Comment 17 for bug 1384952

I fixed this on my U7 with the info in this post.

https://forums.gentoo.org/viewtopic-t-1025106-start-0.html

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For posterity in case the form post disappears...

I found my answer here:

https://wiki.archlinux.org/index.php/PulseAudio/Troubleshooting#Microphone_not_detected_by_PulseAudio

The summary:

I edited /etc/pulse/default.pa to add the line:

Code:
load-module module-alsa-source device=hw:2,1

...since "arecord -l" showed that my missing mic was Card 2, Device 1

This newly-added line has to precede the lines:

Code:
### Automatically load driver modules depending on the hardware available
.ifexists module-udev-detect.so
load-module module-udev-detect

...in my case, this wound up being Line 52 of default.pa

I hope this can help someone else!