The OS X System Preferences Sound window provides settings to choose Duet for Mac sound input and output. If you didn’t choose Duet for Mac sound I/O in step 3 of the Quickstart guide, you may do so in this window.
Go to the Apple menu > System Preferences. Open the Sound preference window by clicking on the speaker icon.
Click on the Output tab and select Duet in the Device window.
Click on the Input tab and select Duet in the Device window.
