What you’ll basically be doing is telling iTunes to only listen to 30-seconds of the song of your choice. We’ll then use iTunes’ included exporting options to convert the full song into the 30-second .m4a file. Once that’s done, we’ll be changing the extension from .m4a to .m4r.

So go ahead and open up iTunes. To make sure that your song will be converted into the right format, go to the preferences for iTunes. In the ‘General’ tab, click on ‘Import Settings’. Under ‘Import Using’, make sure ‘AAC Encoder’ is selected. Click ‘OK’ when finished.

Find the song that you want to make a ringtone out of. Right-click on it and go to ‘Get Info’. Go to the ‘Options’ tab. Notice the ‘Start Time’ and ‘Stop Time’ boxes. Edit these numbers to be 30-seconds or less. When done choosing your segment, click on ‘OK’.

Now, right-click on your song once again, and click on ‘Create AAC Version’. iTunes will now make a new version of your song using the 30-second segment you have just chosen.

When it’s done converting, go to your library and find this new 30-second piece of audio. Right-click on it and go to “Show in Finder” (Mac OS X), or “Show in Explorer” (Windows). Change the extensions from .m4a to .m4r.

In Mac OS X, right-click on the file, and go to ‘Get Info’. Click on the arrow next to “Name & Extension”. Change the .m4a to .m4r. Delete this file from your iTunes library (without deleting the actual file if it asks), and drag the .m4r into it.

In Windows, you’ll need to ‘Show extensions for known files’ under the second tab in the ‘Tools’>’Folder Options’ section of any Explorer window (just open up the Recycle Bin and enable extensions). Next, right-click on your file and go to ‘Rename’. Change the.m4a to .m4r. Delete this file from your iTunes library (without deleting the actual file if it asks), and drag the .m4r into it.

You should now see your ringtone under the ‘Ringtones’ section on the left side of iTunes. Sync if up with your device and test it out in Settings>Sounds.