| 摘要 |
PURPOSE:To obtain sound volume in accordance with the amount of external noise, by controlling the gain of an amplifier through a signal which is obtained from the subtraction of an output of speaker from a signal detected at a microphone. CONSTITUTION:A microphone 1 detects speaker sound and external noise. On the other hand, a signal corresponding to the speaker sound is picked up at a car-mounted audio equipment 4, it is detected at a wave detection circuit 5, and levels lower than a specified level are cut off at a level setting circuit 6. Only noise component can be given to the input of an integral network, by controlling a switching circuit 3 with the output signal of the level setting circuit 6. A gain control voltage is obtained by integrating the noise component at an integral network. The sound volume can be adjusted automatically in accordance with noise through this voltage. |
