So you got an OnePlus One phone. I also own one. This is definitely one of the best smartphones out there. It is capable of handling heavy games, multitasking etc with ease. Since last few months, while on call, the other person won't be able to hear me quite well. The reason, was unknown. Looked like the Mic was faulty. But it worked fine on Whats app calls, skype calls, sound recorder etc. So this was definitely not the Mic. I am from Visakhapatnam and there is no Oneplus Service Center here. Nearest one is 400kms away. 😛 Very close right? Hmm. Then I thought let me try calling the customer care number. And She said "It is a known issue sir, I can surely guide you to fix it right away.". Cool. BOOM!! So here is the solution she suggested, and it simply worked. Considering you are on latest Cyanogenmod OS. "Go to Setting-> Language & Input -> Google Voice Typing. Then "OK Google" Detection -> Disable "From Any Screen" option." That is it. Now your Oneplus One Mic not working while on call is fixed. Give it a try and let me know.