PURPOSE: To automatically adjust the sound volume of reproducing sound by providing a level detecting means to detect the signal level of a noise with prescribed frequency area out of noise in a vehicle room detected with a noise detecting means, and detecting the presence/absence of the conversation of parsons in the vehicle room.
CONSTITUTION: A band-pass filter 13 which passes only a frequency component with prescribed area out of output signals from an adder 12 and a level detector 14 are connected in series to the adder 12. The level detector 14 outputs a control signal to a voltage controller 8 corresponding to a detection result at a detecting part 15. Also, the passing frequency band of the band-pass filter 13 is set within a frequency range including the voice of the person ordinarily, and when the conversation of the persons in the vehicle room Rs is taken, it is inputted to the detecting part 15 of the level detector 14. When it is decided that an audio signal level exceeds a preset value by the control part 16 of the level detector 14, a reproducing sound volume from a speaker 4 is reduced by a prescribed volume.
KASHU YUKINOBU
ADACHI HISASHI
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