I have an Acer Aspire One AO255E Netbook and was having a problem with the internal microphone being 'muted' or 'turned off' while running both UNR 10.10 and Joli OS 1.2. I stumbled upon the answer and here it is: The Juli OS help files have you:

sudo apt-get update
sudo apt-get install pavucontrol
Alt+F2
(enter) pavucontrol

When the control box pops up, click on the 'Input' tab. You will see two sliders for input marked Front Left and Front Right. The problem is, the external 'input' jack (or line in) is STEREO, while the internal microphone is obviously MONO. If you use an external microphone, which I did, which had a stereo plug on it (which implies that the microphone was a stereo microphone, or had one microphone connected to both left and right channels) and it worked fine, while the internal microphone did not. Now, if you click the little 'lock' icon (which unlocks the sliders) and move one of the sliders (doesn't matter which one) to zero, all of a sudden, the internal microphone works! Then, click the little 'lock' icon again, to lock the sliders where they are. Later, if you do want to input some two channel stereo stuff, you have to run pavucontrol again, unlock the sliders, adjust them both for whatever gain you want, and away you go. This behavior is apparently completely undocumented (or not). Anyway, it worked for me!

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