Phase setting section sets virtual phases in a frequency series of an audio signal. Unit wave extraction section extracts, from the frequency series, a unit wave of one cyclic period defined by the set virtual phases, for each of a plurality of time points. First generation section generates velocity information corresponding to a degree of compression/expansion, to a predetermined length, of the unit wave. Second generation section generates shape information indicative of a shape of a frequency spectrum of the unit wave having been adjusted. Variation component impartment section generates a variation component by use of the velocity information and shape information generated for the individual time points.