Directional Audio Coding (DirAC) is an efficient technique to capture and reproduce spatial sound on the basis of a downmix audio signal, direction of arrival, and diffuseness of sound. In practice, these parameters are determined using arrays of omnidirectional microphones. The main drawback of such configurations is that the estimates are reliable only in a certain frequency range, which depends on the array size. To overcome this problem and cover large bandwidths, we propose concentric arrays of different sizes. We derive optimal joint estimators for the DirAC parameters with respect to the mean squared error. We address the problem of choosing the optimal array sizes for specific applications such as teleconferencing and we verify our findings with measurements.
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