Dolby Digital, originally synonymous with Dolby AC-3, is the name for what has now become a family of audio compression technologies developed by Dolby Laboratories. Formerly named Dolby Stereo Digital until 1995, except for Dolby TrueHD, the audio compression is lossy, based on the modified discrete cosine transform (MDCT) algorithm. The first use of Dolby Digital was to provide digital sound in cinemas from 35 mm film prints; today, it is now also used for applications such as TV broadcast, radio broadcast via satellite, digital video streaming, DVDs, Blu-ray discs and game consoles.
|Type||Audio compression format, lossy compression|
The main 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 first proposed by Nasir Ahmed in 1972 and was originally intended for image compression. The DCT was adapted into the modified discrete cosine transform (MDCT) by J.P. Princen, A.W. Johnson and Alan B. Bradley at the University of Surrey in 1987.
Dolby Laboratories adapted the MDCT algorithm along with perceptual coding principles to develop the AC-3 audio format for cinema needs. The AC-3 format was released as the Dolby Digital standard in February 1991. Dolby Digital was the earliest MDCT-based audio compression standard to be released, and was followed by other MDCT-based audio compression standards for home and portable usage, such as Sony's ATRAC (1992), the MP3 standard (1993) and AAC (1997).