Gregory Reardon

Gregory Reardon

Ph.D. Candidate at University of California, Santa Barbara

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A list of all the posts and pages found on the site. For you robots out there is an XML version available for digesting as well.

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Evaluation of Binaural Renderers: A Methodology

Published in AES Convention 143, 1900

Recent developments in immersive audio technology have motivated a proliferation of binaural renderers used for creating spatial audio content. Binaural renderers leverage psychoacoustic features of human hearing to reproduce a 3D sound image over headphones. In this paper a methodology for the comparative evaluation of different binaural renderers is presented. The methodological approach is threefold. A subjective evaluation of 1) quantitative characteristics (such as front/back and up/down discrimination, localization); 2) qualitative characteristics (such as timbre, naturalness); and 3) overall preference. The main objective of the methodology is to help to elucidate the most meaningful factors for the performance of binaural renderers and to provide indications on possible improvements in the rendering process.

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Evaluation of Binaural Renderers: Externalization

Published in AES Convention 144, 1900

Binaural renderers can be used to reproduce dynamic spatial audio over headphones and deliver immersive audio content. Six commercially available binaural renderers with different rendering methodologies were evaluated in a multi-phase subjective study. This paper presents and discusses the testing methodology, evaluation criteria, and main findings of the externalization, front/back discrimination and up/down discrimination tasks that are part of the first phase. Statistical analysis over a large number of subjects revealed that the choice of renderer has a significant effect on all three dependent measures. Further, ratings of perceived externalization for the renderers were found to be content-specific, while renderer reversal rates were much more robust to different stimuli.

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Evaluation of Binaural Renderers: Localization

Published in AES Convention 144, 1900

Binaural renderers can be used to reproduce spatial audio over headphones. A number of different renderers have recently become commercially available for use in creating immersive audio content. High-quality spatial audio can be used to significantly enhance experiences in a number of different media applications, such as virtual, mixed and augmented reality, computer games, and music and movie. A large multi-phase experiment evaluating six commercial binaural renderers was performed. This paper presents the methodology, evaluation criteria, and main findings of the horizontal-plane source localization experiment carried out with these renderers. Significant differences between renderers’ regional localization accuracy were found. Consistent with previous research, subjects tended to localize better in the front and back of the head than at the sides. Differences between renderer performance at the side regions heavily contributed to their overall regional localization accuracy.

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Evaluation of Binaural Renderers: Multidimensional Sound Quality Assessment

Published in AES International Conference on Audio for Virtual and Augmented Reality, 1900

A multi-phase subjective experiment evaluating six commercially available binaural audio renderers was carried out. This paper presents the methodology, evaluation criteria, and main findings of the tests that assessed perceived sound quality of the renderers. Subjects appraised a number of specific sound quality attributes—timbral balance, clarity, naturalness, spaciousness, and dialogue intelligibility—and ranked, in terms of preference, the renderers for a set of music and movie stimuli presented over headphones. Results indicated that differences between the perceived quality and preference for a renderer are discernible. Binaural renderer performance was also found to be highly content-dependent, with significant interactions between renderers and individual stimuli being found, making it difficult to determine an “optimal” renderer for all settings.

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Acoustic Perturbations in HRTFs Measured on Mixed Reality Headsets

Published in AES International Conference on Audio for Virtual and Augmented Reality, 1900

Materials that obstruct the path of acoustic waveforms in free-field to the human ear, may introduce distortions that can modify the natural Head-Related Transfer Functions. In this paper the effect of wearing commercially available Head-Mounted Displays for Mixed and Augmented Reality has been measured via a dummy head mannequin. Such spectral distortions may be relevant for mixed reality environments where real and virtual sounds mix together in the same auditory scene. The analysis revealed that the measured HMDs affected the fine structure of the HRTF (> 3–6 kHz) and also introduced non-negligible distortions in the interaural level difference range mostly at the contralateral ear. Distortion patterns in HRTFs and cue modi?cations are reported and discussed across incidence angles and frequency bands.

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Cutaneous Wave Propagation Shapes Tactile Motion: Evidence from Air-Coupled Ultrasound

Published in IEEE World Haptics Conference, 1900

Tactile stimulation of the skin excites cutaneous waves that travel tens of centimeters, but the implications for haptic engineering and perception are not well understood. We present evidence from optical vibrometry that tactile motion cues delivered via air-coupled ultrasound excite complex spatiotemporal wave fields in the hand. We distinguished two physical regimes based on the ratio of the motion speed to the cutaneous wave speed. At low speeds (1-4 m/s), waves generated by a moving stimulus propagated to similar distances in all directions. At high speeds (4-15 m/s), waves in the direction of motion were compressed. We also studied tactile motion perception at these speeds, which were faster than those used in prior studies. Motion sensitivity was impaired when waves were inhibited in front of the moving stimulus. This occurred for motion at high speeds and across disconnected skin areas. Together, our findings suggest that tactile motion perception is aided by waves propagating in the skin. This paper presents the first time-resolved observations of cutaneous responses to focused ultrasound, and contributes practical knowledge for the use of tactile motion and mid-air haptic feedback.

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Ferrofluid Electromagnetic Actuators for High-Fidelity Haptic Feedback

Published in Sensory and Actuators A: Physical, 1900

Engineering high-fidelity haptic actuators is challenging due to the impressive tactile sensing characteristics of human skin, which possesses a wide frequency bandwidth, high spatial and temporal resolution, and large dynamic range. These attributes cannot be matched by existing haptic feedback technologies. Efficient, compact electromagnetic haptic actuators are needed in many emerging haptic systems, but their bandwidth and dynamic range are fundamentally constrained by heat transfer effects that become extremely limiting as device dimensions are decreased. Here, we present a compact actuator for delivering high-fidelity haptic feedback via an electromagnetic assembly comprising a magnetically-driven fabric-reinforced elastic membrane coupled to a ferrofluid encapsulated magnetic circuit. Using theoretical modeling, simulations, and experiments, we show how the mechanical design, magnetic circuit, and thermal design of this fingertip-sized actuator enable it to deliver sustained forces or indentations, wide-bandwidth vibrations, sustained forces of 3 Newtons, transient forces exceeding 13 Newtons. These actuators can be leveraged to supply many emerging systems and products with high fidelity haptic feedback.

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Shear Shock Waves Mediate Haptic Holography via Focused Ultrasound

Published in Science Advances, 1900

Emerging holographic haptic interfaces focus ultrasound in air to enable their users to touch, feel, and manipulate three-dimensional virtual objects. However, current holographic haptic systems furnish tactile sensations that are diffuse and faint, with apparent spatial resolutions that are far coarser than would be theoretically predicted from acoustic focusing. Here, we show how the effective spatial resolution and dynamic range of holographic haptic displays are determined by ultrasound-driven elastic wave transport in soft tissues. Using time-resolved optical imaging and numerical simulations, we show that ultrasound-based holographic displays excite shear shock wave patterns in the skin. The spatial dimensions of these wave patterns can exceed nominal focal dimensions by more than an order of magnitude. Analyses of data from behavioral and vibrometry experiments indicate that shock formation diminishes perceptual acuity. For holographic haptic displays to attain their potential, techniques for circumventing shock wave artifacts, or for exploiting these phenomena, are needed.

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Dynamic Feedback in Wave-Mediated Surface Haptics: A Modular Platform

Published in IEEE World Haptics Conference, 1900

Emerging surface haptic technologies exploit wave physics to create software-programmable two-dimensional haptic displays. However, designing such systems is challenging due to the complex dependence of wave propagation on the system’s hardware arrangement, materials, and boundary conditions. We present a modular system for exploring design opportunities for wave-mediated haptic feedback via elastic surfaces. The system integrates an array of repositionable, custom electromagnetic actuators that excite shear waves which propagate in a reconfigurable elastic medium. We use optical vibrometry imaging to capture data that fully encode the transmission of waves in this system. We present methods that leverage the linearity of wave transport and the acquired data to efficiently implement and evaluate a variety of hardware configurations and software methods for displaying dynamic, spatially-resolved two-dimensional haptic feedback. These techniques can allow researchers to rapidly investigate methods for engineering software-programmable surface haptic displays based on wave excitation.

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