| 摘要 |
PURPOSE:To prevent sinking and howling without spoiling a natural sensation during a telephone call, by decreasing a gain when the level of an input signal is lower than a prescribed value. CONSTITUTION:An input signal is applied to a terminal (a), passed through an attenuating circuit, and outputted from a terminal (b). A DC voltage proportional to the level of the input signal is applied to the gate terminal (c) of an FET which operates as a variable resistance. The extent of the attenuation of the attenuating circuit varies with a function of resistances R1 and R2 and a capacitor C1. The variation with the input signal is expressed like a straight line which is discontinuous at some level of the input signal. Namely, when the input signal is lower than a prescribed value, the attenuation is increased and when it exceeds the prescribed value, normal control is performed. |
