GarageBand for iOS (iPad): Play Touch Instruments using a Bluetooth MIDI device
You can connect a compatible Bluetooth® MIDI device to your iPad, and use it to play and control Touch Instruments in GarageBand.
Tap the Song Settings button in the control bar.
Tap Advanced, then tap Bluetooth MIDI Devices.
Tap the name of the device you want to connect, then tap the Connect switch on.
To stop using the device, tap the Connect switch off.