Skype always irritated me with its automatic microphone volume changes. The Windows version has the ability to disable this option in the preferences pane, but the Mac version does not. Today, I spent some time trying to solve this problem. After some searching on net, I found a solution for the Windows version which also works on the Mac.
Quit Skype and open the folloving file with TextEdit: ~/Library » Application Support » Skype » shared.xml. At the end of the document, you'll see this section:
Simply change this section to look like this (adding one new line):
<VoiceEng> <MicVolume>77</MicVolume> </VoiceEng>
AGC means Automatic Gain Control, and setting it to 0 disables this feature. Set it to 1 if you want to enable it again. The MicVolume can range from 0 (mute) to 255 (full volume). Save the file and start Skype.
<VoiceEng> <AGC>0</AGC> <MicVolume>100</MicVolume> </VoiceEng>
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