Windows 7 has some new audio settings which I haven\'t been able to control from my C# application. Specifically, within the Input (microphone) properties, there is a Levels Ta
The IAudioEndpointVolume interface might work for you. It has functions to get/set mute state and volume levels for a recording or playback device.
Reference: http://msdn.microsoft.com/en-us/library/windows/desktop/dd370892(v=vs.85).aspx