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 Master Audio is an optional audio format for Blu-ray Disc format exclusively. DTS-HD Master Audio has been steadily becoming the standard for Blu-ray lossless audio format.
One goal of the DTS-HD Master Audio format was to allow a bit-to-bit representation of the original movie's studio master soundtrack. To accomplish this, DTS-HD MA supports variable bit rates up to 24.5 Mbit/s on a Blu-ray Disc and up to 18.0 Mbit/s for HD DVD. The format supports a maximum of 192 kHz sampling frequency and 24-bit depth samples from 2 to 5.1 channels, and 96 kHz/24bit resolution up to 7.1 channels.
DTS-HD is capable of virtually any number of discrete channels (over 2000) but is limited by storage media.
According to DTS-HD White Paper, the DTS-HD Master Audio contains 2 data streams: the original DTS core stream and the additional "residual" stream which contains the "difference" between the original signal and the lossy compression DTS core stream. The audio signal is split into two paths at the input to the encoder. One path goes to the core encoder for backwards compatibility and is then decoded. The other path compares the original audio to the decoded core signal and generates residuals, which are data over and above what the core contains that is needed to restore the original audio as bit-for-bit identical to the original. The residual data is then encoded by a lossless encoder and packed together with the core. The decoding process is simply the reverse. Note that DTS-HD lossless audio coding is always variable bit rate.
DTS-HD Master Audio may be transported to AV receivers in 5.1, 6.1 or 7.1 channels, at lossless quality, in one of three ways depending on player and/or receiver support:
- Over 6, 7 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-, 7- 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 DTS-HD Master Audio bitstream, with decoding and DAC both done by the AV receiver.