From what I remeber when I owned a MiniDisc, there are ATRAC, ATRAC-2, ATRAC-3, and ATRAC-4. They are the methods of encoding/decoding in Sony branded MiniDisc units. ATRAC-3 seems to be the most widely used in modern Sony MiniDiscs.

If you bought a MiniDisc player/recorder from Sharp or another brand, it would have a different method of encoding/decoding (most likely).

-Rob
-----
12GB MK2 Blue 090000736 (6166 in the queue)