Comment 20 for bug 354705

The only solution to make microphone work is to install linux-backports-modules-alsa-generic...

Just go to:

Menu / System / Administration / Synaptic Package Manager

And search and mark for installation:

linux-backports-modules-alsa-generic

tip: if you have multiple versions click on the first and read the description which should inform what name to install...

If after the reboot and mic mute is off, still does not work, just go to terminal and type:

sudo nano /etc/modprobe.d/alsa-base.conf

and add or change the following:

options snd-hda-intel model=auto enable=yes

Then Ctrl+X, type Y to write and exit, reboot and mic will work.

Bye and have lots of fun with Ubuntu (the best).