A method of tracking formants defines a formant search space comprising
sets of formants to be searched. Formants are identified for a first
frame in the speech utterance by searching the entirety of the formant
search space using the codebook, and for the remaining frames by
searching the same space using both the codebook and the continuity
constraint across adjacent frames. Under one embodiment, the formants are
identified by mapping sets of formants into feature vectors and applying
the feature vectors to a model. Formants are also identified by applying
dynamic programming to search for the best sequence that optimally
satisfies the continuity constraint required by the model.