QUOTE(Whelkman @ Aug 12 2007, 07:29)

Audacity's a good bet.
I'm looking at Audacity right now, seems promising.. But... Really slow.. First to import the mp3-files, 29 files @ 25-45 minutes each, and then to change the tempo -25%. So I'm making this one solution and hope to get more.

Thank you Whelkman.

QUOTE(slks @ Aug 12 2007, 09:09)

Audacity, GoldWave, or any other audio editor should be able to do this easily.
GoldWave had this "Batch Processing" atleast.. But how to change the tempo of it, to -25%.. I have no clue...