The most important factors affecting the perceived quality of an audio teleconferencing system are: 1) the intelligibility and overall sound quality of the transmitted and received speech, and 2) the degree to which the system allows conference participants to interact in a full-duplex fashion. Received speech quality is maximized with a loudspeaker system having low distortion and directional characteristics that provide a flat response in the vocal range at the listener position. To maximize the perceived sound quality of transmitted audio, room noise and reverberation pickup by the system microphones must be held to a minimum. To achieve this requirement, directional microphones can be used along with automatic microphone selection (AMS) systems which activate only the best microphone for a particular talker. To provide full-duplex interactivity, modern teleconference systems employ an acoustic echo canceller (AEC) which increases the radio of local-to-far-end speech transmitted to the remote site. However, combining an AEC with an AMS system is not straightforward. Until recently, the capability to merge these technologies has been available only for large-room systems having separate loudspeakers and microphones. In these applications a black box approach has been the norm in which systems are created by combining one of several commercially available automatic microphone mixers with a full-duplex teleconferencing system. This approach results in an overall system performance that is less than optimum. This paper presents alternative approaches that take full advantage of both technologies, resulting in superior audio teleconferencing systems.
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