11. The method according to claim 10 , wherein corresponding two formant frequencies comprises, if the similarity is not above the threshold, generating a virtual formant having zero power and the same formant frequency as one of the two formant frequencies; and corresponding the virtual formant with the one of the two formant frequencies.
10. The method according to claim 9 , wherein corresponding each formant frequency comprises estimating a similarity of each formant frequency of the formant parameter between two of the corresponded frames; and corresponding two formant frequencies having a similarity above a threshold in the two corresponded frames.