| 摘要 |
PURPOSE:To attain excellent automatic sound volume control in audible sense by applying a detected noise component to a time constant circuit having a time constant different depending on the increase/decrease in noise and controlling the sound volume by the output. CONSTITUTION:A sound in a cabin including noise detected by a microphone 11 is amplified by an amplifier 1, detected by a detector 5 and smoothed into a DC by a time constant circuit 13. Similarly, an audio signal is smoothed by a detector 5' and a time constant circuit 13'. Both the DC signals are subjected to substraction by a subtractor 14, the audio component iseliminated and only the noise component is extracted. The noise component controls an electronic volume 2 via a voltage/current converter 16, a current mirror 15 and a time constant circuit 17. Further, a variable impedance circuit 18 is connected to an output of the current mirror 15 to increase the time constant of the time constant circuit 17 when noise increases and to decrease the time constant when the noise decreases. Thus, the audible sense is improved. |
