Dolby TrueHD

Dolby TrueHD is a lossless, multi-channel audio codec developed by Dolby Laboratories for home video, used principally in Blu-ray Disc and compatible hardware. Dolby TrueHD, along with Dolby Digital Plus (E-AC-3) and Dolby AC-4, is one of the intended successors to the Dolby Digital (AC-3) lossy surround format. Dolby TrueHD competes with DTS's DTS-HD Master Audio (DTS-HD MA), another lossless surround sound codec.

Dolby TrueHD logo as introduced in 2012.

The Dolby TrueHD specification provides for up to 16 discrete audio channels, each with a sampling rate of up to 192 kHz and sample depth of up to 24 bits. Dolby's compression mechanism for TrueHD is Meridian Lossless Packing (MLP); prior to Dolby TrueHD, MLP was used for the DVD-Audio format, although the two formats' respective implementations of MLP are not mutually compatible. A Dolby TrueHD audio stream varies in bitrate, as does any other losslessly compressed audio format.

Like its predecessor, Dolby TrueHD's bitstream carries program metadata, or non-audio information that a decoder uses to modify its interpretation of the audio data. Dolby TrueHD metadata may include, for example, audio normalization or dynamic range compression. In addition, Dolby Atmos, a multi-dimensional surround format encoded using Dolby TrueHD, can embed more advanced metadata to spatially place sound objects in an Atmos-compatible speaker system.

Blu-ray Disc

In the Blu-ray Disc specification, Dolby TrueHD tracks may carry up to 8 discrete audio channels (7.1 surround) of 24-bit audio at 96 kHz, or up to 6 channels (5.1 surround) at 192 kHz.[1] The maximum bitrate of an audio stream including metadata is 18 Mbit/s (instantaneous, since it is variable bitrate),[2] and a TrueHD frame is either 1/1200 seconds long (for 48000 Hz, 96000 Hz or 192000 Hz) or 1/1102.5 seconds long (for 44100 Hz, 88200 Hz or 176400 Hz). Uncompressed (LPCM) it can be >35 Mbit/s. Any Blu-ray player or AV receiver that can decode TrueHD can also mix a multi-channel TrueHD track into any smaller amount of channels for final playback (for example, a 7.1 track to a 5.1 output, or a 5.1 track to a stereo output) by merging discrete channels' signals (except the low-frequency effects channel, the ".1," in a stereo mixdown, which is discarded due to its sound not playing back well without a dedicated subwoofer).

Dolby TrueHD is an optional codec, which means that Blu-ray hardware may decode it, but also may not (for example, inexpensive or early players, Blu-ray computer software, or pre–Blu-ray AV receivers). Consequently, all Blu-rays that include Dolby TrueHD audio also include a fail-safe track of Dolby Digital (AC-3), a mandatory codec. Unlike the competing DTS-HD Master Audio, which encodes its primary (optional) track in terms of differences from the companion mandatory track, a Dolby TrueHD-equipped Blu-ray's primary and companion tracks are redundant; the Dolby TrueHD bitstream has no data in common with the AC-3 bitstream, but AC-3 is used to construct E-AC3 stream. Similarly to DTS-HD MA, however, Dolby TrueHD's dual tracks are opaque to the user; a Blu-ray player loaded with a Dolby TrueHD disc will automatically fall back to AC-3 if it cannot decode or pass through the lossless bitstream, with no explicit selection required (or offered).

Dolby TrueHD's prominence relative to DTS-HD MA began to decline around 2010.[3] It has experienced a mild resurgence as the encoding used for Dolby Atmos audio (especially in Ultra HD Blu-ray titles),[4] but DTS-HD MA is still more common on titles with non-Atmos lossless audio. Regardless, publishers such as Paramount Home Entertainment[5][6][7] and Funimation[8][9][10] still use Dolby TrueHD for their releases.

Transport

Audio encoded using Dolby TrueHD may be transported to A/V receivers in one of three ways depending on player and/or receiver support:[11][12]

  • Over 6 or 8 RCA connectors as analog audio, using the player's internal decoder and digital-to-analog converter (DAC).
  • Over HDMI 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 Dolby TrueHD bitstream encapsulated in MAT[4] (Metadata-Enhanced Audio Transport) frames, with decoding and DAC both done by the AV receiver. This is the transport mode mandated by Dolby Atmos.[4]

Because S/PDIF does not have sufficient bandwidth to carry a TrueHD bitstream, or more than two channels of PCM audio, using S/PDIF requires either falling back to a disc's Dolby Digital track or mixing the TrueHD track down to stereo.

References
  1. "Dolby TrueHD". Dolby Laboratories. Retrieved August 22, 2014.
  2. "Technology Dolby Audio Dolby TrueHD | Dolby Developer". developer.dolby.com. Retrieved 2021-08-30.
  3. "DTS-HD Master Audio Becoming the Blu-ray Standard". Blu-raystats.com. January 15, 2010. Archived from the original on November 13, 2016. Retrieved November 15, 2010.
  4. "Dolby Atmos for the Home Theater" (PDF). Dolby Laboratories. Archived from the original (PDF) on May 21, 2020. Retrieved 2018-06-29.
  5. Wonder Park Blu-ray Release Date June 18, 2019, retrieved 2021-05-18
  6. Like a Boss Blu-ray Release Date April 21, 2020, retrieved 2021-05-18
  7. Popeye Blu-ray Release Date December 1, 2020, retrieved 2021-05-18
  8. Kakushigoto: The Complete Season Blu-ray Release Date August 31, 2021, retrieved 2021-07-31
  9. Show by Rock!! Mashumairesh!!: Season Three Blu-ray Release Date August 24, 2021, retrieved 2021-07-31
  10. A Certain Magical Index: Season Two Blu-ray Release Date August 17, 2021, retrieved 2021-07-31
  11. Maestra, Rodolfo La (August 8, 2006). "HDMI Part 5 - Audio in HDMI Versions". HDTV Magazine. Archived from the original on May 12, 2008. Retrieved November 15, 2010.
  12. "HDMI versions". 17 January 2017. Thursday, 19 January 2017
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.