Alternate phone models for conversational speech

This paper investigates the use of alternate phone models for the transcription of conversational telephone speech. The focus of this work is to explore alternative ways of modeling different manners of speaking so as to better cover the observed articulatory styles and pronunciation variants. Four alternate phone sets are compared ranging from 38 to 129 units. Two of the phone sets make use of syllable-position dependent phone models. The acoustic models were trained on 2300 hours of conversational telephone speech data from the Switchboard and Fisher corpora, and experimental results are reported on the EARS Dev04 test set which contains 3 hours of speech from 36 Fisher conversations. While no one particular phone set was found to outperform the others for a majority of speakers, the best overall performance was obtained with the original 48 phone set and a reduced 38 phone set, however combining the hypotheses of the individual models reduces the word error rate from 17.5% (original phone set) to 16.8%.