1) Launch both iTunes and GarageBand '08.
2) In iTunes, select the tune that you want to grab a short ringtone from. GarageBand can perform its magic with regular MP3 files or with AAC-encoded (iTunes standard) files.
3) In GarageBand, create a New Music Project. You can do this either by closing an open project and then clicking the Create New Music Project button on the GarageBand splash screen, or by selecting New from the File menu. Select a name (in the example shown below, it's the name of the song -- Thomas Dolby's "Blinded Me With Science") and location to save the GarageBand project, then click Create.
4) GarageBand displays a timeline with a single track. Delete the track (click on it, then choose Delete Track from the Track menu).
5) Drag your selected tune from iTunes to GarageBand. The song is imported into GarageBand and a new music track appears:
6) Now comes the fun part -- listen to the song and pick out a short (30-40 second) snippet for be your ringtone. I seem to always pick the most recognizable part of the tune, which is usually a refrain or some hook that is memorable. As you play through the song and find the start of the ringtone, pause the playback, and move the playhead (the vertical red line) to about the beginning of the ringtone. Don't worry about getting it exactly since you can do some additional editing later.
7) You'll need to delete the music ahead of the start of your ringtone. To do this, click on the track to select it, then choose Split from the Edit menu to split the track at the playhead. Click the blank GarageBand work area to deselect the track, then click on the portion you want to delete and press the Delete key on your keyboard.
8) Figure out where the end of your ringtone is going to be and make sure that the playhead is situated somewhere close to it. Use the same technique described in step 7 to delete the music after the end of your ringtone. At t his point, you should have a short piece of the overall song to turn into a ringtone.
9) Drag the beginning of the ringtone all the way to the left side of the track timeline. This is probably a good time to save your GarageBand project as well.
10) Now, let's soften the beginning and end of the ringtone to cover up any mistakes we've made in editing. To do this, click on the track automation button. See that set of five buttons at the beginning of the track? Click the little downward pointing triangle to bring up track automation. We're going to set a fade-in and fade-out on our ringtone.
11) About a half-second or so into the beginning of the track, click the volume line to create an edit point (left, below). Next, click and drag the beginning of the volume line down to zero volume (right, below -- -144.0 db).
What you've just done is create a fade-in for the beginning of the ringtone. It starts off silently and builds to full volume in about a second. If you find that you need the fade-in to be longer or shorter, just move that second volume dot left or right.
12) Do the same for the end of the ringtone. Click the volume line to create an edit point about one second from the end of the ringtone. Then click and drag the end of the volume line down to zero volume (-144.0 dB).
13) Listen to the entire ringtone to make sure that the fade-in and fade-out sound good. If they do, save the project one more time. If they don't, adjust the fades and then save the project.
14) Now we need to make sure that the ringtone will repeat as your phone rings. To do this, click on the button to turn the cycle region on and off. What? You don't know what button this is? Look at the bottom of the GarageBand window. See the controls (screenshot below)? It's the one on the far right that looks like a set of arrows chasing each other:
15) When you click that button, a bright yellow line appears above your track. Drag the right side of the line so that it matches the length of your ringtone (see below):
Doing this ensures that your ringtone will repeat over and over until you answer the phone or your caller goes to Visual Voice Mail. Do one final save of your project.
16) You're almost there! Go to the Share menu in GarageBand and choose "Send Ringtone to iTunes." Your project is converted to an iPhone ringtone that opens and plays in iTunes.
17) To move the ringtone to your iPhone, connect the iPhone while iTunes is open. Select the iPhone in the Devices list on the left side of iTunes, then click on the Ringtones tab. Make sure that Sync Ringtones is checked (see below), and select either All Ringtones or Selected Ringtones to sync with your iPhone. Click Sync, and your ringtone is copied to the iPhone.
Have fun filling up your iPhone with custom ringtones!