Spatial Resolution of Late Reverberation in Virtual Acoustic Environments

Abstract

Late reverberation involves the superposition of many sound reflections, approaching the properties of a diffuse sound field. Since the spatially resolved perception of individual late reflections is impossible, simplifications can potentially be made for modelling late reverberation in room acoustics simulations with reduced spatial resolution. Such simplifications are desired for interactive, real-time virtual acoustic environments with applications in hearing research and for the evaluation of hearing supportive devices. In this context, the number and spatial arrangement of loudspeakers used for playback additionally affect spatial resolution. The current study assessed the minimum number of spatially evenly distributed virtual late reverberation sources required to perceptually approximate spatially highly resolved isotropic and anisotropic late reverberation and to technically approximate a spherically isotropic sound field. The spatial resolution of the rendering was systematically reduced by using subsets of the loudspeakers of an 86-channel spherical loudspeaker array in an anechoic chamber, onto which virtual reverberation sources were mapped using vector base amplitude panning. It was tested whether listeners can distinguish lower spatial resolutions of reproduction of late reverberation from the highest achievable spatial resolution in different simulated rooms. The rendering of early reflections remained unchanged. The coherence of the sound field across a pair of microphones at ear and behind-the-ear hearing device distance was assessed to separate the effects of number of virtual sources and loudspeaker array geometry. Results show that between 12 and 24 reverberation sources are required for the rendering of late reverberation in virtual acoustic environments.

Computationally-Efficient Simulation of Late Reverberation for Inhomogeneous Boundary Conditions and Coupled Rooms

“…In addition to being compatible with arbitrary geometry, a benefit of the generalized approach over the shoebox approach is the gradually increasing ILD for six VRS and a performance for 12 VRS, which is generally more similar to 96 VRS. The results of the current technical evaluation support the perceptual evaluation in [33] showing that 24 VRS are sufficient for rendering anisotropic late reverberation in the tested conditions.…”

“…Although an isotropic late reverberant field is approximated in the case of a completely homogeneous distribution of absorption coefficients at all boundaries, a more critical case regarding spatial resolution of late reverberation occurs for inhomogenously distributed absorption coefficients and in the case of coupled (sub-) volumes with connecting openings. Such a critical test case was assessed in [33], using a spatial mapping method for inhomogeneous boundary conditions in shoebox shaped rooms [34]. They have shown that 12-24 VRS are perceptually sufficient in a single room with anisotropic late reverberation, depending on the stimulus.…”

“…They have shown that 12-24 VRS are perceptually sufficient in a single room with anisotropic late reverberation, depending on the stimulus. Although [33] provides an estimate of the perceptually required spatial resolution for anisotropic late reverberation, there is no comparable computationally efficient method available that is also applicable to morecomplex room geometry and coupled rooms (or generally coupled volumes with connecting openings).…”

“…In a first step, spatial rendering of late reverberation was addressed in a simulated room with one highly absorbing wall covering various solid angles [or field of view (FOV)] from the listener position as used earlier in [33,34]. For this purpose, a simplistic, highly efficient spatial subsampling method is suggested to map the spatial distribution of reflection coefficients at the shoebox room boundaries to weighting factors for the VRS.…”

Auditory-visual scenes for hearing research

“…Having a virtual acoustic rendering of complex acoustic environments, will allow to specifically manipulate auditory cues to get a better understanding about their relevance. Factors such as conservation of spatial Interaural Time Delay (ITD), Interaural Level Difference (ILD), and Inter Aural Cross Correlation (IACC) cues in binaural hearing aids can be investigated in relevant daily-life settings (e.g., [67,68]). Whereas ITD and ILD cues are relevant for the perceived location of sound sources, IACC influences the perceived width of a sound source.…”