Comment 8 for bug 1359803

I have the same issue.

Asus X450CA laptop with a single TRRS jack. External headphones work correctly, but the external microphone does not work at all. Only the built-in microphone (that hole next to the webcam) is detected. This has been happening since 13.10 (the first Ubuntu I installed on this laptop, which was brand-new at that time).

alsamixer shows: Master, Headphone, Speaker, PCM, Mic Boost, Mic Boost, S/PDIF, Capture, Auto-Mute Mode, Digital.

Interesting that it shows two "Mic Boost" sliders, but there is no option to switch to the external microphone. The only recording device is called "Capture".

alsa-info.sh output:
http://www.alsa-project.org/db/?f=3fca8420153cf1b5424b490cf0d58f65224c27c1

Kernel release: 3.19.0-16-generic

 0 [PCH ]: HDA-Intel - HDA Intel PCH
                      HDA Intel PCH at 0xf7e10000 irq 32

00:1b.0 Audio device: Intel Corporation 7 Series/C210 Series Chipset Family High Definition Audio Controller (rev 04)

Codec: Realtek ALC270

Other bug reports from other people:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1366639
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1382642
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/212378
https://askubuntu.com/questions/75828/external-microphone-not-working