Along with iOS6 compatibility, Garageband for iOS recently acquired the ability to create ringtones. You can record anything you want or use a song from your music library to make the ringtone.
There are a ton of apps that allow you to create ringtones. Many of them are easier to use and offer features especially tuned for ringtone creation, so if you only want to make ringtones it may make more sense using one of them. On the other hand you may already have Garageband -- why not put it to use?
Like a lot of things in iOS, creating a ringtone isn't a difficult process but how you go about it isn't necessarily obvious either. So... to start launch Garageband. If you have a band, are mixing a song together, and just want to use the first part of it as the ringtone... you can skip to the end. For the rest of us we are either going to record something or use a song we already have on our iPad/iPhone.
Create a new song by tapping the "+" icon in the My Songs screen. Next, we need to pick a instrument... select Audio Recorder.
If the ringtone if going to be recorded live you are on the right screen. Tap the red record button to start.
The default settings will give you a good ringtone (4/4 Time Signature, 110 Tempo, 8 bars length). However at 8 bars the ringtone will not be as long as the 30 second maximum. To increase the length, tap the "+" icon in the time line, the tap "Section A - 8 bars".
Under Manual increase the bars to 11 any more will be cut off anyway.
Tap the fifth button on the top left (it should have five rectangles in it, the mixer). Here we can select what portion of the audio we recorded we want, add in other tracks, or just use music from our device.
Tap and drag the ends of the audio clip to select a portion. Drag from the middle to reposition the recording. I just want music from my library, so I'll delete the recording.
I have iTunes Music Match, so I need to make some adjustments since Garageband will only import music that is actually stored on the device and is not protected. So I need to download the music and I can't use music I purchased on iTunes (not exactly, for some reason some music I purchased still worked).
Pior to iOS6 Music Match songs downloaded when you played them. Now they stream, in fact the only way to download them now is through the album view. In the Music app, tap the iCloud button to download.
Back in Garageband, tap the Loop icon. Then select the Music section.
Select the album that is locally stored, then tap and drag a track on to the timeline.
Like the recording you can trim and reposition the song.
When you are happy with your ringtone, tap the "My Songs" button.
Tap "Edit", and select your ringtone.
Under the Sharing menu select Ringtone.
Don't forget to give it a unique name.
If you are planning to record something for the ringtone, using a wave editor will give you more control over the audio. You can add fades, amplify the sound, do some precision editing... create your master piece!