When the recorded sound is muffled or too quiet (Windows XP)
Double-click the Sound and Audio Devices icon in Control Panel.
The Volume Control window will open, then click Properties under Options.
Select Recording, and in the volume control list below, check โStereo Mixโ and click OK.
If the sound is muffled, lower the Stereo Mix volume. If the sound is too quiet, increase the Stereo Mix volume.
Stereo Mix is a feature provided by the sound driver, so with some sound drivers, even if you increase the Stereo Mix volume, the sound may still be too quiet. In that case, increase the system volume as well.