Patent ID: 7457744

Claim:
An open-loop pitch estimation device of a speech CODEC which estimates a pitch of an input speech signal, the device comprising: an autocorrelation function calculation unit which calculates a normalized autocorrelation function from a perceptual weighing filtered speech signal; a maximum autocorrelation function and a lag estimation unit which receives the autocorrelation function and estimates a maximum autocorrelation function, a lag having the maximum autocorrelation function, candidates for the maximum autocorrelation function and lags corresponding to the candidates for the maximum autocorrelation function; a pitch candidate decision unit which decides a candidate for a pitch by using the ratio of the estimated maximum autocorrelation function to the candidates for the estimated maximum autocorrelation function, and the ratio of the lags having the estimated maximum autocorrelation function to the lags corresponding to the candidates for the estimated maximum autocorrelation function, and a lag smaller than a predetermined threshold as the candidate for a pitch; and a pitch estimation unit for producing a synthesized speech signal, which estimates a pitch between the candidate for a pitch and the lag corresponding to the estimated maximum autocorrelation function by using a pitch of a previous frame of the speech signal, wherein the pitch estimation unit estimates a lag that is nearest to the pitch of the previous frame between a lag that is smaller than the predetermined threshold and the lag having the maximum autocorrelation function.