Multiband envelope techniques for the removal of reverberation and noise from speech signals

Multiband envelope deconvolution, multiband envelope shaping, and multiband nonlinear processing (expansion) techniques for the removal of reverberation from speech signals recorded by a single microphone in rooms of different sizes were studied. The speech waveform was modelled as the product of a broad slow-varying amplitude contour (envelope function) with a phase function that incorporates the finer speech structure. In the dereverberation scheme the envelope of the reverberated signal (in a number of frequency bands) was restored to the shape of anechoic speech envelope. A realignment between the energy of the direct and reverberant signals is thus achieved. It is shown that the three techniques can be used for speech enhancement when room reverberation follows a smooth exponential decay, with no late, strong reflections.