Make sure the computer's audio input is set to USB Audio CODEC. To check this setting go to the Apple logo at the top left of your screen. Click on the logo and select System Settings > Sound. You should see USB Audio CODEC set for your Input.
You'll also need the Video Audio Switch set to option 2, which is labeled as (2) CASSETTE PLAYER
Now, make sure the Cassette Player is powered on before you play your tape.
At this point you should open QuickTime Player located in your Applications folder. To begin creating a new recording go to File > New Audio Recording.
Play your tape on the Cassette Player, turn up the volume in QuickTime to monitor your audio, and then press the red record button to digitize your analog audio content.
Press the stop button in QuickTime to save your content.
