The impact of head-worn devices in an auditory-aided visual search task.

Head-worn devices (HWDs) interfere with the natural transmission of sound from the source to the ears of the listener, worsening their localization abilities. The localization errors introduced by HWDs have been mostly studied in static scenarios, but these errors are reduced if head movements are allowed. We studied the effect of 12 HWDs on an auditory-cued visual search task, where head movements were not restricted. In this task, a visual target had to be identified in a three-dimensional space with the help of an acoustic stimulus emitted from the same location as the visual target. The results showed an increase in the search time caused by the HWDs. Acoustic measurements of a dummy head wearing the studied HWDs showed evidence of impaired localization cues, which were used to estimate the perceived localization errors using computational auditory models of static localization. These models were able to explain the search-time differences in the perceptual task, showing the influence of quadrant errors in the auditory-aided visual search task. These results indicate that HWDs have an impact on sound-source localization even when head movements are possible, which may compromise the safety and the quality of experience of the wearer.

Underwater soundfield visualisation using directionally constrained acoustic parameters.

This paper presents an underwater soundfield visualisation method for passive-sonar applications employing circular hydrophone arrays. The method operates by segregating the space by means of beamforming into angular sectors scanning the whole horizontal plane and then computing acoustic parameters within each sector. The information from these directionally constrained parameters is fused in order to produce spatial spectra which depict the distribution of acoustic energy over bearing. The evaluation is performed on simulated data of circular hydrophone arrays mounted on rigid cylindrical baffles. Comparisons against baseline methods of similar computational complexity suggest that, for moderate to high signal-to-noise ratio levels, the proposed method offers improved performance in terms of background noise suppression, angular resolution, and direction-of-arrival estimation accuracy. Additionally, it is demonstrated that, with the appropriate choice of sector pattern, the proposed method can, at least in some cases, achieve superior performance to the baseline methods in the presence of interferers even at low signal-to-interference ratio levels. Last, the sector-based parameter diffuseness, which is directly related to the direct-to-diffuse ratio, may be used both as a weight function to further attenuate the background noise level and as a confidence measure of the estimation accuracy.

Perceived difficulty of upwind shouting is a misconception explained by convective attenuation effect.

It is a common thought that in windy conditions the voice of a shouter emanates towards the upwind with lower strength than towards the downwind. Contradicting with this, acoustics literature states that a source emanates with a higher amplitude against the upwind direction in comparison with the downwind direction, which is known as the convective amplification or attenuation effect. This article shows that the discrepancy arises because shouters receive their own voice at their ear canals worse when facing against the upwind direction than in the corresponding down-wind case. When shouting upwind, the ears are situated downwind from the mouth, and the strength of one's own voice decreases in the ears due to the convective attenuation effect depending on frequency, making the shouter believe that it is more difficult to shout against the wind. This is shown by computational simulations and real measurements using models of a human shouter with simplified geometries.

The auditory perceived aperture position of the transition between rooms.

This exploratory study investigates the phenomenon of the auditory perceived aperture position (APAP): the point at which one feels they are in the boundary between two adjoined spaces, judged only using auditory senses. The APAP is likely the combined perception of multiple simultaneous auditory cue changes, such as energy, reverberation time, envelopment, decay slope shape, and the direction, amplitude, and colouration of direct and reverberant sound arrivals. A framework for a rendering-free listening test is presented and conducted in situ, avoiding possible inaccuracies from acoustic simulations, impulse response measurements, and auralisation to assess how close the APAP is to the physical aperture position under blindfold conditions, for multiple source positions and two room pairs. Results indicate that the APAP is generally within ± 1 m of the physical aperture position, though reverberation amount, listener orientation, and source position affect precision. Comparison to objective metrics suggests that the APAP generally falls within the period of greatest acoustical change. This study illustrates the non-trivial nature of acoustical room transitions and the detail required for their plausible reproduction in dynamic rendering and game audio engines.

Neural network for multi-exponential sound energy decay analysis.

An established model for sound energy decay functions (EDFs) is the superposition of multiple exponentials and a noise term. This work proposes a neural-network-based approach for estimating the model parameters from EDFs. The network is trained on synthetic EDFs and evaluated on two large datasets of over 20 000 EDF measurements conducted in various acoustic environments. The evaluation shows that the proposed neural network architecture robustly estimates the model parameters from large datasets of measured EDFs while being lightweight and computationally efficient. An implementation of the proposed neural network is publicly available.

Enhancing binaural rendering of head-worn microphone arrays through the use of adaptive spatial covariance matching.

In this article, the application of spatial covariance matching is investigated for the task of producing spatially enhanced binaural signals using head-worn microphone arrays. A two-step processing paradigm is followed, whereby an initial estimate of the binaural signals is first produced using one of three suggested binaural rendering approaches. The proposed spatial covariance matching enhancement is then applied to these estimated binaural signals with the intention of producing refined binaural signals that more closely exhibit the correct spatial cues as dictated by the employed sound-field model and associated spatial parameters. It is demonstrated, through objective and subjective evaluations, that the proposed enhancements in the majority of cases produce binaural signals that more closely resemble the spatial characteristics of simulated reference signals when the enhancement is applied to and compared against the three suggested starting binaural rendering approaches. Furthermore, it is shown that the enhancement produces spatially similar output binaural signals when using these three different approaches, thus indicating that the enhancement is general in nature and could, therefore, be employed to enhance the outputs of other similar binaural rendering algorithms.

Investigating Bilateral Cochlear Implant Users' Localization of Amplitude- and Time-Panned Stimuli Produced Over a Limited Loudspeaker Arrangement.

OBJECTIVE: The objective of this study was to investigate the localization ability of bilateral cochlear implant (BiCI) users for virtual sound sources produced over a limited loudspeaker arrangement. DESIGN: Ten BiCI users and 10 normal-hearing subjects participated in listening tests in which amplitude- and time-panned virtual sound sources were produced over a limited loudspeaker setup with varying azimuth angles. Three stimuli were utilized: speech, bandpassed pink noise between 20 Hz and 1 kHz, and bandpassed pink noise between 1 kHz and 8 kHz. The data were collected via a two-alternative forced-choice procedure and used to calculate the minimum audible angle (MAA) of each subject, which was subsequently compared to the results of previous studies in which real sound sources were employed. RESULT: The median MAAs of the amplitude-panned speech, low-frequency pink noise, and high-frequency pink noise stimuli for the BiCI group were calculated to be 20°, 38°, and 12°, respectively. For the time-panned stimuli, the MAAs of the BiCI group for all three stimuli were calculated to be close to the upper limit of the listening test. CONCLUSIONS: The computed MAAs of the BiCI group for amplitude-panned speech were marginally larger than BiCI users' previously reported MAAs for real sound sources, whereas their computed MAAs for the time-panned stimuli were significantly larger. Subsequent statistical analysis indicated a statistically significant difference in the performances of the BiCI group in localizing the amplitude-panned sources and the time-panned sources. It follows that time-panning over limited loudspeaker arrangements may not be a useful clinical tool, whereas amplitude-panning utilizing such a setup may be further explored as such. Additionally, a comparison with the patient demographics indicated correlations between the results and the patients' age at time of diagnoses and the time passed between date of diagnosis and their implant surgeries.

Spatial post-filter for linear hydrophone arrays with applications to underwater source localisation.

This letter presents a spatial post-filter that can be employed in linear hydrophone arrays, commonly found in sonar systems, for the task of improving the bearing estimation and noise suppression capabilities of traditional beamformers. The proposed filter is computed in the time-frequency domain as the normalised cross-spectral density between two beamformed signals, which are generated by applying conventional beamforming to two adjacent non-overlapping sub-arrays. The evaluation on both simulated and real-world data demonstrates promising performance compared to other popular post-filters in some cases, especially for targets near the end-fire direction and in the presence of uncorrelated interferers or diffuse noise.

Parametric spatial post-filtering utilising high-order circular harmonics with applications to underwater sound-field visualisation.

Beamforming using a circular array of hydrophones may be employed for the task of two-dimensional (2D) underwater sound-field visualisation. In this article, a parametric spatial post-filtering method is proposed, which is specifically intended for applications involving large circular arrays and aims to improve the spatial selectivity of traditional beamformers. In essence, the proposed method is a reformulation of the cross-pattern coherence (CroPaC) spatial post-filter, which involves calculating the normalised cross-spectral density between two signals originating from coincident beamformers. The resulting parameter may be used to sharpen another beamformer steered in the same look-direction, while attenuating ambient noise and interferers from other directions. However, while the original 2D version of the algorithm has been demonstrated to work well with second-order circular harmonic input, it becomes increasingly less suitable with increasing input order. Therefore, the proposed reformulation extends the applicability of CroPaC for much higher orders of circular harmonic input. The method is evaluated with simulated data of a 96-channel circular hydrophone array in three different passive sonar scenarios, where the proposed post-filter is shown to improve the spatial selectivity of both delay-and-sum and minimum-variance distortionless response beamformers.

Superhuman spatial hearing technology for ultrasonic frequencies.

Ultrasonic sources are inaudible to humans, and while digital signal processing techniques are available to bring ultrasonic signals into the audible range, there are currently no systems which also simultaneously permit the listener to localise the sources through spatial hearing. Therefore, we describe a method whereby an in-situ listener with normal binaural hearing can localise ultrasonic sources in real-time; opening-up new applications, such as the monitoring of certain forms of wild life in their habitats and man-made systems. In this work, an array of ultrasonic microphones is mounted to headphones, and the spatial parameters of the ultrasonic sound-field are extracted. A pitch-shifted signal is then rendered to the headphones with spatial properties dictated by the estimated parameters. The processing provides the listener with the spatial cues that would normally occur if the acoustic wave produced by the source were to arrive at the listener having already been pitch-shifted. The results show that the localisation accuracy delivered by the proof-of-concept device implemented here is almost as good as with audible sources, as tested both in the laboratory and under conditions in the field.

Numerical simulations of near-field head-related transfer functions: Magnitude verification and validation with laser spark sources.

Despite possessing an increased perceptual significance, near-field head-related transfer functions (nf-HRTFs) are more difficult to acquire compared to far-field head-related transfer functions. If properly validated, numerical simulations could be employed to estimate nf-HRTFs: the present study aims to validate the usage of wave-based simulations in the near-field. A thorough validation study is designed where various sources of error are investigated and controlled. The present work proposes the usage of a highly-omnidirectional laser-induced breakdown (LIB) of air as an acoustic point source in nf-HRTF measurements. Despite observed departures from the linear regime of the LIB pressure pulse, the validation results show that asymptotically-estimated solutions to a lossless model (wave-equation and rigid boundaries) agree in magnitude with the LIB-measured nf-HRTF of a rigid head replica approximately within 1-2 dB up to about 17 kHz. Except a decreased reliability in notch estimation, no significant shortcoming of the continuous model is found relative to the measurements below 17 kHz. The study also shows the difficulty in obtaining accurate surface boundary impedance values for accurate validation studies.

Machine-learning-based estimation and rendering of scattering in virtual reality.

In this work, a technique to render the acoustic effect of scattering from finite objects in virtual reality is proposed, which aims to provide a perceptually plausible response for the listener, rather than a physically accurate response. The effect is implemented using parametric filter structures and the parameters for the filters are estimated using artificial neural networks. The networks may be trained with modeled or measured data. The input data consist of a set of geometric features describing a large quantity of source-object-receiver configurations, and the target data consist of the filter parameters computed using measured or modeled data. A proof-of-concept implementation is presented, where the geometric descriptions and computationally modeled responses of three-dimensional plate objects are used for training. In a dynamic test scenario, with a single source and plate, the approach is shown to provide a similar spectrogram when compared with a reference case, although some spectral differences remain present. Nevertheless, it is shown with a perceptual test that the technique produces only a slightly lower degree of plausibility than the state-of-the-art acoustic scattering model that accounts for diffraction, and also that the proposed technique yields a prominently higher degree of plausibility than a model that omits diffraction.

The effects of the activation of the inner-hair-cell basolateral K+ channels on auditory nerve responses.

The basolateral membrane of the mammalian inner hair cell (IHC) expresses large voltage and Ca2+ gated outward K+ currents. To quantify how the voltage-dependent activation of the K+ channels affects the functionality of the auditory nerve innervating the IHC, this study adopts a model of mechanical-to-neural transduction in which the basolateral K+ conductances of the IHC can be made voltage-dependent or not. The model shows that the voltage-dependent activation of the K+ channels (i) enhances the phase-locking properties of the auditory fiber (AF) responses; (ii) enables the auditory nerve to encode a large dynamic range of sound levels; (iii) enables the AF responses to synchronize precisely with the envelope of amplitude modulated stimuli; and (iv), is responsible for the steep offset responses of the AFs. These results suggest that the basolateral K+ channels play a major role in determining the well-known response properties of the AFs and challenge the classical view that describes the IHC membrane as an electrical low-pass filter. In contrast to previous models of the IHC-AF complex, this study ascribes many of the AF response properties to fairly basic mechanisms in the IHC membrane rather than to complex mechanisms in the synapse.

Effects of flow gradients on directional radiation of human voice.

In voice communication in windy outdoor conditions, complex velocity gradients appear in the flow field around the source, the receiver, and also in the atmosphere. It is commonly known that voice emanates stronger towards the downstream direction when compared with the upstream direction. In literature, the atmospheric effects are used to explain the stronger emanation in the downstream direction. This work shows that the wind also has an effect to the directivity of voice also favouring the downstream direction. The effect is addressed by measurements and simulations. Laboratory measurements are conducted by using a large pendulum with a loudspeaker mimicking the human head, whereas practical measurements utilizing the human voice are realized by placing a subject through the roof window of a moving car. The measurements and a simulation indicate congruent results in the speech frequency range: When the source faces the downstream direction, stronger radiation coinciding with the wind direction is observed, and when it faces the upstream direction, radiation is not affected notably. The simulated flow gradients show a wake region in the downstream direction, and the simulated acoustic field in the flow show that the region causes a wave-guide effect focusing the sound in the direction.

Model-based estimation of the frequency tuning of the inner-hair-cell stereocilia from neural tuning curves.

This study proposes that the frequency tuning of the inner-hair-cell (IHC) stereocilia in the intact organ of Corti can be derived from the responses of the auditory fibers (AFs) using computational tools. The frequency-dependent relationship between the AF threshold and the amplitude of the stereocilia vibration is estimated using a model of the IHC-mediated mechanical to neural transduction. Depending on the response properties of the considered AF, the amplitude of stereocilia deflection required to drive the simulated AF above threshold is 1.4 to 9.2 dB smaller at low frequencies (≤500 Hz) than at high frequencies (≥4 kHz). The estimated frequency-dependent relationship between ciliary deflection and neural threshold is employed to derive constant-stereocilia-deflection contours from previously published AF recordings from the chinchilla cochlea. This analysis shows that the transduction process partially accounts for the observed differences between the tuning of the basilar membrane and that of the AFs.

Modeling the Perception of Audiovisual Distance: Bayesian Causal Inference and Other Models.

Studies of audiovisual perception of distance are rare. Here, visual and auditory cue interactions in distance are tested against several multisensory models, including a modified causal inference model. In this causal inference model predictions of estimate distributions are included. In our study, the audiovisual perception of distance was overall better explained by Bayesian causal inference than by other traditional models, such as sensory dominance and mandatory integration, and no interaction. Causal inference resolved with probability matching yielded the best fit to the data. Finally, we propose that sensory weights can also be estimated from causal inference. The analysis of the sensory weights allows us to obtain windows within which there is an interaction between the audiovisual stimuli. We find that the visual stimulus always contributes by more than 80% to the perception of visual distance. The visual stimulus also contributes by more than 50% to the perception of auditory distance, but only within a mobile window of interaction, which ranges from 1 to 4 m.

Auditory localization by subjects with unilateral tinnitus.

Tinnitus is associated with changes in neural activity. How such alterations impact the localization ability of subjects with tinnitus remains largely unexplored. In this study, subjects with self-reported unilateral tinnitus were compared to subjects with matching hearing loss at high frequencies and to normal-hearing subjects in horizontal and vertical plane localization tasks. Subjects were asked to localize a pink noise source either alone or over background noise. Results showed some degree of difference between subjects with tinnitus and subjects with normal hearing in horizontal plane localization, which was exacerbated by background noise. However, this difference could be explained by different hearing sensitivities between groups. In vertical plane localization there was no difference between groups in the binaural listening condition, but in monaural listening the tinnitus group localized significantly worse with the tinnitus ear. This effect remained when accounting for differences in hearing sensitivity. It is concluded that tinnitus may degrade auditory localization ability, but this effect is for the most part due to the associated levels of hearing loss. More detailed studies are needed to fully disentangle the effects of hearing loss and tinnitus.

Benefits and applications of laser-induced sparks in real scale model measurements.

The characteristics of using a laser-induced spark as a monopole source in scale model measurements were assessed by comparison with an electric spark and a miniature spherical loudspeaker. Room impulse responses of first order directivity sources were synthesized off-line using six spatially distributed sparks. The source steering direction was scanned across the horizontal and vertical plane to assess the origin of early reflections. The results confirm that the characteristics of the laser-induced spark outperform those of typical sources. Its monopole characteristics enable the authors to synthesize room responses of directional sources, e.g., to obtain directional information about reflections inside scale models.

Neural realignment of spatially separated sound components.

Natural auditory scenes often consist of several sound sources overlapping in time, but separated in space. Yet, location is not fully exploited in auditory grouping: spatially separated sounds can get perceptually fused into a single auditory object and this leads to difficulties in the identification and localization of concurrent sounds. Here, the brain mechanisms responsible for grouping across spatial locations were explored in magnetoencephalography (MEG) recordings. The results show that the cortical representation of a vowel spatially separated into two locations reflects the perceived location of the speech sound rather than the physical locations of the individual components. In other words, the auditory scene is neurally rearranged to bring components into spatial alignment when they were deemed to belong to the same object. This renders the original spatial information unavailable at the level of the auditory cortex and may contribute to difficulties in concurrent sound segregation.

Beamforming with a volumetric array of massless laser spark sources--Application in reflection tracking.

A volumetric array of laser-induced air breakdown sparks is used to produce a directional and steerable acoustic source. The laser breakdown array element is broadband, point-like, and massless. It produces an impulse-like waveform in midair, thus generating accurate spatio-temporal information for acoustic beamforming. A laser-spark scanning setup and the concept of a massless steerable source are presented and evaluated with a cubic array by using an off-line far field delay-and-sum beamforming method. This virtual acoustic array with minimal source influence can, for instance, produce narrow transmission beams to obtain localized and directional impulse response information by reflection tracking.