As Christoph pointed out, make sure that you have the latest driver for your device installed.
The first ting is to check is if OSX recognizes ("sees") your MIDI device. For that, go to your Utilities folder inside your Applications folder and launch the "Audio MIDI Setup" application. Under the Window menu select "Show MIDI Studio".
Hope that helpsEdgar Rothermich
- If you don't see the Yamaha device, then OSX has trouble recognizing the device. Check your cable and driver. If the device is not showing up there, then GarageBand won't see it either
- If you see the Yamaha device, then GarageBand should use it as a MIDI input. Connecting and re-connecting the Yamaha keyboard should prompt GarageBand with an Alert window that you have changed the number of MIDI inputs.
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