Fidelity of focal sound source reproduction by higher (9th) order ambisonics and perceptual effects of reproduction errors

Abstract

Higher-order ambisonic rendering is an increasingly common acoustic field reproduction technique that enables presentation of virtual sounds at nearly any location in 3D space, relatively unconstrained by the veridical locations of loudspeakers. We evaluated whether 3D sound reproduction through a 9thorder ambisonic system was sufficiently accurate to probe the limits of human spatial perception. In Experiment 1, we estimated minimum audible angles for human listeners at a variety of reference points on the horizontal plane. Our estimated values are similar to absolute thresholds obtained using single-channel free-field presentation for locations within ±51° on the horizontal plane, including values approaching 1° on the midline1, regardless of speaker density. This demonstrates the adequacy of the AudioDome for studies of human auditory spatial perception, at least for displacement in the horizontal plane. In Experiment 2 we estimated monaural and binaural localization cues by presenting linear chirp sweeps (0-22050 Hz) at the horizontal reference points tested in Experiment 1 and recorded ear canal signals through a head and torso simulator. Although localization cues for low-frequency components were well preserved, they were distorted for components above 4000 Hz. In Experiment 3 we provide evidence that these high-frequency distortions are processed as cues to elevation.