MP3 only, or ATRAC too?

If you are using a minidisc to record sounds, or if you have a library
of sounds made using a minidisc machine, you will have a collection of
ATRAC recordings.  If you choose a player that understands only MP3,
then all the files in the library will have to be translated from
ATRAC to MP3.  On the other hand, if your player understands both
ATRAC and MP3, no translation will be necessary.

As you might guess, Sony makes the players that understand both ATRAC
and MP3.  These players work with SonicStage, Sony's proprietary PC
software.  Some of Sony's MP3 machines use removeable Flash memory
(Memory Stick) and removeable gumstick batteries.