Support Vector Machines for Phoneme Classification

In this thesis, Support Vector Machines (SVMs) are applied to the problem of phoneme classification. Given a sequence of acoustic observations and 40 phoneme targets, the task is to classify each observation to one of these targets. Since this task involves multiple classes, one of the main hurdles SVMs must overcome is to extend the inherently binary SVMs to the multi-class case. To do this, several methods are proposed, and their generalisation abilities are measured. It is found that even though some generalisation is lost in the transition, this can still lead to effective classifiers. In addition, a refinement to the SVMs is made to derive estimated posterior probabilities from classifications. Since almost all speech recognition systems are based on statistical models, this is necessary if SVMs are to be used in a full speech recognition system. The best accuracy found was 71.4%, which is competitive with the best results found in literature.