format is not considered a true 6.1 or 7.1 channel codec because it lacks the capability to support a discrete 6th channel unlike the competing DTS-ES codec.


[edit] Dolby Digital Surround EX
The Cinema Version of "Dolby Digital EX" is called Dolby Digital Surround Ex and works the same way. Dolby Digital Surround EX was co-developed by Dolby and Lucasfilm THX in time for the release in May 1999 of Star Wars Episode I: The Phantom Menace. It provides an economical and backwards-compatible means for 5.1 soundtracks to carry a sixth, center back surround channel for improved localization of effects. The extra surround channel is matrix encoded onto the discrete Left Surround and Right Surround channels of the 5.1 mix, much like the front center channel on Dolby Surround encoded stereo soundtracks. The result can be played without loss of information on standard 5.1 systems, or played in 6.1 or 7.1 on systems equipped with Surround EX decoding and additional speakers. Dolby Digital Surround EX has since been used for the Star Wars prequels on the DVD versions and also the remastered original Star Wars trilogy. A number of DVDs have Dolby Digital Surround EX audio option.


[edit] Dolby Digital Live
Dolby Digital Live (DDL) is a real-time hardware encoding technology for interactive media such as video games. It converts any audio signals on a PC or game console into a 5.1-channel Dolby Digital format and transports it via a single S/PDIF cable.[1] A similar technology known as DTS Connect is available from competitor DTS.

Dolby Digital Live is currently available in sound cards from manufacturers such as Creative Labs, Diamond Multimedia, TerraTec, Turtle Beach,[2] HT OMEGA SYSTEM,[3] Auzentech[4] and Asus[5] using C-Media chipsets. The SoundStorm, used for the Xbox game console and certain nForce2-based PCs, used an early form of this technology.

DDL is also available on motherboards with codecs such as Realtek's ALC882D,[6] ALC888DD and ALC888H.

DDL is also supported by all Creative X-Fi based sound cards (except the Xtreme Audio which is not capable of DDL in hardware), but was intentionally disabled in the original drivers by Creative on all but the Auzentech Prelude. A programmer named Daniel Kawakami had re-enabled this feature and fixed other bugs in the Windows drivers through a series of modified drivers that he made publicly available. Creative Labs had alleged that Daniel had violated their intellectual property and demanded he cease distributing his modified drivers.[7][8]

In 2008 Creative released the X-Fi Titanium series of sound cards which fully support Dolby Digital Live. In addition, in September 2008 Creative began selling the "Dolby Digital Live" and "DTS Connect" packs which enables Dolby Digital Live on Creative's X-Fi series of sound cards. It can be purchased and downloaded from Creative.[9]

An important benefit of this technology is that it enables the use of digital multichannel sound with consumer sound cards, which are otherwise limited to PCM stereo or multichannel analog.


[edit] Dolby Digital Plus
Main article: Dolby Digital Plus
E-AC-3, more commonly known as Dolby Digital Plus, is an enhanced coding system based on the AC-3 codec. It offers increased bitrates (up to 6.144 Mbit/s), support for more audio channels (up to 13.1), and improved coding techniques to reduce compression artifacts. It is not backward compatible with existing AC-3 hardware, though E-AC-3 decoders generally are capable of transcoding to AC-3 or DTS for equipment connected via S/PDIF. Only the discontinued HD DVD system directly supported E-AC-3, though Blu-ray disk offers E-AC-3 as a option to graft additional channels onto an otherwise 5.1 AC-3 stream.


[edit] Dolby TrueHD
Main article: Dolby TrueHD
Dolby TrueHD, developed by Dolby Laboratories, is an advanced lossless audio codec based on Meridian Lossless Packing. Support for the codec was mandatory for HD DVD and is optional for Blu-ray Disc hardware. TrueHD supports 24-bit, 96 kHz audio channels at up to 18 Mbit/s over 14 channels (HD DVD and Blu-ray Disc standards currently limit the maximum number of audio channels to eight). It also supports extensive metadata, including dialog normalization and Dynamic Range Control.