An extrinsic vowel normalization method is proposed. In the method proposed, a-priori information referring to the first and second formant values (Fl and F2) of three vowels of each speaker is used. In order to obtain the normalized formant values of a given speaker's vowels in a given language it is necessary to: gather reference information on three vowels, for example [i,#,u]. This information corresponds to the Fl and F2 values for [i,