Instructions
Use the directional pad on the PS3 controller to scroll to the "Settings" menu on the PS3 XMB (the main menu).
Select "Accessory Settings" and press the "X" button.
Select "Audio Device Settings" and press the "X" button. Select "Input Device" and press the "X" button. Select the name of your headset and press the "X" button.
Select "Microphone Level." Speak into the microphone and press the "X" button to adjust the sensitivity until you are satisfied. The higher the number, the more sensitive the mic will be. Select "OK" and press the "X" button.