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Sound Source Localitzation with the Eigenmike Microphone Array

Authors Brandner, M.
Year 2014
Thesis Type Audio Engineering project
Topic Audio Signal Processing
Keywords audio recording
Abstract Directional detection of sound sources under defined ambience conditions using a spherical microphone array (Eigenmike) is examined. The used spatial detection algorithm correlates synthesized spherical wave spectra derived from theory with a set of concrete spherical spectra calculated from measured impulse responses. Thus, measurement signals were recorded with the 32 microphone equipped Eigenmike microphone array and two measurement sets were created for spatial sampling positions along an enclosing spherical surface with different radial distances. In order to simulate free field conditions and to compare the applicability of the proposed algorithm under real conditions the derived impulse responses are windowed adequately. Based on the Fourier transform of these resulting responses the calculation of the spherical wave spectra for specific source positions is possible. Under free- field conditions, the calculation of the synthesized spherical wave spectra of various spatial positions only depends on the structural properties of the microphone array and the position of the measured omnidirectional sound source. Correlation of measured and synthesized spherical wave spectra results in a data set with a maximum value for the sought direction of the sound source. Another aim of investigation is to understand the context between the size of the synthesized data – which serves as a lookup-table – and the directional accuracy. Within this thesis valuable information about functionality as well as the boundaries of the directional detection under defined spatial conditions with the spherical microphone array Eigenmike is given. The measurement is carried out at 612 equiangular source positions for the first measurement set and at 480 source positions for the second one. The results show a limited frequency resolution as expected, due to the arrangement of the microphones on the sphere. For the ideal case and a synthesis matrix including all measured source positions the algorithm yields for the full frequency range from 172 Hz up to the aliasing frequency (f alias = 5.2kHz) an diminishing median deviation error. The accuracy is directly connected to the spatial sampling (microphone capsule spacing) and the size of the synthesis matrix.
Supervisors Sontacchi, A.