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Implementierung eines 64 Kanal Mikrofonarrays

Authors Hofer, D.
Year 2008
Thesis Type Diploma thesis
Topic Spatial Audio
Keywords Hardware, Aufnahmetechnik, signal processing
Abstract Beamforming, or spatial filtering, is a useful technique for designing a directivity pattern with microphone arrays. At least two microphones are required for this application. To improve spatial resolution the number of microphones needs to be further increased. The motivation throughout this thesis is to implement a low cost planar microphone array with 64 channels. The basic configuration is an 8x8 grid with variable spacing in between the grid points. This offers a varity of different geometric layouts with 64 microphones. A challenge, however, is to determine the positions of the 64 microphones in space. Consequently, the geometry shall be captured automatically. For this purpose, loudspeakers are placed in space at known positions. This work employs a tedrahedral source arrangement as stable spatial construction. Four loudspeakers are mounted on the vertices of the tetrahedron. Every loudspeaker individually transmits a measurement signal towards the microphone array. The acoustic delay to every microphone is determined with generalized cross correlation phasetransform (GCC-PHAT) and with linear regression. At the given speed of sound the acoustic delay corresponds to the length of the paths. From the path lengths, the coordinates of the microphones in space are determined with a numerical method (Simplex Method). The coordinates are required for an implementation of delay and sum beam formers or nearfield acoustical holography (NAH).
Supervisors Sontacchi, A., Zotter, F.