Energy-Preserving Ambisonic Decoding

Ambisonics with height is a three-dimensional sound field reproduction technique for spherical loudspeaker arrangements surrounding the reproduction area. It employs spherical harmonics up to a given order to expand incident sound fields with a limited angular resolution. The expansion coefficients describe the spatial sound scene. For reproduction, these coefficients are decoded to a set of surrounding loudspeakers. Common decoding approaches either sample the spherical harmonic excitation at the loudspeaker positions or match the excitation modes of a continuous sound field to those of the loudspeakers. For well-designed spherical loudspeaker arrays, both decoding approaches achieve good perceptual localization of virtual sound sources. However, both approaches perform unsatisfactorily with non-uniformly arranged arrays. Sounds from directions with only sparse loudspeaker coverage appear with altered loudness levels. This distracting effect results from variations in the decoded energy. The present article demonstrates an improved decoding technique, which preserves the decoded energy. Using available objective estimators, the localization qualities of these energy-preserving decoders are shown to lie between both common decoding approaches.