A locus model of coarticulation in an HMM speech recognizer

A novel type of hidden Markov model (HMM) has been developed to account explicitly for the context-dependent vowel acoustic transitions in consonant-vowel and vowel consonant phonetic environments. The major difference between this type of HMM and the standard Gaussian HMM is that the Gaussian mean vectors associated with the vowel HMM states, which are intended to model the vowel acoustic transitions, are set to be linearly interpolated values between those of the vowel steady state and those of the assumed locus for the adjacent consonant. The locus vectors, one for each consonant except for /h/, are trained together with all other HMM parameters using the Baum-Welch algorithm. The training procedure is fully automatic and converges to a local maximum. The model is incorporated in a phonetically based 75000-word vocabulary speech recognizer and provides a modest improvement in recognition rate over the standard approach.<>