Adaptive TRansform Acoustic Coding. A lossy, 5:1-formatsplit-band perceptual coding and compression scheme for reducing data to be written on a MiniDisc. ATRAC offers a 5:1 data reduction ratio in the case of Minidisc, employing the equivalent of 52 filter bands for spectral analysis and quantization. Later versions of ATRAC vary the size of the sample blocks dynamically between 11.6ms and 1.45ms according to the input signal to allow for temporal masking, providing extremely good resulting sound.