Method and apparatus for processing signals of a spherical microphone array on a rigid sphere used for generating an ambisonics representation of the sound field

摘要

Spherical microphone arrays capture a three-dimensional sound field (P(Ωc,t) for generating an Ambisonics representation (Anm(t)), where the pressure distribution on the surface of the sphere is sampled by the capsules of the array. The impact of the microphones on the captured sound field is removed using the inverse microphone transfer function. The equalization of the transfer function of the microphone array is a big problem because the reciprocal of the transfer function causes high gains for small values in the transfer function and these small values are affected by transducer noise. The invention estimates (73) the signal-to-noise ratio between the average sound field power and the noise power from the microphone array capsules, computes (74) the average spatial signal power at the point of origin for a diffuse sound field, and designs in the frequency domain the frequency response of the equalization filter from the square root of the fraction of a given reference power and the simulated power at the point of origin.

主权项

1. A method for processing microphone capsule signals of a spherical microphone array on a rigid sphere, said method comprising:
converting said microphone capsule signals representing a pressure on the surface of said microphone array to a spherical harmonics or Ambisonics representation Anm(t); computing per wave number k an estimation of the time-variant signal-to-noise ratio SNR(k) of said microphone capsule signals, using the average source power |P0(k)|2 of the plane wave recorded from said microphone array and the corresponding noise power |Pnoise(k)|2 representing the spatially uncorrelated noise produced by analog processing in said microphone array; computing per wave number k the average spatial signal power at the point of origin for a diffuse sound field, using reference, aliasing and noise signal power components, and forming the frequency response of an equalization filter from the square root of the fraction of a given reference power and said average spatial signal power at the point of origin, and multiplying per wave number k said frequency response of said equalization filter by a transfer function, for each order n at discrete finite wave numbers k, of a noise minimizing filter derived from said estimation of the time-variant signal-to-noise ratio estimation SNR(k), and by an inverse transfer function of said microphone array, in order to get an adapted transfer function Fn,array(k); applying said adapted transfer function Fn,array(k) to said spherical harmonics or Ambisonics representation Anm(t) using a linear filter processing, resulting in adapted directional time domain coefficients dnm(t), wherein n denotes the Ambisonics order and index n runs from 0 to a finite order and m denotes the degree and index m runs from −n to n for each index n.