Adaptive Transform Acoustic Coding (ATRAC) is a family of proprietary audio compression algorithms developed by Sony.
MiniDisc was the first commercial product to incorporate ATRAC in 1992. ATRAC allowed a relatively small disc like MiniDisc to have the same running time as CD while storing audio information with minimal loss in perceptible quality.
Today ATRAC is used in many Sony-branded audio players. Improvements to the codec in the form of ATRAC3, ATRAC3plus and ATRAC Advanced Lossless followed in 1999, 2002 and 2006 respectively.
Other MiniDisc manufacturers such as Sharp and Panasonic also implemented their own versions of the ATRAC codec. The hybrid lossless compression scheme was added to the ATRAC family in 2006.