A study on joint beamforming and spectral enhancement for robust speech recognition in reverberant environments

This work evaluates multi-microphone beamforming and single-microphone spectral enhancement strategies to alleviate the reverberation effect for robust automatic speech recognition (ASR) systems in different reverberant environments characterized by different reverberation times T60 and direct-to-reverberation ratios (DRRs). The systems consist of minimum variance distortionless response (MVDR) beamformers in combination with minimum mean square error (MMSE) estimators, and late reverberation spectral variance (LRSV) estimators, the latter employing a generalized model of the room impulse response (RIR). Various system architectures are analyzed with a focus on optimal speech recognition performance. The system combining an MVDR beamformer and a subsequent MMSE estimator was found to lead to the best results, with relative reductions of 27.7% compared to the baseline system. This is attributed to a more accurate LRSV estimate from spatial averaging and diffuse field refinement for the MMSE estimator.