Nested microphone array processing for parameter estimation in Directional Audio Coding

Directional audio coding (DirAC) is an efficient technique to capture and reproduce spatial sound on the basis of a downmix signal and side information, i. e., direction of arrival and diffuseness of the sound field expressed in time-frequency domain. The main drawback of using arrays of omnidirectional microphones to obtain these parameters is that reliable estimates are available only in a certain frequency range, which depends on the aperture. To overcome this problem and cover large audio bandwidths nested microphone arrays can be used. In this paper, we derive optimal estimators which combine the microphone signals to achieve the best possible estimation of the DirAC parameters with respect to the mean squared error.