Microphone array beampattern characterization for hands-free speech applications

Abstract

Abstract-Spatial filtering is the fundamental characteristic of microphone array based signal acquisition, which plays an important role in applications such as speech enhancement and distant speech recognition. In the array processing literature, this property is formulated upon beam-pattern steering and it is characterized for narrowband signals.This paper proposes to characterize the microphone array broadband beam-pattern based on the average output of a steered beamformer for a broadband spectrum. Relying on this characterization, we derive the directivity beam-pattern of delayand-sum and superdirective beamformers for a linear as well as a circular microphone array. We further investigate how the broadband beam-pattern is linked to speech recognition feature extraction; hence, it can be used to evaluate distant speech recognition performance. The proposed theory is demonstrated with experiments on real data recordings.Index Terms-Broadband beam-pattern, Delay-and-sum beamformer, Superdirective beamformer, Distant speech recognition.

Enhanced diffuse field model for ad hoc microphone array calibration

“…We can see that the broadband pattern can be interpreted as a weighted average of the beamformer's output over the broadband spectrum [28]. Accordingly, the broadband power-pattern would be…”

Design Considerations When Accelerating an FPGA-Based Digital Microphone Array for Sound-Source Localization

“…The array pattern consists of four concentric subarrays of 4,8,16, and 24 MEMS microphones mounted on a 20 cm circular printed board (Figure 2). Each subarray is differently positioned in order to facilitate the capture of spatial acoustic information using a beamforming technique.…”

“…In fact, the characteristics of the main lobe when considering a single sound-source scenario determine the directivity of the microphone array. The definition of array directivity, , is proposed in [16] for broadband signals. The authors propose the use of ( ) as a metric of the quality of the array since depends on the main lobe shape and its capacity to unambiguously point to a specific bearing.…”

“…The authors propose the use of ( ) as a metric of the quality of the array since depends on the main lobe shape and its capacity to unambiguously point to a specific bearing. The definition of array directivity presented in [16] is adapted for 2D polar coordinates in [9] as follows:…”

“…This is enabled by grouping the input signals following their subarray structure. Therefore, instead of implementing one simple Filter-and-Sum of 52 microphones, there are four Filter-and-Sum operations in parallel for the 4,8,16, and 24 microphones. Their sum operation is firstly done locally for each subarray and afterwards between subarrays.…”