| 摘要 |
PROBLEM TO BE SOLVED: To automatically adjust the transmission/reception voice signal intensity of a hands-free voice call device, using a portable telephone suitable for environment used and the used portable telephone device, and to obtain an optimum call state at all times. SOLUTION: This hands-free voice call device has a fundamental signal generating circuit 13 for outputting fundamental signals to a microphone 4 in order to start automatic adjustment in a no-call state, a control unit 12 adjusting respective gains of a 1st amplifying circuit 15, a 2nd amplifying circuit 16, a 3rd amplifying circuit 17, and a 4-th amplifying circuit 18, to make the level of sound outputted by the microphone 4 equal to a level which will not cause howling between the microphone 4 and a loudspeaker 5.
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