Minimum Word Classification Error Training of HMMs for Automatic Speech Recognition

This paper presents a novel discriminative training criterion, minimum word classification error (MWCE). By localizing conventional string-level MCE loss function to word-level, a more direct measure of empirical word classification error is approximated and minimized. Because the word-level criterion better matches performance evaluation criteria such as WER, an improved word recognition performance can be achieved. We evaluated and compared MWCE criterion in a unified DT framework, with other commonly-used criteria including MCE, MMI, MWE, and MPE. Experiments on TIMIT and WS JO evaluation tasks suggest that word-level MWCE criterion can achieve consistently better results than string-level MCE. MWCE even outperforms other substring-level criteria on the above two tasks, including MWE and MPE.