I have tested the mic/headphone jack on Asus x401u.
When I plug a headphone, the interface, Microphone and Headphones are shown, and headphone works.
When I plug a microphone,the interface, Microphone and Headphones are shown, but the active microphone is the built-in one.
If I plug a 4 ring jack into the hole, the interface, Microphone and Headphones are shown, but only headphone is active, the active microphone is still the built-in one.
Info from Tim Chen
I have tested the mic/headphone jack on Asus x401u.
When I plug a headphone, the interface, Microphone and Headphones are shown, and headphone works.
When I plug a microphone,the interface, Microphone and Headphones are shown, but the active microphone is the built-in one.
If I plug a 4 ring jack into the hole, the interface, Microphone and Headphones are shown, but only headphone is active, the active microphone is still the built-in one.