System Preferences - Sound
The Sound preferences allow you to set options to control the system and alert sounds, output and input devices, and volume.The Sound preference has three parts to it: Sound Effects, Output, and Input. You can set the system volume while in any of these windows. To set the system volume, drag the slider to the desired volume. This sets the maximum volume for all sounds. To mute the volume, simple check the box next to Mute.
By checking the box next to Show volume in menu bar, you will get a sound volume menu in the menu bar for quick access to setting the volume.
Access the volume in the menu bar:
Choosing an Alert Sound
Click the Sound Effects Tab
Select a sound from the list. After selecting a sound it will play to give you an example of your selection.
Setting output device options
Click the Output tab
Select an option from the list that is presented
Set the balance of the speakers by moving the slider left to right.
Setting input device options
Click the Input tab
Select an option from the list that is presented
Set the input volume by moving the slider left to right. The further right the slider is, the more sensitive the microphone will be.