ATRAC

ATRAC (Adaptive TRansform Acoustic Coding) is an audio compression algorithm used to store information on Minidiscs, developed by Sony. It uses quadrature mirror filters and modified discrete cosine transform to represent encoded audio.

Table of contents

1 ATRAC SP 2 ATRAC LP 3 ATRAC-3 LP-2 4 ATRAC-3 LP-4

ATRAC SP

Two stacked QMF split the signal into 3 parts:

• 0 ... 5.5125 kHz
• 5.5125...11.025 kHz
• 11.025...22.05 kHz

No joint stereo encoding.

Data rate is 266 Kb/s

ATRAC LP

Double play time, only mono.

ATRAC-3 LP-2

Three stacked QMF split the signal into 4 parts:

• 0 ... 2.75625 kHz
• 2.75625 ... 5.5125 kHz
• 5.5125...11.025 kHz
• 11.025...22.05 kHz

Joint stereo encoding. 132 kbit/s (yes, 15% below ATRAC SP/2)

ATRAC-3 LP-4

Similar to ATRAC-3 LP-2, but 66 kbit/s (half the data rate of ATRAC-3 LP-2). Low quality, similar to MP3 at 80...96 kbit/s.

see also: Lossy data compression, MP3