The internal microphone suddenly stopped working in Ubuntu 18.04 on my Lenovo Yoga 900 laptop. It was working for a while before so I suspect some update caused it to stop working.
The internal microphone is detected, but simply picks up no sound (note the input level in this screenshot). I have tried an external microphone and it successfully picks up sound.
My alsa info can be found here.
I had the same issue with yoga 920 and ubuntu 18.04, the mic was working on 16.04 but stopped after the upgrade.
I'm not entirely sure how I managed to resolve it though.
Firstly I added load-module module-echo-cancel to the end of /etc/pulse/default.pa and restarted pulseaudio, for no reason really, simply wanted to check whether it would help or not. It didn't.
Then I booted into my windows partition and disabled Dolby through Lenovo Vantage, the on/off switch can be found in the hardware/audio tab.
After I booted back into ubuntu the mic started working. Although maybe the pulseaudio+reboot fixed the mic, and not the Dolby disabling. Later I enabled Dolby back and the mic was still working in ubuntu.
