The Audio/MIDI pane contains the following preferences:
Output Device pop-up menu: Choose between any installed Core Audio devices, including the internal sound hardware.
Input Device pop-up menu: Choose between any installed Core Audio devices, including the internal sound hardware.
Effects: Audio Units checkbox: Allows you to use Audio Units plug-ins in your GarageBand projects. For more information, see Use Audio Units plug-ins with GarageBand.
MIDI Status: Reset MIDI Drivers button: Use if you have lost the connection to your MIDI devices.