The free software program Audacity will let you:
- loop play any part of a song
- speed up or slow down a song without changing pitch
- change pitch up or down without changing tempo
- literally hundreds of sound processing options ranging from compression to EQ to - -- volume normalization to canceling out vocals so you can practice your karaoke etc. etc.
- record whatever's coming into your computer be it your bass, vocals, a cassette tape, etc.
- save files in any format (wav, mp3, aac, flac, etc.)
- play a soundfile in one track and record a second track simultanously (good for making playalong demos)
I've often used it to change the key of songs I'm supposed to learn and save them out as mp3s.
I've often used it to slow down songs and loop the difficult passages so I can focus on them until I've got them.
It's like photoshop for sound files.
Spector club #243, Rickenbacker #487, Country Bassist #18, Eden #307