In voice communication, for example, in cellular telephones, due to restricted transmission bands, the quality of the received voice is much lower than the quality of the actual voice output by a user.
Accordingly, in known cellular telephones, to improve the quality of the received voice, signal processing, such as filtering, is performed on the received voice to adjust the frequency spectrum of the voice.
However, since the characteristic of the voice varies according to the user, the quality of voice having different frequency characteristics cannot be sufficiently improved merely by performing filtering on the received voice by using a filter having the same tap coefficient.