PURPOSE: To provide a method attaining the reproduction with more fidelity by determining the signal of a power required to vibrate a diaphragm from the vibration result of the diaphragm of a microphone by calculation and processing the determined signal as a signal to be amplified.

CONSTITUTION: A trigger 9 provides a timing to extract a change for a very small time and a processing timing to each device and the conversion and arithmetic operation are conducted at this timing. A digital signal converted by an A/D converter 10 is given to a subtractor 11. The subtractor 11 subtracts the received data with data received just precedingly. The received data are stored for succeeding subtraction. The subtracted data are given to a multiplier 12, in which the data are multiplied with a reciprocal of the sampling time and the resulting data are given to a D/A converter 13, where digital data are converted into analog data. Since the vibration is damped actively by using the signal to reproduce a rate of overtone with more fidelity.