1. A signal processing method comprising the steps of: specifying a first section of a singing voice of a music based on temporal change of a pitch of singing voice data representing the singing voice or temporal change of a pitch in a score of the music; and modifying the singing voice data, wherein temporal change of at least one of the pitch, a volume, and a spectral envelope of the singing voice in the first section represented by the singing voice data is modified based on the singing voice data before the modifying step.