A resonator comprises a housing arranged in an intake member for defining an opening to communicate with an intake passage and a volume portion to communicate with the opening portion, a movable partition which can change the volume of the volume portion, and a movable cover associated with the movable partition for changing the opening area of the opening portion. The waveform has, during the first cycle group, an initial peak-to-peak voltage and, during each subsequent cycle group, a peak-to-peak voltage that may be substantially equal to or less than that of the previous cycle group. In the meantime, a scale note pitch of an additional sound or harmony sound to be added to the input sound is specified in accordance with a harmony mode selected by a user.