Functional Design of a Voice-Switched Speakerphone

The original 1A Speakerphone System 1 used amplification in both its receive and transmit channels to compensate for the acoustic loss that was introduced by placing telephone instruments at greater distances from users than is normal with a handset. Among the operational difficulties 2,3 with such a system are talker echo and singing, particularly under reverberant room conditions. To avoid the limitations that are inherent in the simultaneous use of high gain in the two transmission channels, the voice-switched 3A Speakerphone System has been designed. It changes the gain in each of the two channels in accordance with the direction of the stronger speech signal. Voice-switching techniques have been used before in communica649 6GG THE BELL SYSTEM TECHNICAL JOURNAL, MAY 19(31 tion equipment, and have been found to possess limitations of their own. However, by application of certain design principles, 4 the new voiceswitched speakerphone substantially eliminates talker echo and singing, and greatly reduces objectionable side effects of the type often encountered with voice control. Moreover, these advantages are realized for a wide range of conditions. This paper is intended to provide a functional description of the 3A Speakerphone System and to show its performance characteristics, with particular emphasis on the parameters chosen to meet rather stringent performance objectives.