Double the trouble: handling noise and reverberation in far-field automatic speech recognition

Far-field microphone speech signals cause high error rates for automatic speech recognition systems, due to room reverberation and lower signal-to-noise ratios. We have observed large increases in speech recognition word error rates when using a far-field (3-6 feet) microphone in a conference room, in comparison with recordings from close-talking microphones. In an earlier paper, we showed improvements in far-field speech recognition performance using a longterm log spectral subtraction method to combat reverberation. This method is based on a principle similar to cepstral mean subtraction but uses a much longer analysis window (e.g., 1 s) in order to deal with reverberation. Here we show that a combination of short-term noise filtering and longterm log spectral subtraction can further reduce recognition word error rates.