Method for changing speed and pitch of speech and speech synthesis system

A method comprising:

• setting sections having a first window length based on a first hop length in a first speech signal;
• generating spectrograms by performing a short-time Fourier transformation on the sections;
• determining a playback rate and a pitch change rate to change a speed and a pitch of the first speech signal, respectively;
• generating speech signals of sections having a second window length based on a second hop length from the spectrograms;
• and
• generating a second speech signal of which a speed and a pitch are changed on the speech signals of the sections,
• wherein a ratio between the first hop length and the second hop length is set to be equal to a value of the playback rate, and wherein a ratio between the first window length and the second window length is set to be equal to a value of the pitch change rate.