Got the same issue
Just thought I'd chime in and say I have the same problem after the update to KitKat... Bummer
When recording the voice with whatever software there's no issue but callers say I sound very low/very far away from the mic. No difference between using the phone's mic or using a wired headset. Have yet to test a bluetooth headset (I do not have one).
I'm on Nexus 4, stock rom, 4.4.2. Any tips or ideas would be appreciated.