Believe it or not in 2015 some people still insist on using the smartphone for phone calls. All kidding aside, there is one unique issue that seems to be taking place with the Lumia 950 (and maybe just with the AT&T version).
Some users have noticed that during a phone call there is a very noticeable echo. Such occurrences sometimes happen when there is a bad connection, but this one seems to be reproducible. Luckily, a temporary workaround has been discovered.
In our forums, rickms80 figured out that by disabling the hands-free Hey Cortana voice-activation calls will no longer have an echo. Others have since confirmed the finding observing that turning off the feature resolves the issue until Microsoft patches it.
Hey Cortana is Microsoft's hands-free and passive listening service that lets users activate Cortana with just their voice. It is similar to OK Google and Siri functions on newer iPhones.
The reasoning behind the bug now makes sense as rickms80 explains:
"When the Hey Cortana feature is enabled it's "Always Listening." I'm confident that when the phone is "listening" the mics are tuned, so they're extremely sensitive to listen for "hey cortana." For some reason, this sensitive mic tuning is carried over into an incoming call, a bug of course."
Interestingly, we have not seen the same complaint about the Lumia 950 XL, so this may be an isolated incident. However, if you are experiencing the echo, you now know how to use a workaround. Fingers crossed the latest Insider release addresses this problem. That update is expected early this week.
To turn off Hey Cortana (which is off by default) you can read our guide above that shows the steps to activate and deactivate the service.
Source: Windows Central Forums; Thanks, Justice R., for the tip