| 摘要 |
A telephone system comprising a sidetone controlling function is provided to compare a detected call current with a preset sidetone reference value, and to automatically and properly control size of a sidetone through a switching circuit according to the compared results, thereby maintaining an optimum speech quality without forcibly suppressing an output signal of a receiving sound. A side tone voltage detector(7) detects a call current detected through a telephone line to compare the detected call current with a preset reference value, and outputs one of plural sidetone select switching signals according to the compared results. A switching controller(8) outputs a sidetone select control signal for selecting a sidetone level control function according to the plural sidetone select switching signals. The first sidetone processor(9) attenuates an output level of a sidetone at certain level, and outputs the attenuated sidetone. The second sidetone processor(10) amplifies the output level of the sidetone at certain level, and outputs the amplified sidetone.
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