When dealing with bidirectional voice, the user has two devices he is dealing with:
- The microphone, used to capture his speech
- The speakers, used to convey the sounds from the remote participant(s) of the call
The problem begins when the microphone captures not only the person speaking locally, but also the voice coming out of the speakers. Along with the voice reverbrating from artifacts in the room and the walls themselves, this is known as acoustic echo.
This acoustic echo is something that has to be cancelled in calls, especially when these take place without headsets.
Acoustic echo cancellation is built into most VoIP solutions, including WebRTC.