On near-field beamforming with smartphone-based ad-hoc microphone arrays

Spatial audio processing using ad-hoc microphone arrays that consist of mobile devices, such as smartphones, is an attractive approach for future speech and audio capturing applications. However, many issues including microphone localization, clock synchronization and gain equalization, need consideration before such ad-hoc arrays can be applied in practice. An additional issue that needs to be considered is the microphone directivity of the devices. In this paper, we present measured microphone responses for nine different smartphones and we demonstrate the effects of the directivity responses on beamforming using the minimum-variance distortionless response (MVDR) beamformer as an example. Our results show that the beamforming output can be degraded considerably if the microphone responses are not considered in the beamformer design.