Adaptive Transform Acoustic Coding (ATRAC) is the generic name for audio compression algorithms developed by Sony. It is a family of proprietary algorithms developed by Sony Corporation. ATRAC was first incorporated into MiniDisc where it allowed the MiniDisc to have the same running time as CD and stored audio information with minimal loss in perceptible quality.
The coding is now used in many Sony-branded audio players. Improvements to the codec in the form of ATRAC3plus, ATRAC3 and ATRAC Advanced Lossless were brought in later on. The original bitrate of ATRAC was 292 kbit/s, which was designed to be close to CD quality. This bitrate was used on original MiniDiscs. ATRAC was later improved and CDs are now encoded at 1411.2 kbit/s, while lossless encoders encode CDs below 1000 kbit/s.
These algorithms were developed in order to deliver a tangible product that was capable of encoding at high speeds and with minimal power consumption. The design of the codec emphasizes on processing smaller numbers of samples at a time so that memory is saved at the cost compression efficiency.
ATRAC1 found its first application in Sony’s own theater format SDDS system in the 1990s. ATRAC3 is a hybrid subband-MDCT encoder like ATRAC1 and MP3, but has several differences. ATRAC3plus is used in Sony Hi-MD Walkman devices, Memory Stick players, VAIO Pocket, Network Walkman players, PS3 and PSP Console and ATRAC CD players.