| Summary: | 碩士 === 國立清華大學 === 動力機械工程學系 === 103 === In this work, four delay-and-sum (DAS) beamformers formulated in the modal domain and the space domain for open and solid spherical apertures are examined via numerical simulations. The resulting beampatterns reveal that the mainlobe of the solid spherical DAS array is only slightly narrower than that of the open array, whereas the sidelobes of the modal domain array are significantly higher than the space domain array due to the discrete approximation of continuous spherical Fourier transformation. To verify the theory experimentally, a three-dimensionally printed spherical array on which 32 micro-electro-mechanical systems (MEMS) microphones are mounted is chosen for localization and separation of sound sources. To overcome the basis mismatch problem in signal separation, source localization is first carried out using Minimum Variance Distortionless Response (MVDR) beamformer or multiple signal classification (MUSIC) algorithm. Next, Tikhonov regularization (TIKR) and compressive sensing (CS) methods are used to extract the source signal amplitudes. Simulations and experiments are conducted to validate the proposed spherical array system. In particular, the experimental investigations include an objective Perceptual Evaluation of Speech Quality (PESQ) test and a subjective listening test. The experimental results demonstrate better sense of separation achieved by the CS approach than by the TIKR approach at the cost of slight distortion.
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