Combined Differential Beamforming With Uniform Linear Microphone Arrays

While differential beamformers have been widely used in voice communication and human-machine speech interface systems to enhance speech signals of interest, how to design such beamformers that on the one hand can achieve the highest possible directivity factor (DF) and on the other hand are able to obtain a certain level of white noise gain (WNG), so that they are robust enough to sensors' self noise and array imperfections is still a challenging issue. This paper studies the problem of robust differential beamforming with small-size arrays to achieve a high DF. It presents a method for the design of differential beamformers with uniform linear arrays. We first generate differential pressure signals by applying the recently developed forward spatial difference operator to the outputs of the array with pressure sensors. The pressure microphone observation signals and the differential pressure signals are then put together, and a combined beamformer is subsequently designed, which consists of two sub-beamformers, one operates on the pressure microphone observations and the other on the differential pressure signals. A new class of combined differential beamformers are introduced, which can achieve different levels of compromises between DF and WNG using an adjustable parameter.