What is ATRAC 4.5 encoding?
ATRAC stands for Adaptive TRansform Acoustic Coding and was developed for SONY to be used in the MiniDisc format. ATRAC allows up to 80 minutes of stereo audio to be stored on a disc much smaller than a 12cm diameter CD. It achieves this by reducing the data rate to and from disc to approximately 20% of the 44.1, 16 bit PCM data rate associated with CD. ATRAC uses various psycho-acoustical phenomena such as masking to remove audio data that is considered to be undetectable by the human ear. The first versions of the ATRAC algorithm were not too effective, but version 4.5 has reached a stage of maturity whereby most find it is extremely difficult or near impossible to tell a difference between the audio quality of the compressed and the uncompressed signals. One should not confuse ATRAC 4.5 with the more recent ATRAC3. ATRAC3 uses 10:1 (MDLP2) or 20:1 (MDLP4) compression as compared to the ATRAC 4.5, which uses 5:1 compression and is much higher quality. ATRAC 3 relates more closely to
