This article is help Mac OS X 10.10 and 10.11 (existing or new) AudioBox 1818 Users who are running without AudioBox VSL Software who need to know how to change the Clock Source from Internal to either SPDIF or ADAT.
Step 1: Open up your Application Folder and then open up the Utilities Folder
Step 2: Once in the Utilities folder, run the "Audio MIDI Setup" Utility (icon looks like a single octave keyboard).
Step 3: You'll need to select your AudioBox VSL interface on the left column (see example below),
Make sure the AudioBox 1818 is selected as your default Sound Input Device and default Sound Input Device, open Cogwheel at the bottom of the left column, click it to select your AudioBox to be your default interface for Sound Input and Sound Output.
Step 4: Choosing Clock Source
To Choose Clock Source: (Internal, SPDIF or ADAT), open the drop down to choose Internal, SPDIF or ADAT.
If you've arrived at this tutorial and you're on Mac OS X 10.11 wondering why you're reading this, please review this article detailing AudioBox VSL software and Mac OS X 10.11.