Dolby TrueHD
Encyclopedia
Dolby Laboratories
Dolby Laboratories, Inc. , often shortened to Dolby Labs, is an American company specializing in audio noise reduction and audio encoding/compression.-History:...
which is intended primarily for high-definition home-entertainment equipment such as Blu-ray Disc
Blu-ray Disc
Blu-ray Disc is an optical disc storage medium designed to supersede the DVD format. The plastic disc is 120 mm in diameter and 1.2 mm thick, the same size as DVDs and CDs. Blu-ray Discs contain 25 GB per layer, with dual layer discs being the norm for feature-length video discs...
and HD DVD
HD DVD
HD DVD is a discontinued high-density optical disc format for storing data and high-definition video.Supported principally by Toshiba, HD DVD was envisioned to be the successor to the standard DVD format...
. It is the successor to the AC-3 Dolby Digital
Dolby Digital
Dolby Digital is the name for audio compression technologies developed by Dolby Laboratories. It was originally called Dolby Stereo Digital until 1994. Except for Dolby TrueHD, the audio compression is lossy. The first use of Dolby Digital was to provide digital sound in cinemas from 35mm film prints...
surround sound codec which was used as the audio standard for DVDs. In this application, Dolby TrueHD competes with DTS-HD Master Audio
DTS-HD Master Audio
DTS-HD Master Audio is a lossless audio codec created by Digital Theater System. It was previously known as DTS++. It is an extension of DTS which, when played back on devices which do not support the Master Audio or High Resolution extension, degrades to a "core" track which is lossy. DTS-HD...
, another lossless codec from DTS
Digital Theater System
DTS is a series of multichannel audio technologies owned by DTS, Inc. , an American company specializing in digital surround sound formats used for both commercial/theatrical and consumer grade applications...
.
Dolby TrueHD uses Meridian Lossless Packing
Meridian Lossless Packing
Meridian Lossless Packing, also known as Packed PCM , is a proprietary lossless compression technique for compressing PCM audio data developed by Meridian Audio, Ltd. MLP is the standard lossless compression method for DVD-Audio content and typically provides about 1.5:1 compression on most music...
(MLP) as its mathematical basis for compressing audio samples. MLP was used on the earlier DVD-Audio
DVD-Audio
DVD-Audio is a digital format for delivering high-fidelity audio content on a DVD. DVD-Audio is not intended to be a video delivery format and is not the same as video DVDs containing concert films or music videos....
format, but details of Dolby TrueHD and DVD-Audio differ substantially. A Dolby TrueHD bitstream can carry up to 14 discrete sound channels. Sample depths up to 24 bits/sample and audio sample rates up to 192 kHz are supported. Like the more common legacy codec Dolby Digital
Dolby Digital
Dolby Digital is the name for audio compression technologies developed by Dolby Laboratories. It was originally called Dolby Stereo Digital until 1994. Except for Dolby TrueHD, the audio compression is lossy. The first use of Dolby Digital was to provide digital sound in cinemas from 35mm film prints...
, Dolby TrueHD bitstream
Bitstream
A bitstream or bit stream is a time series of bits.A bytestream is a series of bytes, typically of 8 bits each, and can be regarded as a special case of a bitstream....
s carry program metadata
Metadata
The term metadata is an ambiguous term which is used for two fundamentally different concepts . Although the expression "data about data" is often used, it does not apply to both in the same way. Structural metadata, the design and specification of data structures, cannot be about data, because at...
. Metadata
Metadata
The term metadata is an ambiguous term which is used for two fundamentally different concepts . Although the expression "data about data" is often used, it does not apply to both in the same way. Structural metadata, the design and specification of data structures, cannot be about data, because at...
is separate from the coding format and compressed audio samples, but stores relevant information about the audio waveform. For example, dialog normalization
Audio normalization
Audio normalization is the application of a constant amount of gain to an audio recording in order to bring the average or peak amplitude to a target level ....
and dynamic range compression are controlled by metadata embedded in the TrueHD bitstream. TrueHD is a variable bit-rate codec.
Blu-ray Disc
In the Blu-ray specification, Dolby TrueHD is an optional codec. Dolby TrueHD audiotracks may carry up to 24 bit audio in up to 8 discrete audio channels at 96 kHz or up to 6 channels (5.1 surround) at 192 kHz. The maximum encoded bitrate is 18 Mbit/s (the same as the uncompressed rate). Since TrueHD is an optional codec, a separate (primary) AC-3 audiotrack must be present on Blu-ray discs that contain a TrueHD track.All Dolby TrueHD players are capable of downmixing
Downmixing
Downmixing is a general term used for manipulating audio where a number of distinct audio channels are mixed together to produce a lower number of channels...
the decoded Dolby TrueHD audiotrack to an arbitrary number of channels more suitable for player output. For example, all Dolby TrueHD-capable players can create a 2-channel (stereo
STEREO
STEREO is a solar observation mission. Two nearly identical spacecraft were launched into orbits that cause them to respectively pull farther ahead of and fall gradually behind the Earth...
-compatible) downmix from a 6-channel source audiotrack.
Dolby TrueHD sees its most popular usage as a high definition audio codec for Blu-ray Disc. While early Blu-ray Disc players did not support Dolby TrueHD, most current models support Dolby TrueHD, and an increasing percentage of movie releases feature a Dolby TrueHD audiotrack. However, by late 2009 and early 2010, Dolby TrueHD has been steadily losing the lossless audio market share to archrival DTS-HD Master Audio
DTS-HD Master Audio
DTS-HD Master Audio is a lossless audio codec created by Digital Theater System. It was previously known as DTS++. It is an extension of DTS which, when played back on devices which do not support the Master Audio or High Resolution extension, degrades to a "core" track which is lossy. DTS-HD...
.
HD DVD
In the HD DVD format, Dolby TrueHD was a mandatory codec. The HD DVD specification permitted the sole (primary) audiotrack of a movie to be encoded in Dolby TrueHD, and the specification requires support for up to 2 channel (stereo) decoding. In practice all HD DVD players decoded multichannel (5.1) programming, and of the few HD DVD movies to be encoded with Dolby TrueHD audiotracks, all were multichannel.The Phantom of the Opera
The Phantom of the Opera (2004 film)
The Phantom of the Opera is a 2004 film adaptation of Andrew Lloyd Webber's 1986 musical of the same name, which in turn was based on the French novel Le Fantôme de l'Opéra by Gaston Leroux....
, released April 18, 2006 on HD DVD
HD DVD
HD DVD is a discontinued high-density optical disc format for storing data and high-definition video.Supported principally by Toshiba, HD DVD was envisioned to be the successor to the standard DVD format...
, was the first movie to offer a Dolby TrueHD soundtrack.
Transport
Dolby TrueHD may be transported to AV receivers in 5.15.1 surround sound
5.1 is the common name for six channel surround sound multichannel audio systems. 5.1 is now the most commonly used layout in both commercial cinemas and home theaters. It uses five full bandwidth channels and one low frequency enhancement channel . Dolby Digital, Dolby Pro Logic II, DTS, and...
or 7.1 channels, at lossless quality, in one of three ways depending on player and/or receiver support:
- Over 6 or 8 RCA connectorRCA connectorAn RCA connector, sometimes called a phono connector or cinch connector, is a type of electrical connector commonly used to carry audio and video signals...
s as analog audio, using the player's internal decoder and digital-to-analog converterDigital-to-analog converterIn electronics, a digital-to-analog converter is a device that converts a digital code to an analog signal . An analog-to-digital converter performs the reverse operation...
(DAC). - Over HDMIHigh-Definition Multimedia InterfaceHDMI is a compact audio/video interface for transmitting uncompressed digital data. It is a digital alternative to consumer analog standards, such as radio frequency coaxial cable, composite video, S-Video, SCART, component video, D-Terminal, or VGA...
1.1 (or higher) connections as 6 or 8-channel Linear PCM, using the player's decoder and the AV receiver's DAC. - Over HDMI 1.3 (or higher) connections as the original TrueHD bitstream, with decoding and DAC both done by the AV receiver.