| 摘要 |
PURPOSE:To exercise natural volume control which corresponds to the sense of hearing even when an ambient noise signal increases, by varying the time constant of an integral network in accordance with the level of a control signal based upon the output of the integral network. CONSTITUTION:While an audio signal S from a speaker 5 is detected through a sound detecting circuit 6, an input signal collected by a microphone 12 is detected by a noise detecting circuit 7 and both are applied to a subtracting circuit 8, respectively. The circuit 8 detects an ambient noise signal N, which is averaged by an integrator 9. In accordance with the output of the integrator 9, a control-voltage generating circuit 16 applies a control voltage to a volume controller 3 and a control-voltage detecting circuit 17. In accordance with the level of the detected control voltage, the circuit 17 controls the time constant of the circuit 9. Therefore, when the signal N increases and the control voltage rises, the time constant of the circuit 9 increases and the variation width of the con- trol voltage from the circuit 16 is suppressed small. Consequently, a sound heared from the speaker 5 is brought under natural volume control. |
