Creating a Ringtone for your iPhone from an MP3 using Garage Band

This uses Garage Band, which comes with Mac OS's.

1. Open Garage Band, create a new project
   
2. (You can delete the piano track by selecting it and then choosing Track → Delete Track from the Menu.)
   
3. Drag your .mp3 file from Finder to Garage Band. This creates a new Garage Band track.
   
4. (I sometimes need to click and drag the track off to the left so it starts at time zero.)
   
5. Play the track and find the start/stop portion you want. This must be less than 30 seconds (If it is slightly more, you can shrink it down later, but this will affect the sound quality a bit.)
   
6. Drag the end of the track (a colored box showing the volume of each portion of the audio--probably two lines for stereo) to the beginning and end of your portion.
   
   
   
   • You can zoom in with the logscale slider in the lower-left corner
     
   • You can double-click the track to see a larger version at the bottom of the screen
     
   
   
7. From the menu, choose Track → Show master track
   
8. Click on the master track to create points near the beginning and end of the track, and move the appropriate points down to fade the volume in and out.
   
9. Adjust the master volume (far right of the play controls) if necessary
   
10. If you need to, you can speed up or slow down your music with the following proceedure (source):
    
    
    
    1. Drag your audio file (MP3, M4A, ...) in GarageBand. It's shown as an orange track.
       
    2. Press Ctrl+Alt+G
       
    3. Click the audio track. It is now blue [Ed: purple]
       
    4. Check "Follow Tempo & Pitch" (this is in the wave editor section, which you get by clicking the scissors symbol next to the eye) [Ed: This is already open if you double-clicked the track earlier]
       
    5. Now change the tempo (next to the song time display) [Ed: Actually click the "tempo" number in the time display window]
       
    
    
11. Save your file. From the menu, choose Share → Export Song to Disk and save as an .m4a file.
    
12. Rename the .m4a file to .m4r (I had to do this in a terminal)
    
13. Import your .m4r file to iTunes, it shows up under the Ringtones category (in iTunes 8, at least)
    
14. Update the track info if you like
    
15. Sync with your iPhone