Two Microphone Array MVDR Beamforming with Controlled Beamwidth and Immunity to Gain Mismatch

Abstract:
This paper deals with applications that accomplish spatial filtering using two element microphone arrays and employing Minimum Variance Distortionless Response (MVDR) beam-forming. The frequency response of the microphones has limited accuracy, leading to mismatch between the microphone elements in both gain and phase, especially when making use of mass-production low-cost microphones. We introduce a method for controlling the beamwidth of the main lobe, bringing it to a specified constant width over a wide range of frequencies, thus helping to reduce sensitivity to phase mismatch. We also show a modified MVDR formula that remedies the susceptibility of the algorithm to gain mismatch. Index Terms — Microphone array, beamforming, minimum variance distortionless response (MVDR), frequency invariant beamwidth, microphone mismatch, phase mismatch, gain mismatch