| 摘要 |
A speakerphone system has a speaker and microphone in a common acoustic environment and electrically preceded and succeeded, respectively, by receive and transmit sections and adapted, respectively, to reproduce as sounds by such speaker signals passed through such receive section from a remote station, and to convert sounds sensed by such microphone into signals passed through such transmit section to such station. A computer derives from the signals from the microphone an electric quantity which is a measure of the average audible ambient noise level in such environment, and the computer uses such quantity as one factor among others in switching signal losses between such two sections so as to change the state of operation of the system between transmit and receive states. As an improvement, there is derived from such quantity a control signal which effects dynamic adjustment of the gain in the receive section so that the average level of the sounds reproduced by the speaker will increase as such noise level increases, and conversely (Automatic Level Control). Other improvements are to provide for the system(a) a plurality of individually selectable interface circuits for matching the system to differently designed two-way voice communication channels in the outside world, (b) an auxiliary microphone for picking up voice sounds in the environment to be reproduced by the speaker, (c) an additional speaker not subject to automatic level control, and (d) sound tones produced under manual control in the environment by the system either to aid an installer in adjusting the system or to provide a reminder that the system is "on.
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