Enhancing the Robustness of the Posterior-Based Confidence Measures Using Entropy Information for Speech Recognition

Yanqing SUN  Yu ZHOU  Qingwei ZHAO  Pengyuan ZHANG  Fuping PAN  Yonghong YAN 

Publication
IEICE TRANSACTIONS on Information and Systems  Vol.E93-D  No.9  pp.2431-2439
Publication Date: 2010/09/01
Online ISSN: 1745-1361
Print ISSN: 0916-8532
Type of Manuscript: Special Section PAPER (Special Section on Processing Natural Speech Variability for Improved Verbal Human-Computer Interaction)
Category: Robust Speech Recognition
Keyword: 
OOV,  speech recognition,  confidence measure,  entropy information,  phoneme-level posterior, 

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Summary: 
In this paper, the robustness of the posterior-based confidence measures is improved by utilizing entropy information, which is calculated for speech-unit-level posteriors using only the best recognition result, without requiring a larger computational load than conventional methods. Using different normalization methods, two posterior-based entropy confidence measures are proposed. Practical details are discussed for two typical levels of hidden Markov model (HMM)-based posterior confidence measures, and both levels are compared in terms of their performances. Experiments show that the entropy information results in significant improvements in the posterior-based confidence measures. The absolute improvements of the out-of-vocabulary (OOV) rejection rate are more than 20% for both the phoneme-level confidence measures and the state-level confidence measures for our embedded test sets, without a significant decline of the in-vocabulary accuracy.