The following controls are provided on the Master Output window:
Output Source -- contains a list of available output sources. You check and uncheck sources to turn them on and off. Your choices are Built-in Speaker, Headphone, and Line Out. This list can grow to accommodate additional output devices. Volume and balance levels apply to all sources simultaneously, not to individual sources to turn them on and off.
Volume slider --for setting the master volume for all sources. The absolute level is displayed in a text label next to the control (the value is 50 in the figure above.) The displayed value changes as the slider is moved up and down.
Balance slider -- for setting the balance for all sources.
Mute -- for simultaneously muting all output sources.