VOICE PROCESSING METHOD FOR PROCESSING VOICE SIGNAL REPRESENTING VOICE, VOICE PROCESSING DEVICE FOR PROCESSING VOICE SIGNAL REPRESENTING VOICE, AND RECORDING MEDIUM STORING PROGRAM FOR PROCESSING VOICE SIGNAL REPRESENTING VOICE

A voice processing method realized by a computer includes compressing forward a first steady period of a plurality of steady periods in a voice signal representing voice, and extending forward a transition period between the first steady period and a second steady period of the plurality of steady periods in the voice signal. Each of the plurality of steady periods is a period in which acoustic characteristics are temporally stable. The second steady period is a period immediately after the first steady period and has a pitch that is different from a pitch of the first steady period.