| 摘要 |
PURPOSE:To improve the function of an apparatus by computing the ratio of a noise level to a sound volume level when a noise is generated during the operation of a color television image receiver, a car stereo apparatus, or the like, and if the ratio exceeds a reference ratio, increasing the sound volume of a speaker and then distoring the original sound volume in accordance with the disappearance of the noise. CONSTITUTION:A noise collected by a microphone is also inputted to an adder 10 together with a sound signal, the sound signal is canceled and only the noise component is outputted from the adder 10. The noise component is turned to a DC component by an integrating circuit 11, the DC component is converted into a digital signal by an A/D conversion circuit 12 and the digital signal is inputted to a controlling microcomputer 13 as a feedback signal expressing the noise level. The microcomputer 13 computes the ratio of the feedback signal to an initial sound volume level and determines the amplification degree of a 1st amplifier circuit 2 for determining the sound volume of the speaker 3. Thus the initial sound volume is held when the ratio is less than the reference one, and in the case of exceeding the reference ratio, the excess part is divided in each prescribed range and a control signal to the circuit 2 is corrected so as to increase the sound volume. |
