Position-invariant close-talking microphone array

Abstract

Close-talking microphones are commonly used for speech pick-up in high-noise environments since they can significantly improve the signal-to-noise ratio (SNR) relative to conventional pressure microphones. Increased SNR is based on the assumption that unwanted noise sources are in the far field. However, close-talking microphones have to be carefully positioned or otherwise they can have reduced SNR improvement. A new close-talking microphone array is proposed that is orientation invariant with respect to the attenuation of far-field noise sources. It is shown that by appropriate processing of the close-talking microphone array signals, one can adaptively compensate for the distance and orientation of the microphone for a near-field source. The proposed close-talking array is based on a spatially orthonormal decomposition of the sound field for a near-field source. It consists of four or more pressure microphones that are mounted in the surface of a small rigid sphere. Finally, it is shown that decomposing the sound field into spatially orthonormal modes leads to a computationally efficient implementation. The orientation compensation is applicable not just to close-taking microphones but to directional microphones in general, e.g., podium microphones or hand-held vocal microphones.