When you add a song into GarageBand from iTunes, you can cut it up and play with it a bit, but what about changing the tempo of the song? You'll notice that adjusting the tempo does not change the tempo of your iTunes added song. So how can you get around this? Here's how you do it.
- Drag in the song from iTunes, or record yourself.
- Select the song and press Control-Option-G and deselect the song.
- The song now turns purple, and you can open up the track editor and check the check box that says Follow Tempo & Pitch.