I have been exploring a lot about this set in Engineering Mode and quite often playing and changing different setting as resultant I got a set at the end which was really creating problems for me. I often use to listen very high sound of the person on other side or very low . So, I planned to fall back to factory and engineering Restore Setting. Although, it was tough decision as name suggest (Format NVRAM but keep calibrate.)
Experience was good in a sense that i was now with a set completely restored Engineering setting. Sound was pretty good and set seems to be booted first time.
Shocking news was I had lost all my contacts on phone memory(although 200 was still on sim but, additional had gone), My mobile memory was completely formatted and i lost some kool pics.
So, here go the procedure...if you want to go for it..if You are tired of sound issues..
Option 15 ..Format NVRAM but keep calibrate.
YOUR SET WILL TAKE SOME MOMENTS TO FORMAT AND THAN IT WILL REBOOT.... YOU ARE DONE...