5. The speech synthesis method according to claim 4 , further comprising detecting and processing motion of muscles around a mouth of the speaker when the sound signal is vocalized.
4. A speech synthesis method comprising: acquiring a sound signal including a speech signal vocalized by a speaker and a noise signal; recognizing speech vocalized by the speaker in the speech signal included in the sound signal; generating a spectrum of the acquired sound signal as a first spectrum; generating a second spectrum based on features of localized phonemes of the recognized speech signal so that the second spectrum does not contain a spectrum of the noise signal; generating a modified spectrum by multiplying the first spectrum by the second spectrum; and outputting a synthesized speech signal of the vocalized speech based on the modified spectrum.