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Abstract Audio augmented reality (AAR), a prominent topic in the field of audio, requires understanding the listening environment of the user for rendering an authentic virtual auditory object. Reverberation time ( $$RT_{60}$$ R T 60 ) is a predominant metric for the characterization of room acoustics and numerous approaches have been proposed to estimate it blindly from a reverberant speech signal. However, a single $$RT_{60}$$ R T 60 value may not be sufficient to correctly describe and render the acoustics of a room. This contribution presents a method for the estimation of multiple room acoustic parameters required to render close-to-accurate room acoustics in an unknown environment. It is shown how these parameters can be estimated blindly using an audio transformer that can be deployed on a mobile device. Furthermore, the paper also discusses the use of the estimated room acoustic parameters to find a similar room from a dataset of real BRIRs that can be further used for rendering the virtual audio source. Additionally, a novel binaural room impulse response (BRIR) augmentation technique to overcome the limitation of inadequate data is proposed. Finally, the proposed method is validated perceptually by means of a listening test.

Abstract High-quality rendering of spatial sound fields in real-time is becoming increasingly important with the steadily growing interest in virtual and augmented reality technologies. Typically, a spherical microphone array (SMA) is used to capture a spatial sound field. The captured sound field can be reproduced over headphones in real-time using binaural rendering, virtually placing a single listener in the sound field. Common methods for binaural rendering first spatially encode the sound field by transforming it to the spherical harmonics domain and then decode the sound field binaurally by combining it with head-related transfer functions (HRTFs). However, these rendering methods are computationally demanding, especially for high-order SMAs, and require implementing quite sophisticated real-time signal processing. This paper presents a computationally more efficient method for real-time binaural rendering of SMA signals by linear filtering. The proposed method allows representing any common rendering chain as a set of precomputed finite impulse response filters, which are then applied to the SMA signals in real-time using fast convolution to produce the binaural signals. Results of the technical evaluation show that the presented approach is equivalent to conventional rendering methods while being computationally less demanding and easier to implement using any real-time convolution system. However, the lower computational complexity goes along with lower flexibility. On the one hand, encoding and decoding are no longer decoupled, and on the other hand, sound field transformations in the SH domain can no longer be performed. Consequently, in the proposed method, a filter set must be precomputed and stored for each possible head orientation of the listener, leading to higher memory requirements than the conventional methods. As such, the approach is particularly well suited for efficient real-time binaural rendering of SMA signals in a fixed setup where usually a limited range of head orientations is sufficient, such as live concert streaming or VR teleconferencing.

The latest MPEG standard, MPEG-H 3D Audio, employs the virtual loudspeaker rendering (VLR) technique to support virtual reality (VR) and augmented reality (AR). During the rendering, the binaural downmixing of channel signals often induces the so-called comb filter effect, an undesirable spectral artifact, due to the phase difference between the binaural filters. In this paper, we propose an efficient algorithm that can mitigate such spectral artifacts. The proposed algorithm performs spectral compensation in both the panning gain and downmix signal domains depending on the frequency range. In the low-frequency bands where a band has a wider bandwidth than the critical-frequency scale, panning gains are directly compensated. In the high-frequency bands, where a band has a narrower bandwidth than the critical-frequency scale, a signal compensation similar to the active downmix is performed. As a result, the proposed algorithm optimizes the performance and the complexity within MPEG-H 3DA framework. By implementing the algorithm on MPEG-H 3DA BR, we verify that the additional computation complexity is minor. We also show that the proposed algorithm improves the subjective quality of MPEG-H 3DA BR significantly. [ABSTRACT FROM AUTHOR]

Individual Head-Related Transfer Functions (HRTFs) are necessary for the accurate rendering of virtual scenes. However, their acquisition is challenging given the complex pinna shape. Numerical methods can be leveraged to compute HRTFs on meshes originating from precise scans of a subject. Although photogrammetry can be used for the scanning, its inaccuracy might affect the spatial cues of simulated HRTFs. This paper aims to assess the significance of the photogrammetric error affecting a Neumann KU100 dummy head scan. The geometrical differences between the photogrammetric scan and a laser scan are mainly located at the pinna cavities. The computed photogrammetric HRTFs, compared to measured and simulated data using objective and perceptually inspired metrics, show deviation in high frequency spectral features, stemming from the photogrammetric scanning error. This spectral deviation hinders the modelled elevation perception with photogrammetric HRTFs to levels comparable to renderings with nonindividual data. Extracting the photogrammetric geometry at individual ear cavities and merging it to the laser mesh, an assessment of the influence of the inaccuracy at different pinna structures is conducted. Correlation analysis between acoustic and geometrical metrics computed on the results is used to identify the most relevant geometrical metrics in relation to the HRTFs.

High-quality rendering of spatial sound fields in real-time is becoming increasingly important with the steadily growing interest in virtual and augmented reality technologies. Typically, a spherical microphone array (SMA) is used to capture a spatial sound field. The captured sound field can be reproduced over headphones in real-time using binaural rendering, virtually placing a single listener in the sound field. Common methods for binaural rendering first spatially encode the sound field by transforming it to the spherical harmonics domain and then decode the sound field binaurally by combining it with head-related transfer functions (HRTFs). However, these rendering methods are computationally demanding, especially for high-order SMAs, and require implementing quite sophisticated real-time signal processing. This paper presents a computationally more efficient method for real-time binaural rendering of SMA signals by linear filtering. The proposed method allows representing any common rendering chain as a set of precomputed finite impulse response filters, which are then applied to the SMA signals in real-time using fast convolution to produce the binaural signals. Results of the technical evaluation show that the presented approach is equivalent to conventional rendering methods while being computationally less demanding and easier to implement using any real-time convolution system. However, the lower computational complexity goes along with lower flexibility. On the one hand, encoding and decoding are no longer decoupled, and on the other hand, sound field transformations in the SH domain can no longer be performed. Consequently, in the proposed method, a filter set must be precomputed and stored for each possible head orientation of the listener, leading to higher memory requirements than the conventional methods. As such, the approach is particularly well suited for efficient real-time binaural rendering of SMA signals in a fixed setup where usually a limited range of head orientations is sufficient, such as live concert streaming or VR teleconferencing. [ABSTRACT FROM AUTHOR]

In dynamic virtual reality, visual cues and motor actions aid auditory perception. With multimodal integration and auditory adaptation effects, generic head-related transfer functions (HRTFs) may yield no significant disadvantage to individual HRTFs regarding accurate auditory perception. This study compares two individual HRTF sets against a generic HRTF set by way of objective analysis and two subjective experiments. First, auditory-model-based predictions examine the objective deviations in localization cues between the sets. Next, the HRTFs are compared in a static subjective ( N = 8 ) localization experiment. Finally, the localization accuracy, timbre, and overall quality of the HRTF sets are evaluated subjectively ( N = 12 ) in a six-degrees-of-freedom audio-visual virtual environment. The results show statistically significant objective deviations between the sets, but no perceived localization or overall quality differences in the dynamic virtual reality. [ABSTRACT FROM AUTHOR]

Binaural rendering of Ambisonics signals is a common way to reproduce spatial audio content. Processing Ambisonics signals at low spatial orders is desirable in order to reduce complexity, although it may degrade the perceived quality, in part due to the mismatch that occurs when a low-order Ambisonics signal is paired with a spatially dense head-related transfer function (HRTF). In order to alleviate this issue, the HRTF may be preprocessed so its spatial order is reduced. Several preprocessing methods have been proposed, but they have not been thoroughly compared yet. In this study, nine HRTF preprocessing methods were used to render anechoic binaural signals from Ambisonics representations of orders 1 to 44, and these were compared through perceptual hearing models in terms of localisation performance, externalisation and speech reception. This assessment was supported by numerical analyses of HRTF interpolation errors, interaural differences, perceptually-relevant spectral differences, and loudness stability. Models predicted that the binaural renderings’ accuracy increased with spatial order, as expected. A notable effect of the preprocessing method was observed: whereas all methods performed similarly at the highest spatial orders, some were considerably better at lower orders. A newly proposed method, BiMagLS, displayed the best performance overall and is recommended for the rendering of bilateral Ambisonics signals. The results, which were in line with previous literature, indirectly validate the perceptual models’ ability to predict listeners’ responses in a consistent and explicable manner.

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In dynamic virtual reality, visual cues and motor actions aid auditory perception. With multimodal integration and auditory adaptation effects, generic head-related transfer functions (HRTFs) may yield no significant disadvantage to individual HRTFs regarding accurate auditory perception. This study compares two individual HRTF sets against a generic HRTF set by way of objective analysis and two subjective experiments. First, auditory-model-based predictions examine the objective deviations in localization cues between the sets. Next, the HRTFs are compared in a static subjective (N=8) localization experiment. Finally, the localization accuracy, timbre, and overall quality of the HRTF sets are evaluated subjectively (N=12) in a six-degrees-of-freedom audio-visual virtual environment. The results show statistically significant objective deviations between the sets, but no perceived localization or overall quality differences in the dynamic virtual reality.

It is commonly believed that near-field head-related transfer functions (HRTFs) provide perceptual benefits over far-field HRTFs that enhance the plausibility of binaural rendering of nearby sound sources. However, to the best of our knowledge, no study has systematically investigated whether using near-field HRTFs actually provides a perceptually more plausible virtual acoustic environment. To assess this question, we conducted two experiments in a six-degrees-of-freedom multimodal augmented reality experience where participants had to compare non-individual anechoic binaural renderings based on either synthesized near-field HRTFs or intensity-scaled far-field HRTFs and judge which of the two rendering methods led to a more plausible representation. Participants controlled the virtual sound source position by moving a small handheld loudspeaker along a prescribed trajectory laterally and frontally near the head, which provided visual and proprioceptive cues in addition to the auditory cues. The results of both experiments show no evidence that near-field cues enhance the plausibility of non-individual binaural rendering of nearby anechoic sound sources in a dynamic multimodal virtual acoustic scene as examined in this study. These findings suggest that, at least in terms of plausibility, the additional effort of including near-field cues in binaural rendering may not always be worthwhile for virtual or augmented reality applications.

In this article, a systematic overview of various recording and reproduction techniques for spatial audio is presented. While binaural recording and rendering is designed to resemble the human two-ear auditory system and reproduce sounds specifically for a listener's two ears, soundfield recording and reproduction using a large number of microphones and loudspeakers replicate an acoustic scene within a region. These two fundamentally different types of techniques are discussed in the paper. A recent popular area, multi-zone reproduction, is also briefly reviewed in the paper. The paper is concluded with a discussion of the current state of the field and open problems. [ABSTRACT FROM AUTHOR]

To provide immersive 3D multimedia service, MPEG has launched MPEG-H, ISO/IEC 23008, “High Efficiency Coding and Media Delivery in Heterogeneous Environments.” As part of the audio, MPEG-H 3D Audio has been standardized based on a multichannel loudspeaker configuration (e.g., 22.2). Binaural rendering is a key application of 3D audio; however, previous studies focus on binaural rendering with low complexity such as IIR filter design for HRTF or pre-/post-processing to solve in-head localization or front-back confusion. In this paper, a new binaural rendering algorithm is proposed to support the large number of input channel signals and provide high-quality in terms of timbre, parts of this algorithm were adopted into the MPEG-H 3D Audio. The proposed algorithm truncates binaural room impulse response at mixing time, the transition point from the early-reflections to the late reverberation part. Each part is processed independently by variable order filtering in frequency domain (VOFF) and parametric late reverberation filtering (PLF), respectively. Further, a QMF domain tapped delay line (QTDL) is proposed to reduce complexity in the high-frequency band, based on human auditory perception and codec characteristics. In the proposed algorithm, a scalability scheme is adopted to cover a wide range of applications by adjusting the threshold of mixing time. Experimental results show that the proposed algorithm is able to provide the audio quality of a binaural rendered signal using full-length binaural room impulse responses. A scalability test also shows that the proposed scalability scheme smoothly compromises between audio quality and computational complexity. [ABSTRACT FROM PUBLISHER]

This paper presents a new binaural auralization algorithm suitable for mobile devices. A stereo-tomultichannel virtual upmix technique was utilized to expand the spatial dimension of stereo audio to a multichannel speaker space. In order to enhance subjective preferences and listener envelopment, reflections of the primary sound component were artificially generated by modeling a virtual ceiling and sidewalls based on concert hall acoustics. The uncorrelated ambient components were then distributed over spatial points at different azimuth and elevation angles. Computational efficiency was achieved by removing the redundant operations in each stage of the algorithm. Subjective tests were performed, and the results showed that the proposed algorithm significantly improves spatial perceptions of stereo audio being played over headphones. [ABSTRACT FROM AUTHOR]