| 摘要 |
PROBLEM TO BE SOLVED: To ensure satisfactory speech quality by adjusting a volume by automatically level-adjusting the amplification gain of a transmission and reception signal to be amplified by an indoor master device according to the level of the noise around a residence front door where a front door slave device is set. SOLUTION: A reception signal from a slave device microphone 12 of a front door slave device 1 is inputted through a reception amplifier 32 of a speech circuit 26 of an indoor master device 2 to a receiving part 30b, and a transmission signal from a master device microphone 30a of the speech circuit is inputted through a transmission amplifier 31 to a slave device speaker 13 of the front door slave device so that speech can be established. The indoor master device is provided with a surrounding noise detecting circuit 33 for detecting the noise components around the front door slave device from the reception signal, and for outputting a DC signal proportional to it, a CPU 30 for receiving an output from the surrounding noise detecting circuit, and a gain controller 34 for respectively transmitting the transmission signal and reception signal level-adjusted according to the output from the surrounding noise detecting circuit to the slave device speaker and the receiving part under the control of the CPU.
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