Normalized amplitude modulation features for large vocabulary noise-robust speech recognition

Abstract

Background noise and channel degradations seriously constrain the performance of state-of-the-art speech recognition systems. Studies comparing human speech recognition performance with automatic speech recognition systems indicate that the human auditory system is highly robust against background noise and channel variabilities compared to automated systems. A traditional way to add robustness to a speech recognition system is to construct a robust feature set for the speech recognition model. In this work, we present an amplitude modulation feature derived from Teager’s nonlinear energy operator that is power normalized and cosine transformed to produce normalized modulation cepstral coefficient (NMCC) features. The proposed NMCC features are
compared with respect to state-of-the-art noise-robust features in Aurora-2 and a renoised Wall Street Journal (WSJ) corpus. The
WSJ word-recognition experiments were performed on both a clean and artificially renoised WSJ corpus using SRI’s DECIPHER
large vocabulary speech recognition system. The experiments were performed under three train-test conditions: (a) matched, (b)
mismatched, and (c) multi-conditioned. The Aurora-2 digit recognition task was performed using the standard HTK recognizer
distributed with Aurora-2. Our results indicate that the proposed NMCC features demonstrated noise robustness in almost all the
training-test conditions of renoised WSJ data and also improved digit recognition accuracies for Aurora-2 compared to the MFCCs
and state-of-the-art noise-robust features.