Resolved Internal microphone volume too low

Hi,

I've got a Macbook Air 13 2012.
I've noticed that the internal microphone's volume is very low. So, in Skype calls nobody manages to hear me.
I tried a recording in GarageBand and the volume is also low.

The volume is set to the maximum in the preferences and the ambient noise reduction function is off.
This happens both with Mountain Lion and Mavericks.

Is this a software problem or a hardware problem?
Here in Europe, it's still under warranty (2 years). Should I take it to the shop?

In the meantime I'm using my iPhone's headphones and the microphone sound is good.

Seems nobody has a solution for this problem (or any info).

So, it's looks like a malfunction. Let's see what the shop says.