Beam shape, focus index, and localization error for performance evaluation of a multisensor stethoscope beamformer

This paper proposes methods for evaluating a multisensor system consisting of several stethoscope chest pieces simultaneously recording and storing audio data for computer-aided analysis. To illustrate this concept, we use a circular array of microphones in a free-field homogeneous medium and use delay-and-sum beamforming to combine the received signals. The evaluation methods shown here are applicable to any other non-homogeneous medium and beamforming technique. Beam shape, focus index, and localization error are the methods of performance evaluation discussed in this paper. Several beam shapes are shown and described. The proposed "focus index", a new performance metric, compares the power of signals received from different areas within the array and comes up with a numerical indicator of the focus achieved by the beamformer. This paper also describes a method for localizing a sound source in the near-field of a microphone array by comparing the delay between signals received at known microphone locations. Simulation as well as verification results are presented.