Mic levels are very unstable and low on Macbook Pro Retina 13"

Hi forum members,

I from time to time have problems with that the microphone volume on my 2012 Macbook Pro 13" Retina, gets very very low. I.e. when using Skype.

It seems like an unstability with Mavericks.

Any way to fix this?

The volume gets very, very low (even though I have the mic input volume turned to the max), and it doesnt help to restart the laptop either.

Any idea? Way to fix this OSX bug ?