Steerable differential beamformers with planar microphone arrays
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RESEARCH
Open Access
Steerable differential beamformers with planar microphone arrays Gongping Huang1
, Jingdong Chen2* , Jacob Benesty3 , Israel Cohen1 and Xudong Zhao2
Abstract Humanoid robots require to use microphone arrays to acquire speech signals from the human communication partner while suppressing noise, reverberation, and interferences. Unlike many other applications, microphone arrays in humanoid robots have to face the restrictions in size and geometry. To address these challenges, this paper presents an approach to differential beamforming with arbitrary planar array geometries. The major contributions of this work are as follows: (1) a method is presented to design differential beamformers, which works for regular geometries such as linear, circular, and concentric circular ones, as well as irregular geometries, as long as the sensors’ positions are given or can be measured; (2) fundamental requirements for the design of different orders of linear differential microphone arrays (DMAs), partially steerable DMAs, fully steerable DMAs, and robust DMAs are discussed; (3) the validity and limitations of the Jacobi-Anger expansion approximation is analyzed, where we discuss how to achieve an optimal approximation by properly choosing the reference point; and (4) we show how to design an Nth-order DMA with 2N microphones using the Jacobi-Anger expansion. Keywords: Robot audition, Microphone arrays, Beamforming, Differential beamforming, Frequency-invariant beampattern
1 Introduction It has long been a dream of researchers and engineers to create humanoid robots, which can communicate naturally with humans through speech and language. A prerequisite for this is the ability to acquire speech from the human communication partner with high fidelity/quality and, meanwhile, mitigate or even eliminate the effects of background noise, acoustic feedback, interferences, reverberation, and robot ego noise. This requires to use sensor arrays with multiple microphones arranged into a certain geometry. Unlike many well-studied applications such as teleconferencing, microphone arrays for robot audition are limited by size and geometry [1–5]. Therefore, how to design small arrays with a flexible geometry and the associated beamforming algorithms that can process broadband speech signals is a critical problem *Correspondence: [email protected] Center of Intelligent Acoustics and Immersive Communications, Northwestern Polytechnical University, 127 Youyi West Road, 710072 Xi’an, China Full list of author information is available at the end of the article 2
[6–13]. Among different types of available arrays, differential microphone arrays (DMAs), which are designed to measure the differentials of the sound pressure field, are more appropriate for robot audition since they are small in size and can achieve high directivity and frequencyinvariant beampatterns [14–23]. From the early efforts of designing linear DMAs in a multistage manner [24, 25], to the recently developed null-constraint-based linear DMAs in the short-
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