ATRAC (Advanced TRansform Acoustic Coding) is the audio compression method developed by Sony for use with their MiniDisc portable audio system. It works similarly to MPEG-1 Audio Layer 3 (or MP3) by removing inaudible frequencies from the sound in order to remove data but retain audio quality. ATRAC1 uses a compression ratio of approximately 5:1 and a bitrate of approximately 292kbps. It is also said to be superior to MP3 in terms of sound quality.
The latest version of the ATRAC DSP is the ATRAC1/ATRAC3 DSP Type-S. The Type-S DSP incorporates the ATRAC1 Type-R DSP used on the latest Sony MD recorder models such as the MZ-R909, MZ-R910 and MZ-N NetMD series as well as the newly-developed ATRAC3 DSP which includes decoder-side improvements in order to give better quality to ATRAC3 (or MDLP) recordings. The Type-S DSP was announced by Sony in early 2002 and will be included on the MDS-JB980 and MDS-JE780 MD recording decks that are due for release in August, 2002.