Low microphone sensitivity during calls

My Honor 5C appears to have low microphone sensitivity when making a call (the other party can't hear me very well), however if I switch to loudspeaker mode when call is in progress then the microphone level is OK. This seems like a software issue.

I have seen on the internet turning off noise cancellation may be the fix but I am not sure how to do this. I can't see anything about Audio in Engineering mode.

Any help would be appreciated.