Dolby Digital has similar technologies, included in Dolby Digital EX, Dolby Digital Live, Dolby Digital Plus, Dolby Digital Surround EX, Dolby Digital Recording, Dolby Digital Cinema, Dolby Digital Stereo Creator and Dolby Digital 5.1 Creator.
Dolby AC-3 Dolby AC-3 (a
backronym for Audio Codec 3, Advanced Codec 3, or Acoustic Coder 3), also known as
ATSC A/52 (name of the standard) or simply
Dolby Digital (
DD), is the common version containing up to six discrete channels of sound. Before 1996 it was marketed as
Dolby Surround AC-3,
Dolby Stereo Digital, and
Dolby SRD. The most elaborate mode of this codec in common use involves five channels for normal-range speakers () (right, center, left, right surround, left surround) and one channel ( 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. In 1991, a limited experimental release of
Star Trek VI: The Undiscovered Country in Dolby Digital played in 3 US theatres. In 1995, meanwhile in Japan,
Whisper of the Heart was the first Japanese film to be presented in Dolby Digital. In 1995, the
LaserDisc version of
Clear and Present Danger featured the first
home theater Dolby Digital mix, quickly followed by
True Lies,
Stargate,
Forrest Gump, and
Interview with the Vampire among others.
Dolby Digital Surround EX Dolby Digital Surround EX (sometimes shortened to Dolby Digital EX) is similar to Dolby's earlier
Pro Logic format, which utilized
matrix technology to add a
center surround 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. 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 Pro Logic 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 with Surround EX decoding and added speakers. A number of DVDs have a Dolby Digital Surround EX audio option. The theater version of
Dolby Digital Surround EX was introduced in 1999, Dolby Laboratories collaborated with
THX, a division of
Lucasfilm Ltd., to create the new sound system
Dolby Digital Surround EX™ for the release of
Star Wars: Episode I – The Phantom Menace. Dolby Digital Surround EX has since been used on the DVD releases of the
Star Wars prequel and original trilogies. A similar technology known as
DTS Connect is available from competitor
DTS. 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 digital
PCM stereo or analog multichannel sound because S/PDIF over RCA, BNC, and TOSLINK can only support two-channel PCM, Dolby Digital multichannel audio, and DTS multichannel audio.
HDMI was later introduced, and it can carry uncompressed multichannel PCM, lossless compressed multichannel audio, and lossy compressed digital audio. However, Dolby Digital Live is still useful with HDMI to allow transport of multichannel audio over HDMI to devices that are unable to handle uncompressed multichannel PCM. Dolby Digital Live is available in sound cards using various manufacturers' audio chipsets. The
SoundStorm, used for the
Xbox game console and certain
nForce2 motherboards, used an early form of this technology. DDL is available on motherboards with codecs such as
Realtek's ALC882D, ALC888DD and ALC888H. Other examples include some
C-Media PCI sound cards and Creative Labs' X-Fi and Z series sound cards, whose drivers have enabled support for DDL. NVIDIA later decided to drop DDL support in their motherboards due to the cost of involved royalties, leaving an empty space in this regard in the sound cards market. Then in June 2005 came
Auzentech, which with its X-Mystique PCI card, provided the first consumer sound card with Dolby Digital Live support. Initially, no Creative X-Fi-based sound cards supported DDL (2005~2007) but a collaboration of Creative and
Auzentech resulted in the development of the Auzentech Prelude, the first X-Fi card to support DDL. Originally planned to extend DDL support to all X-Fi-based sound cards (except the 'Xtreme Audio' line which is incapable of DDL hardware implementation), the plan was dropped because Dolby licensing would have required a royalty payment for all X-Fi cards and, problematically, those already sold. In 2008, Creative released the X-Fi Titanium series of sound cards which fully supports Dolby Digital Live while leaving all PCI versions of Creative X-Fi still lacking support for DDL. Since September 2008, all Creative X-Fi-based sound cards support DDL (except the 'Xtreme Audio' and its derivatives such as Prodigy 7.1e, which is incapable of DDL in hardware).
X-Fi's case differs. While they forgot about the plan, programmer Daniel Kawakami made a hot issue by applying Auzentech Prelude DDL module back to Creative X-Fi cards by disguising the hardware identity as Auzentech Prelude. Creative Labs alleged Kawakami violated their intellectual property and demanded he cease distributing his modified drivers. Eventually Creative struck an agreement with Dolby Laboratories regarding the Dolby license royalty by arranging that the licensing cost be folded into the purchase price of the Creative X-Fi PCI cards rather than as a royalty paid by Creative themselves.
Dolby Digital Plus E-AC-3 (Dolby Digital Plus) is an enhanced coding system based on the AC-3
codec. It offers increased
bit rates (up to ), support for even more
audio channels (up to 15.1 discrete channels in the future), and improved coding techniques (only at low data rates) to reduce
compression artifacts, enabling lower data rates than those supported by AC-3 (e.g. 5.1-channel audio at ). It is not backward compatible with existing AC-3 hardware, though E-AC-3
codecs generally are capable of
transcoding to AC-3 for equipment connected via
S/PDIF. E-AC-3 decoders can also decode AC-3 bitstreams. The fourth generation Apple TV supports E-AC-3. The discontinued
HD DVD system directly supported E-AC-3.
Blu-ray Disc offers E-AC-3 as an option to
graft added channels onto an otherwise
5.1 AC-3 stream, as well as for delivery of secondary audio content (e.g. director's commentary) that is intended to be mixed with the primary audio soundtrack in the Blu-ray Disc player.
Dolby AC-4 Dolby AC-4 is an audio compression standard supporting multiple audio channels and/or audio objects. Support for 5.1 channel audio is mandatory and additional channels up to 7.1.4 are optional. AC-4 provides a 50% reduction in bit rate over AC-3/
Dolby Digital Plus.
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. Dolby TrueHD supports 24-bit bit depths and sample rates up to 192 kHz. Maximum bit rate is while it supports up to 16 audio channels (HD DVD and Blu-ray Disc standards currently limit the maximum number of audio channels to eight). It supports metadata, including dialog normalization and Dynamic Range Control. == Channel configurations ==