5th European Conference on Speech Communication and Technology

Rhodes, Greece
September 22-25, 1997

Selection of the Most Effective Set of Subword Units for an HMM-Based Speech Recognition System

Anastasios Tsopanoglou (1), Nikos Fakotakis (2)

(1) KNOWLEDGE S.A., Human Machine Communication Dept., Patras, Greece
(2) Wire Communications Laboratory (WCL), Electrical & Computer Engineering Dept., University of Patras, Greece

In this work we describe several approaches to determine an effective set of subword units for modeling the spoken Greek language. We tried to form a concrete set of basic units which must have the capability of giving a unique phonetic transcription for every input utterance. The results of an extensive set of experiments showed that the use of longer units than phonemes can lead to a significant improvement in a system's performance. Three sets of subword units were finally formed regarding the way we combined the 42 phonemes of the Greek Language. The three approaches showed better results than the baseline phoneme-based system and the most effective one proved to be the second approach in which we used two-phoneme combinations of the types non-vowel/vowel and non-vowel/non- vowel. The phoneme recognition rate of the system increased almost by 9% (reaching a level of 78.65%) for the best situation compared to the baseline system.

Full Paper

Bibliographic reference.  Tsopanoglou, Anastasios / Fakotakis, Nikos (1997): "Selection of the most effective set of subword units for an HMM-based speech recognition system", In EUROSPEECH-1997, 1231-1234.