MacBook and MacBook Pro (13-inch): How to use the combination audio port for an audio input device
Learn how to select the functionality of the combination audio port on your MacBook and MacBook Pro (13-inch).
When you put a mini-stereo plug in the combination audio port, your computer will automatically detect the device and use the device as an analog output device.
If you want to set up the port as an audio input device, you can manually switch from using the port as an output device in the Sound pane of System Preferences. Follow these steps:
Plug the input audio device into the combination audio port using the proper adapter cable.
From the Apple () menu, choose System Preferences.
Choose Sound from the View menu.
Click the Input tab.
Change the "Use audio for:" menu selection from Sound Output to the Sound Input.
The device type should change from "Internal Microphone/Built-in Input" to "Line In/Built-in Input."
Your audio input device is now ready to use.