Teardowns I've Worked On
Answer to "Use of external mic thru audio jack"The Nexus 7 has a normal 3-pole headphone-only jack at the bottom, and two microphones: one on the top left (on a little daughterboard plugged into the mainboard) and one on the lower left edge (soldered directly to the mainboard) about 1" above the docking pins. I don't know why they chose to do that. It is possible to replace the jack with a 4-pole and reroute the top microphone through it so it behaves as you would expect, but it's not a simple hack and it requires a willingness to shred your warranty and the equipment & skill to work with small SMD parts and flex-cable. Also, physically fitting and securing a 4-pole jack will probably involve epoxy and a dremel in addition to soldering little jumper wires. The Realtek ALC5642 - the (micro|head)phone driver chip - has Echo Cancellation and Noise Suppression built-in; one potential issue is whether the boost gain on the microphones (which is software selectable when the chip is used in PCs) is fine the way it is set, or if it can be tweaked. I haven't...