Consequently, all Blu-rays that include Dolby TrueHD audio also include a fail-safe track of Dolby Digital (AC-3), a mandatory codec. 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).ĭolby 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). Uncompressed (LPCM) it can be >35 Mbit/s. The maximum bitrate of an audio stream including metadata is 18 Mbit/s (instantaneous, since it is variable bitrate), 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). 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. 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. Dolby TrueHD metadata may include, for example, audio normalization or dynamic range compression.
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.
A Dolby TrueHD audio stream varies in bitrate, as does any other losslessly compressed audio format. 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. The Dolby TrueHD specification provides for up to 16 discrete audio channels, each with a sampling rate of up to 192kHz and sample depth of up to 24 bits. Dolby TrueHD competes with DTS's DTS-HD Master Audio (DTS-HD MA), another lossless surround sound codec.
#AC3 CODEC FROM DOLBY PLUS#
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. Advanced lossless multi-channel audio codec Dolby TrueHD logo as introduced in 2012.ĭolby TrueHD is a lossless, multi-channel audio codec developed by Dolby Laboratories for home video, used principally in Blu-ray Disc and compatible hardware.
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