Noisy audio feature enhancement using audio-visual speech data

We investigate improving automatic speech recognition (ASR) in noisy conditions by enhancing noisy audio features using visual speech captured from the speaker's face. The enhancement is achieved by applying a linear filter to the concatenated vector of noisy audio and visual features, obtained by mean square error estimation of the clean audio features in a training stage. The performance of the enhanced audio features is evaluated on two ASR tasks: A connected digits task and speaker-independent, large-vocabulary, continuous speech recognition. In both cases and at sufficiently low signal-to-noise ratios (SNRs), ASR trained on the enhanced audio features significantly outperforms ASR trained on the noisy audio, achieving for example a 46% relative reduction in word error rate on the digits task at -3.5 dB SNR. However, the method fails to capture the full visual modality benefit to ASR, as demonstrated by its comparison to discriminant audio-visual feature fusion introduced in previous work.