Perceptually Transparent Binaural Auralization of Simulated Sound Fields

Contrary to geometric acoustics-based simulations where the spatial information is available in a tangible form, it is not straightforward to auralize wave-based simulations. A variety of methods have been proposed that compute the ear signals of a virtual listener with known head-related transfer functions from sampling either the sound pressure or the particle velocity (or both) of the simulated sound field. The available perceptual evaluation results of such methods are not comprehensive so that it is unclear what number and arrangement of sampling points is required for achieving perceptually transparent auralization, i.e.~for achieving an auralization that is perceptually indistinguishable from the ground truth. This article presents a perceptual evaluation of the most common binaural auralization methods with and without intermediate ambisonic representation of volumetrically sampled sound pressure or sound pressure and particle velocity sampled on spherical or cubical surfaces. Our results confirm that perceptually transparent auralization is possible if sound pressure and particle velocity are available at 289 sampling points on a spherical surface grid. Other grid geometries require considerably more points. All tested methods are available open source in the Chalmers Auralization Toolbox that accompanies this article.

Direct and Residual Subspace Decomposition of Spatial Room Impulse Responses

Psychoacoustic experiments have shown that directional properties of, in particular, the direct sound, salient reflections, and the late reverberation of an acoustic room response can have a distinct influence on the auditory perception of a given room. Spatial room impulse responses (SRIRs) capture those properties and thus are used for direction-dependent room acoustic analysis and virtual acoustic rendering. This work proposes a subspace method that decomposes SRIRs into a direct part, which comprises the direct sound and the salient reflections, and a residual, to facilitate enhanced analysis and rendering methods by providing individual access to these components. The proposed method is based on the generalized singular value decomposition and interprets the residual as noise that is to be separated from the other components of the reverberation. It utilizes a noise estimate to identify large generalized singular values, which are then attributed to the direct part. By advancing from the end of the SRIR toward the beginning while iteratively updating the noise estimate, the method is able to work with anisotropic and slowly time-varying reverberant sound fields. The proposed method does not require direction-of-arrival estimation of reflections and shows an improved separation of the direct part from the residual compared to an existing approach. A case study with measured SRIRs suggests a high robustness of the method under different acoustic conditions. A reference implementation is provided.

Binaural Audio Rendering in the Spherical Harmonic Domain: A Summary of the Mathematics and its Pitfalls

The present document reviews the mathematics behind binaural rendering of sound fields that are available as spherical harmonic expansion coefficients. This process is also known as binaural ambisonic decoding. We highlight that the details entail some amount peculiarity so that one has to be well aware of the precise definitions that are chosen for some of the involved quantities to obtain a consistent formulation.