Abstract: Howling, which occurs when amplifying a target sound collected by a first microphone through an amplification section and outputting the amplified sound as an intensified sound from a loudspeaker, is suppressed. A first power spectrum is produced according to a first acoustic signal output from the first microphone collecting a sound. A second power spectrum is produced according to a second acoustic signal of a sound including at least the intensified sound and not including the target sound. Then, the first acoustic signal is filtered based on the first power spectrum and the second power spectrum to output only an acoustic signal of the target sound to the amplification section.

Abstract: A signal generating section generates a main signal and a noise reference signal. A determining section determines whether a level ratio is larger than a predetermined value. An adaptive filter section generates a signal indicative of a signal component of a target sound included in the noise reference signal generated by the signal generating section, and learns a filter coefficient only when the determining section determines that the level ratio is larger than the predetermined value. A subtracting section subtracts the signal generated by the adaptive filter section from the noise reference signal. A noise suppressing section suppresses a signal component of noise included in the main signal by using the main signal and the noise reference signal after subtraction by the subtracting section.