@naheed I have DTS Sound+ driver where i see all speakers and microphones connected + sensitivity on mics. Here I can see if the sensitivity is going up or not. I have noticed that it is only on this browser and not others, because i turned off Automatic gain on those but Opera doesn't have this setting.
In Control Panel i have already turned off access to take control over mic.

I would like to ask, why does Opera keep changing sensitivity of microphone? It becomes annoying and ruins calls when Opera sets sensitivity to 100% and other person/people hear my ventilator in Notebook. Is there any way to turn off automatic volume gain in Opera?