A frequency spectrum is detected by analyzing a frequency of a voice waveform
corresponding
to a voice synthesis unit formed of a phoneme or a phonemic chain. Local peaks
are detected on the frequency spectrum, and spectrum distribution regions including
the local peaks are designated. For each spectrum distribution region, amplitude
spectrum data representing an amplitude spectrum distribution depending on a frequency
axis and phase spectrum data representing a phase spectrum distribution depending
on the frequency axis are generated. The amplitude spectrum data is adjusted to
move the amplitude spectrum distribution represented by the amplitude spectrum
data along the frequency axis based on an input note pitch, and the phase spectrum
data is adjusted corresponding to the adjustment. Spectrum intensities are adjusted
to be along with a spectrum envelope corresponding to a desired tone color. The
adjusted amplitude and phase spectrum data are converted into a synthesized voice signal.