A minimum distortion noise reduction algorithm with multiple microphones

The problem of noise reduction using multiple microphones has long been an active area of research. Over the past few decades, most efforts have been devoted to beamforming techniques, which aim at recovering the desired source signal from the outputs of an array of microphones. In order to work reasonably well in reverberant environments, this approach often requires such knowledge as the direction of arrival (DOA) or even the room impulse responses, which are difficult to acquire reliably in practice. In addition, beamforming has to compromise its noise reduction performance in order to achieve speech dereverberation at the same time. This paper presents a new multichannel algorithm for noise reduction, which formulates the problem as one of estimating the speech component observed at one microphone using the observations from all the available microphones. This new approach explicitly uses the idea of spatial-temporal prediction and achieves noise reduction in two steps. The first step is to determine a set of inter-sensor optimal spatial-temporal prediction transformations. These transformations are then exploited in the second step to form an optimal noise-reduction filter. In comparison with traditional beamforming techniques, this new method has many appealing properties: it does not require DOA information or any knowledge of either the reverberation condition or the channel impulse responses; the multiple microphones do not have to be arranged into a specific array geometry; it works the same for both the far-field and near-field cases; and, most importantly, it can produce very good and robust noise reduction with minimum speech distortion in practical environments. Furthermore, with this new approach, it is possible to apply postprocessing filtering for additional noise reduction when a specified level of speech distortion is allowed.