GarageBand for iOS (v2.0): How to select Inter-App Audio apps

With Inter-App Audio in GarageBand, you can route and record the sound output from third-party music apps directly into your GarageBand song.

The option to use Inter-App Audio is available only when at least one other Inter-App Audio app is installed on your device. To select an Inter-App Audio app, open the Instrument browser and tap Inter-App Audio Apps: