Perceptual Evaluation of Mitigation Approaches of Impairments due to Spatial Undersampling in Binaural Rendering of Spherical Microphone Array Data

Abstract

Spherical microphone arrays (SMAs) are widely used to capture spatial sound fields that can then be rendered in various ways as a virtual acoustic environment (VAE) including headphone-based binaural synthesis. Several practical limitations have a significant impact on the fidelity of the rendered VAE. The finite number of microphones of SMAs leads to spatial undersampling of the captured sound field, which, on the one hand, induces spatial aliasing artifacts and, on the other hand, limits the order of the spherical harmonics (SH) representation. Several approaches have been presented in the literature that aim to mitigate the perceptual impairments due to these limitations. In this article, we present a listening experiment evaluating the perceptual improvements of binaural rendering of undersampled SMA data that can be achieved using state-of-the-art mitigation approaches. In particular, we examined the Magnitude Least-Squares algorithm, the Bandwidth Extraction Algorithm for Microphone Arrays, Spherical Head Filters, SH Tapering, and a newly proposed equalization filter. In the experiment, subjects rated the perceived differences between a dummy head and the corresponding SMA auralization. We found that most mitigation approaches lead to significant perceptual improvements, even though audible differences to the reference remain.

Binaural Reproduction Based on Bilateral Ambisonics and Ear-Aligned HRTFs

“…Although the linear-phase component at high frequencies may be less important for lateral localization [26], [27], its removal still introduces errors in the binaural signal, and may affect other perceptual attributes [28], [29]. In [30], Lübeck et al showed that the MagLS method achieved similar perceptual improvement to the equalization methods for binaural reproduction with order 3 and above. In summary, despite of the significant advance in this field, current methods for binaural reproduction that are based on low-order HRTF and sound-field representations seem to degrade perception compared to a high-order reference.…”

The Far-Field Equatorial Array for Binaural Rendering

“…Despite the limitations of the scattering removal, the available data suggest that the presented approach produces a lower error for horizontally propagating sound fields compared to the cylindrical array from [14], which was composed of multiple circular rings of microphones with total number of microphones that was equal to a conventional spherical array of the same SH order. The circumstance that typical arrays are generally not capable of capturing the sound field accurately at high frequencies has been shown to be tolerable particularly when binaural rendering is the targeted application [28].…”

Binaural Auralization of Microphone Array Room Impulse Responses Using Causal Wiener Filtering

“…Fig. 5 shows the NMSE according to (22) for several filter designs with different levels of regularization, obtained by varying the modeled microphone signal SNR (given by 1/σ 2 v ). The general trend is that the MSE increases towards high frequencies where microphone array spatial aliasing, increasingly complex HRTF beam patterns, and a limited number of microphone channels prevent accurate synthesis of the target beam pattern.…”

“…Approaches have been developed to mitigate the effects of limited SH-order on binaural rendering [22]. One approach mentioned in [22] is pre-processing of the HRTF target responses, which can reduce the SH-order needed to represent the HRTFs without giving perceptual consequences [23] [24] (this idea could also be applied to our case of direct binaural signal estimation and is a possibility for future research).…”

“…Approaches have been developed to mitigate the effects of limited SH-order on binaural rendering [22]. One approach mentioned in [22] is pre-processing of the HRTF target responses, which can reduce the SH-order needed to represent the HRTFs without giving perceptual consequences [23] [24] (this idea could also be applied to our case of direct binaural signal estimation and is a possibility for future research). However, there is no evidence presented in the cited articles that HRTFs can be simplified in a perceptually transparent way, for all directions and all frequencies, to enable modeling of direct sound at a SH-order down to three, which is the maximum of the SMA employed in our application example.…”