Pitch extraction device and pitch extraction method

A pitch extraction method comprising:

• dividing, by a computer, a first bit stream in encoded data into a plurality of sections each having a prescribed section length, the encoded data being obtained by performing entropy encoding on a residual signal calculated by performing linear prediction analysis on a sound signal;
• allocating, by the computer, a first value or a second value to each of the plurality of sections in the first bit stream in accordance with a bit value in each of the plurality of sections;
• generating, by the computer, a second bit stream obtained by re-encoding the first bit stream according to the first value and the second value that have been allocated to each of the plurality of sections in the first bit stream;
• calculating, by the computer, an autocorrelation sequence for the second bit stream;
• calculating, by the computer, an estimation value of a fundamental frequency of the sound signal in accordance with the autocorrelation sequence of the second bit stream;
• and
• outputting, by the computer, the estimation value as the fundamental frequency of the sound signal.