| 摘要 |
PURPOSE:To prevent the sending out of the external noise by providing a sensor microphone besides a main microphone and controlling a by-pass circuit of a main microphone by the result to compare the level of the signal of both microphones. CONSTITUTION:To a main microphone 1M, an amplifier 2M and an alternating current-direct current converting circuit 3M are successively connected, and the first signal system is obtained. Also to a sensor microphone 1S, an amplifier 2S and an alternating current-direct current converting circuit 3S are successively connected, and the second signal system is obtained. The direct current signal output of both systems are applied to a comparing circuit 4, the level is compared, and in accordance with the comparing results, transistors 7 and 8 are controlled by on and off. The transistor 7 is connected through a capacitor 9 to an output end of the amplifier 2M, and by turning on this, a by-pass circuit of the signal, which occurs at the microphone 1M, is formed. As the result, the sending out of the external noise is prevented. |
