Some Practical Aspects of Stereo Teleconferencing System Implementation

When people with normal hearing converse in a room where many people are speaking simultaneously, their binaural hearing enables them to focus in on particular talkers according to the directions from which those talkers’ voices are coming. They can do this even when the signal-to-background-noise ratio is very low; noise, in this case being the voices of those ignored. This phenomenon of human audio perception is aptly called the cocktail party effect. In monophonic teleconferencing systems, this aid to audio communication is lost across the connection. A listener on one side hears all of the talkers of the far side coming from the same direction — the direction from a single local loudspeaker. So, when people on the far side talk simultaneously, it is impossible for the local listener to spatially separate their voices as he or she normally would. A stereo connection would solve this problem because with stereo the local listener (when located in the “sweet spot” — that area where the stereo effect is most clearly perceived) hears a reconstruction of the leftright positioning of the sound from the far side. Until very recently though, teleconferencing systems have been limited to monophonic connections because stereo acoustic echo cancellation was problematic [121]. However, with the advent of new techniques (see Chap. 5) such systems are now quite realizable.