Mic problem

Hi. I've a problem with microphone of my Xiaomi Mi3: quality of sound is low. If I talk during a call, the quality is good but if I record a video, send a whatsapp vocal message there is a problem with audio: very low volume.

I'm trying to send a vocal message with Facebook Messenger but I can't send it and if try again to record a video, I am unable to record and save a video!

What's the problem?

I've MIUI 4.1.24