I just bought a new Lenovo P580 Ideapad yesterday and installed 12.04 64bit on it. I tried making a call with it and discovered that the built-in microphone wasn't working. I unmuted it in sound settings, and still nothing.

I did the following

:~$ cat /proc/asound/card0/codec#* | grep Codec 

Codec: Conexant CX20590

Codec: Intel PantherPoint HDMI

Followed some tips and ran

:~$ sudo gedit /etc/modprobe.d/alsa-base.conf

then added this to the end

options snd-hda-intel model=asus

I amplified the input sound with alsamixer to make sure...
When the input was amplified to max on alsamixer, the input signal was at a constant level (1/3 of max) which I'm guessing was the system's noise. This played back was a low frequency hum. I plugged in headphones that have a built-in mic and that worked, although it still had the humming in the background.

I changed the last line in alsa-base.conf to:

options snd-hda-intel model=thinkpad

which gave me the same result.

I'm not sure where to go from here, and any help would be greatly appreciated...