PURPOSE: To simplify the constitution of an interpolation circuit interrupting an input audio signal and inserting an inclination signal during the period of mixing an impulsive noise to the input audio signal by constituting said circuit of resistors, capacitors and an in-phase amplifier.

CONSTITUTION: An audio signal Sa mixed with an impulsive noise is inputted to a low output impedance amplifier 19 through a delay circuit 18 and is also inputted to a control signal generating circuit CSG constituted of an impulsive noise detecting circuit 26 and a pulse shaping circuit 27. The CGS detects the pulse noise and generates a signal Sb during the period to disconnect an output switch 20 of the amplifier 19. Interpolation is performed by an inclination signal held by the interporation circuit consisting of the capacitors C24, 29, 23, the resistors R28, 22 and the in-phase amplifier 21 immediately before the disconnection of the switch 20 during the disconnection period of the switch 20 and a signal Sc is formed and outputted. If the values of the C24, 29, 23 and R28, 22 in the interpolation circuit are assumed as C1, C2, C3, R1 and R2 respectively, and the gain of the amplifier 21 is G, respective values are selected so as to satisfy the formulas I and II respectively.