PURPOSE: To adjust sound quality to obtain a sound steeper than the steep rising sound such as drum sound by adding a signal up to (2n+1)th power (n is an integral number being ≥1) of a high frequency component and an original audio signal, and outputting the result when a steep rising at a large level of a high frequency component exists in the original audio signal.

CONSTITUTION: When a detection means 9 detects the steep rise of an original audio signal or a high frequency component of an original audio signal passing through a filter means 3, a high frequency component (2n+1)th power (n is an integral number being 1 or over) formed by a signal processing means 7 and the original audio signal are added and outputted by an adder means 10. Thus, the relevant portion of the original audio signal is deformed so as to close to a rectangular wave and outputted, and in case of a sound with steep rise such as drum sound, the sound is adjusted to a steeper sound, and percussional sound is obtained.