Increasing the environment-awareness of rake beamforming for directive acoustic sources

Speech signals captured by distant microphones in enclosures are typically deteriorated by reverberation and background noise. Commonly, the quality of the signals is enhanced applying delay and sum beamforming (or variants) to a microphone array. However, under particular conditions, the multi-path acoustic propagation leading to reverberation is not completely detrimental and can be used in a constructive way. In this direction, mirrored (virtual) microphones have been successfully applied in various research areas. In addition, the majority of naturally occurring sound sources, such as the human speaker, presents a certain degree of radiation directivity, which, coupled with data-independent beamforming, has been shown to slightly increase the captured speech quality. Building upon the concepts of environment awareness and the acoustic rake receiver, this paper investigates the use of mirrored microphones, associated to isolated and strong reflections, in combination with source directivity, to further improve the captured speech quality. Real-data gathered with a linear nested array, as well as simulated data, are used to test the proposed scheme, showing superior performance with respect to similar state of the art solutions.