Comparison of Techniques for Binaural Navigation of Higher-Order Ambisonic Soundfields

Soundfields that have been decomposed into spherical harmonics (i.e., encoded into higher-order ambisonics – HOA) can be rendered binaurally for off-center listening positions, but doing so requires additional processing to translate the listener and necessarily leads to increased reproduction errors as the listener navigates further away from the original expansion center. Three techniques for performing this navigation (simulating HOA playback and listener movement within a virtual loudspeaker array, computing and translating along plane-waves, and re-expanding the soundfield about the listener) are compared through numerical simulations of simple incident soundfields and evaluated in terms of both overall soundfield reconstruction accuracy and predicted localization. Results show that soundfield re-expansion achieves arbitrarily low reconstruction errors (relative to the original expansion) in the vicinity of the listener, whereas errors generated by virtual-HOA and plane-wave techniques necessarily impose additional restrictions on the navigable range. Results also suggest that soundfield re-expansion is the only technique capable of accurately generating high-frequency localization cues for off-center listening positions, although the frequencies and translation distances over which this is possible are strictly limited by the original expansion order.