Here are 4 OSX audio related tricks that Pro Tools users may find useful..
1. Change The Audio I/O
You can the audio I/O from the menu bar. Hold Option and click on the speaker symbol to quickly change the audio I/O.
2. Adjust The Volume In Smaller Increments
When you are using the keyboard to change the volume, if you would like to change the volume in smaller increments then hold down Shift > Option and hey presto.
3. Adjust The Volume Silently
Sometime the increasing/decreasing volume sound can be really annoying. To get rid of it, just hold down Shift when changing the volume to temporarily mute the feedback sounds. You can of course disable all annoying sounds in the System Preferences.
4. Quickly Force Quit Pro Tools:
This is my favourite. When you right click on the Pro Tools icon in the dock, just hold down Option to change the option “quit” to “force quit”. Remember that this will cause that the application is shutting down without saving.