In Windows 7 and Vista, you can adjust the microphone volume in the 'Sound' Settings, which can be found either by right-clicking your speaker icon and selecting "Recording Devices" or by navigating to the Control Panel and selecting Hardware and Sound > Sound, then selecting the 'Recording' tab.
Once at this screen, you need to select 'Turtle Beach USB Headset', '[Headset] CHAT', or your PC's Line In/Microphone Input, then click the 'Properties' button. When the 'Microphone Properties' window appears, click the 'Levels' tab. You will see two separate controls: 'Microphone' and 'Microphone Boost'. You can then adjust the microphone volume to your liking.
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