Howto | turn a tune into a tone
Choose the tune
Make sure the song you want to use is already in your iTunes library. If it isn’t, open iTunes, choose File > Add To Library and add the track. Next, open GarageBand’s Media Browser using the icon of a camera and a musical note at the top-right corner. Select iTunes, then Music, locate the track you want and then drag it to the very beginning of the Audio 1 track.
Trim the track
A three-minute song is too long to use as a ringtone, so trim it to an appropriate length. Zoom out to see the whole track and then move the pointer to the bottom-right of the track. The pointer will change to the trim tool. Drag leftwards. You should see the audio shorten. In this example we’re going to trim it to just eight bars of music, so that we only have the main riff looping.
Check your loop
The orange bar right above your track is the selection marker. If you click the loop icon and then play, GarageBand will loop just that section. You can adjust the selection by dragging its edges. This is a good way to check that your loop will work as a ringtone. When you’re satisfied with it, choose Share > Ringtone to iTunes to export the loop in the correct format, ready to sync to your iPhone.