Patent ID: 7822600

Claim:
A method of extracting pitch information from an audio signal, comprising the steps of: when the audio signal is input, converting, by a frequency domain converter, the audio signal to a frequency domain (b) determining an optimum window size for extracting a pitch from the converted audio signal; (c) calculating a maximum value and a minimum value of the converted audio signal in optimum window using the determined optimum window size; (d) checking a variation between the maximum value and the minimum value and generating a staircase signal that has the minimum value in the variation and is used for filtering; (e) generating a residual signal by extracting the generated staircase signal from the converted audio signal; (f) generating pitch information by selecting a highest peak generated by performing a predetermined fold and summation process for folding and summing the residual signal; and (g) extracting the pitch information from the residual signal corresponding to the extraction result, wherein the staircase signal includes a plurality of flat signals continuously connected, each flat signal having a constant amplitude in a corresponding optimum window for a morphological operation.