Dolby TrueHD in the context of Lossless compression

Dolby Digital, originally synonymous with Dolby AC-3 (see below), is the name for a family of audio compression technologies developed by Dolby Laboratories. Called Dolby Stereo Digital until 1995, it uses lossy compression (except for Dolby TrueHD). The first use of Dolby Digital was to provide digital sound in cinemas from 35 mm film prints. It has since also been used for TV broadcast, radio broadcast via satellite, digital video streaming, DVDs, Blu-ray discs and game consoles.

Dolby AC-3 was the original version of the Dolby Digital codec. The basis of the Dolby AC-3 multi-channel audio coding standard is the modified discrete cosine transform (MDCT), a lossy audio compression algorithm. It is a modification of the discrete cosine transform (DCT) algorithm, which was proposed by Nasir Ahmed in 1972 for image compression. The DCT was adapted into the MDCT by J.P. Princen, A.W. Johnson and Alan B. Bradley at the University of Surrey in 1987.

TOSLINK (Toshiba Link) is a standardized optical fiber connector system. Generically known as optical audio, the most common use of the TOSLINK optical fiber connector is in consumer audio equipment in which the digital optical socket carries (transmits) a stream of digital audio signals from audio equipment (CD player, DVD player, Digital Audio Tape recorder, computer, video game console) to an AV receiver that can decode two channels of uncompressed, pulse-code modulated (PCM) audio; or decode compressed 5.1 or 7.1 surround sound audio signals, such as Dolby Digital and DTS. Unlike an HDMI connector cable, a TOSLINK optical fiber connector does not possess the bandwidth capacity to carry the uncompressed audio signals of Dolby TrueHD and of DTS-HD Master Audio, but it can carry up to 8 channels of PCM audio when used to connect two devices that use the ADAT Lightpipe standard.

Although the TOSLINK connector supports several media formats and physical standards, the most common digital audio connectors are the rectangular EIAJ/JEITA RC-5720 (also CP-1201 and JIS C5974-1993 F05). In a TOSLINK connector, the optical signal appears as a red light, with a peak wavelength of 650 nm. Depending on the type of modulated signal being carried, other optical wavelengths can be present.

DTS-HD Master Audio (DTS-HD MA; known as DTS++ before 2004) is a multi-channel, lossless audio codec developed by DTS as an extension of the lossy DTS Coherent Acoustics codec (DTS CA; usually itself referred to as just DTS). Rather than being an entirely new coding mechanism, DTS-HD MA encodes an audio master in lossy DTS first, then stores a concurrent stream of supplementary data representing whatever the DTS encoder discarded. This gives DTS-HD MA a lossy "core" able to be played back by devices that cannot decode the more complex lossless audio. DTS-HD MA's primary application is audio storage and playback for Blu-ray media; it competes in this respect with Dolby TrueHD, another lossless surround format.