Copyright © 2008 The Institute of Electronics, Information and Communication Engineers
Special Section on Robust Speech Processing in Realistic Environments -- Papers -- Noisy Speech Recognition |
Robust Speech Recognition by Model Adaptation and Normalization Using Pre-Observed Noise
1 The authors are with NTT Cyber Space Laboratories, NTT Corporation, Yokosuka-shi, 239–0847 Japan.
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Abstract |
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Users require speech recognition systems that offer rapid response and high accuracy concurrently. Speech recognition accuracy is degraded by additive noise, imposed by ambient noise, and convolutional noise, created by space transfer characteristics, especially in distant talking situations. Against each type of noise, existing model adaptation techniques achieve robustness by using HMM-composition and CMN (cepstral mean normalization). Since they need an additive noise sample as well as a user speech sample to generate the models required, they can not achieve rapid response, though it may be possible to catch just the additive noise in a previous step. In the previous step, the technique proposed herein uses just the additive noise to generate an adapted and normalized model against both types of noise. When the user's speech sample is captured, only online-CMN need be performed to start the recognition processing, so the technique offers rapid response. In addition, to cover the unpredictable S/N values possible in real applications, the technique creates several S/N HMMs. Simulations using artificial speech data show that the proposed technique increased the character correct rate by 11.62% compared to CMN.
Key Words: noise robustness, distant-talking, spectral subtraction, HMM-composition, cepstral mean normalization
Manuscript received July 4, 2007. Manuscript revised September 17, 2007.