I was facing this issue after converting my F180k to E975 . Other party would always say your voice is low and its breaking ,i was really pissed off hearing speak louder every time . I did lot of research and came across many threads but found no viable solution . I was pretty sure mic is ok and problem is software related because whenever i would record a video or my own voice it was very clear .I edited build.prop in many ways but nothing worked . After editing build.prop in many ways i finally found a solution and now mic gain is like it is supposed to be. Other party can hear me loud and clear with noise reduction function fully working .
How to Fix
1. Open System\build.prop using some root explorer (I suggest FX file explorer with root add on)
2. Remount system as R/W
3. Scroll down to # snapdragon value add feature
4. Further scroll 2 lines down
5. Find line "ro.qc.sdk.audio.fluencetype=none"
6. Change "none" of above line to "fluence"
7. Save file
It should work like a charm now .
This is for stock E975 rom or any other stock based rom . You may not find these lines in build.prop of CM or AOSP based rom .
NOTE: I have edited this thread because previous fix which i posted stopped working .