Mg. Rahim et al., A STUDY ON ROBUST UTTERANCE VERIFICATION FOR CONNECTED DIGITS RECOGNITION, The Journal of the Acoustical Society of America, 101(5), 1997, pp. 2892-2902
Utterance verification represents a key technology in the design of a
user-friendly speech recognition system. One essential element when de
signing such a system is the ability to maintain a uniform performance
over a wide range of acoustic conditions. An acoustic mismatch betwee
n training and testing conditions often results in an undesirable perf
ormance degradation This paper addresses the issue of robustness in ut
terance verification of a speech recognition system. Two techniques, n
amely signal bias removal (SBR) and on-line adaptation, are studied. T
he SBR algorithm is used to deal with global mismatch conditions cause
d by handset and channel differences. The on-line adaptation algorithm
is used to adjust verification threshold at runtime for achieving a d
esirable trade-off between false rejection and false alarm in new test
conditions. Various on-line adaptation schemes are investigated. We s
how that both supervised or unsupervised adaptation can effectively ad
just the verification threshold to achieve a desirable performance tra
de-off irrespective of the initial setting of the threshold. We report
on connected digit recognition/verification results for matched and m
ismatched training and testing conditions. At a 5% digit string reject
ion rate, the proposed robust utterance verification system gives a re
duction in string error rate between 32% and 35% over the conventional
system, while still correctly rejects over 99.9% of nonvocabulary utt
erances. (C) 1997 American Institute of Physics.