Core Audio is Apple computer's new audio technology for OS X. Devices have core audio drivers associated with them. If a driver is installed in your system you will be able to edit its parameters from this dialog.
Select the source or audio input from the Input Source pop-up.
If you plan on using features like software play through or to have synchronized recording and playback, it is best to set this to same device as selected in the Digital Audio Setup dialog after the direct support radio button. If you do not have an input device or want to route the jukebox to a different output device, set your audio output device here.
Audio Buffer Packet Size
The Audio Buffer Packet Size setting determines how many samples are sent to the audio device at a time. This has a direct correlation to latency of automation, and software audio thru. Set too small or too big, however can have adverse effects on the system.
The Clock Source is only available for digitial audio inputs and allows a system to sync to external digital audio.
Default Record Input Selection
The Record Left (Mono) and Record Right pop-up allow you to specify the default inputs. The inputs for audio tracks are specified in the track window's Audio Record Input Select field. The Audio Record Input Select field is exposed from the track window's down-pointing triangle directly to the left of the RMS in the track window. Clicking on the triangle brings up the Display Options submenu: