"spool them from end to end"

Put in the cassette player, fast forward all the way to the end, then rewind all the way back to the beginning. Only then play to transcribe to any other medium.

The reason for doing this is to reduce print-through - the phenomenon where a faint echo of the sound is transferred magnetically from one layer to the next while the tape is stored packed tightly on the spool.

It's also called "excercising" the tape and it's always done by professionals with any tape (even 2" open reel studio tape) that's been stored for a long time.

Anahata