A Timbre Equalization Scheme for Spatial Ambisonics Reproduction

Abstract

Spatial Ambisonics are a series of (3D) spatial sound reproduction systems based on spherical harmonics decomposition and each order approximation of sound field. Limited by Shannon-Nyquist spatial sampling theorem, spatial Ambisonics are able to reconstruct target sound field within some upper frequency limit and certain region. A higher order spatial Ambisonics exhibits a higher Shannon-Nyquist limit but is more complicated. Practical Ambisonics reproduction with appropriate order leads to errors in reconstructed sound field beyond the Shannon-Nyquist limit. These errors may give rise to timbre coloration in reproduction, although they influence little on perceived virtual source direction due to the dominant role of low-frequency interaural localization cues. In present work, an equalization method is proposed to reduce the timbre coloration in spatial Ambisonics reproduction. Above the upper frequency limit of spatial sampling theorem, the magnitudes of reproduction signals are equalized so that the overall power of these signals is equal to that of the target sound source. Analysis using Moore’s revised loudness model indicates that the proposed method reduces the deviation between the binaural loudness level spectra in Ambisonics reproduction and that of the target sound source. Psychoacoustic experiment validates that the proposed method reduces the timbre coloration without degrading the virtual source localization performance in reproduction.