macbook – Can I connect a Yamaha Clavinova to an MBAir with a USB cable?

You must first install the Yamaha USB-MIDI driver:

This driver works for all Yamaha Clavina models with USB connection for MIDI.

If you have the driver installed, restart the Mac and plug the Mac's USB cable into the piano. Then turn on the piano. Finally, start GarageBand and the new MIDI device should be available.