High order Ambisonics (HOA) is a flexible way to represent and analyze the sound field. In the process of the spherical Fourier transform, the microphone array need be uniformly scattered on the surface of a sphere, which limits the application of the theory. In this paper we introduce a HOA encoding method using the differential microphone arrays (DMAs). We obtain the particular beam patterns of different orders of spherical functions by the weighted sum of time-delayed outputs from closely-spaced differential microphone array. Then HOA coefficients are estimated by projecting the signals to the beam patterns. The coefficients calculated by the DMA are compared to the results derived from the theoretical spherical harmonics, which proves the effectiveness of our method.
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