bluuebunny/crossref_metadata_2025 huggingface dataset:
Cramer Rao lower bound for two-dimensional elastotography
Authors: Verma Prashant , Doyley Marvin M.
Published: June 2017

In this study, we present a theoretical framework for characterizing the performance of two-dimensional displacement and strain estimators. Specifically, we derived the Cramer-Rao lower bound for axial and lateral displacements estimated from radio frequency echo data. The derived analytical expressions include the effects of signal decorrelation, electronic noise, point spread function (PSF), and signal processing parameters (window size and overlap between the successive windows). We modeled the 2-D PSF of pulse-echo imaging system as a sinc-modulated spatial sine pulse in the axial direction and as a sinc function in the lateral direction. For validation, we compared the variance in displacements and strains, incurred when quasi-static elastography was performed using conventional linear array (CLA), plane wave (PW) and compounded plane wave (CPW) imaging techniques. We also extended the theory to assess the performance of vascular elastograms. The modified analytical expressions predicted that CLA and CPW should provide the worst and best elastographic performance, respectively, which was confirmed both in simulations and experimental studies. Additionally, our framework predicted that the peak performance should occur when 2 \% strain is applied, the same order of magnitude as observed in simulations (1 \%) and experiments (1 \% -- 2 \%).
Using frequency-sum beamforming in passive cavitation imaging
Authors: Abadi Shima , Haworth Kevin J. , Mercado Karla P. , Dowling David R.
Published: June 2017

Passive Cavitation Imaging (PCI) is a method for locating cavitation emissions to study biological effects of ultrasound on tissues. In this method, an image is formed by beamforming passively recorded acoustic emissions with an array. The image resolution depends on the ultrasound frequency and array geometry. Acoustic emissions can be scattered due to tissue inhomogeneity, which may degrade the image resolution. Emissions at higher frequencies are more susceptible to such degradation. Frequency-sum beamforming is a nonlinear technique that alters this sensitivity to scattering by manufacturing higher frequency information from lower frequency components via a quadratic product of complex signal amplitudes. This presentation evaluates the performance of frequency-sum beamforming in a scattering environment using simulations and experiments, conducted in the kHz and MHz frequency regimes. First, 50 and 100 kHz signals were broadcasted from a single source to an array of 16 hydrophones in a water tank with and without discrete scatterers. Second, a tissue-mimicking phantom perfused with microbubbles was insonified at 2 MHz, and the emissions were received by a 128-element linear array. The performance of frequency-sum beamforming was compared to conventional delay-and-sum and minimum variance beamforming in mild and strong scattering environments. [Work partially supported by NAVSEA through the NEEC.]
Hybrid silencer transmission loss above a duct’s plane wave region
Authors: Williams Paul T. , Åbom Mats , Kirby Ray , Hill James
Published: June 2017

For large ducts, the removal of low frequency and tonal noise is normally achieved through the use of inefficient dissipative silencers; however, a combination of dissipative and reactive solutions could be more effective. But reactive noise control solutions are rarely applied to large diameter duct systems since it is commonly assumed that the low cut-on frequency of higher order modes severely restricts their efficiency. However, it is possible for a reactive silencer to remain operational outside of the plane wave region, provided the reactive elements are distributed across the cross-section of the duct. Of course, at higher frequencies, the sound field within a duct will have nonplane wave modal content, and the transmission loss is expected to differ compared to the plane wave condition. This effect is investigated here using numerical (FEM) predictions for hybrid dissipative-reactive parallel baffle silencers and the performance of the reactive elements is explored under different excitations. The effects of non-planar fields and individually excited modes are analyzed, and it is found that the frequency range over which quarter wave resonators contribute to transmission loss can be extended above the cut-on frequency of the duct by increasing the number of baffles.
Stop whistling! A note on fluid driven whistles in flow ducts
Authors: Karlsson Mikael , Knutsson Magnus , Åbom Mats
Published: June 2017

The generation mechanism and possible counter measures for fluid driven whistles in low Mach number flow duct networks are discussed. The vortex sound model, where unstable shear layers interact with the acoustic field and act as amplifiers under certain boundary conditions, is shown to capture the physics well. Further, for the system to actually whistle, an acoustic feedback to the amplifying shear layer is also needed. The demonstration example in this study is a generalized resonator configuration with annular volumes attached to a straight flow duct via a number of small holes, perforations, around the duct’s circumference. At each hole, a shear layer is formed and the acoustic reflections from the resonator volumes and the up and downstream sides provides a possible feedback to them. The attenuation properties as well as the whistling frequencies at varying inlet mean flow velocities for this system are studied both numerically and experimentally showing that good quality predictive simulations are possible using the vortex sound theory. Finally, a few countermeasures against whistling are tested. Both the feedback and the shear layers are manipulated. Best effect was found disturbing the shear layers by covering the holes with a coarse mesh.
Comparison of an integral and a collocation based impedance-to-scattering matrix methods for large silencers analysis
Authors: Wang Peng , Zhou Limin , Wu T. W.
Published: June 2017

Large silencers used in power generation industry usually have a large cross section at the inlet/outlet. The plane-wave cutoff frequency of the inlet/outlet duct could be below only a few hundred Hz. To evaluate the acoustical performance of large silencers above the inlet/outlet cutoff, either an integral based or a point-collocation based impedance-to-scattering matrix method may be applied to convert the BEM impedance matrix to the scattering matrix with the higher-order modes at the inlet/outlet. In this presentation, these two impedance-to-scattering matrix methods are introduced first, and then several test cases are used to compare the computational accuracy, efficiency, and stability of the two methods.
Reduced vessel tone leads to vasodilation and decreased cerebral rigidity
Authors: Schregel Katharina , Palotai Miklos , Nazari Navid , Barbone Paul E. , Sinkus Ralph , Patz Samuel
Published: June 2017

Magnetic Resonance Elastography (MRE) measures elastic shear wave propagation in vivo to infer biomechanical properties non-invasively [Muthupillai, et al. (1995) Science;269:1854-1857.]. Models predict that tissue stiffness is influenced by changes of vascular properties [Parker, et al. (2016) PhysMedBiol;61:4890-4903.]. Cerebral blood supply is closely regulated by diameter changes of blood vessels. We here investigated the influence of vasodilation on cerebral brain stiffness with MRE. A healthy C57BL/6 mouse was anesthetized with isoflurane mixed in 100% O2. Vasodilation was induced by a hypercapnic challenge (isoflurane mixed in 95% O2 + 5% CO2). Brain stiffness was measured with a 3D spin-echo MRE sequence in a 7T animal MRI scanner under normocapnic and hypercapnic conditions. Vibration frequency was 1 kHz. Wave length and wave speed was observed to decrease significantly under hypercapnic conditions across the whole brain when compared to baseline. These changes correspond to a decrease in tissue rigidity. We conclude, therefore, that vasodilation via reducing vessel tone leads to a significant decrease in brain rigidity. Therefore, potential changes in cerebral blood flow due to physiological or pathological conditions should be considered when studying brain rigidity.
Breaking the barriers of temporal and spatial resolutions for ultrasound neuroimaging
Authors: Tanter Mickael
Published: June 2017

The introduction of plane or diverging wave transmissions rather than line by line scanning focused beams has broken the conventional barriers of ultrasound imaging. The frame rate reaches the theoretical limit of physics dictated by the ultrasound speed and an ultrasonic map can be provided typically in tens of micro-seconds (thousands of frames per second). Interestingly, this leap in frame rate is not only a technological breakthrough, but it permits the advent of completely new ultrasound imaging modes, in particular, neuro-functional ultrasound imaging of brain activity (fUltrasound). Indeed, ultrafast Doppler gives ultrasound the ability to detect very subtle blood flow in small vessels and paves the way for fUltrasound of brain activity through the neurovascular coupling. It provides the first modality for whole brain imaging on awake and freely moving animals with unprecedented resolutions1,2,3 compared to fMRI. Finally, we demonstrated that it can be combined with 3 µm diameter microbubbles injections to provide a first in vivo and non-invasive imaging modality at microscopic scales deep into organs by localizing the position of millions of microbubbles at ultrafast frame rates. This ultrasound localization microscopy technique solves for the first time the problem of in vivo imaging the whole brain microvasculature 4. 1. Mace et al., Nature Methods 2011. 2. Osmanski et al., Nature Commun. 2014. 3. Sieu et al., Nature Methods 2015. 4. Errico et al., Nature 2015.
Traveling wave control of stringed musical instruments
Authors: Donovan Liam , McPherson Andrew
Published: June 2017

Traveling wave control is a technique in which the energy propagating around a structure in the form of waves can be manipulated directly in order to change the overall dynamic behaviour of the structure. In this research, traveling wave control is applied to a musical instrument string with a view to affecting the timbre of the sounds produced by the string when vibrating. A highly linear custom optical sensor is built which is capable of detecting a wave traveling on a string in a single direction, and a piezo stack actuator is situated under the termination point of the string allowing the reflection of the wave to be manipulated directly. Various controllers are analyzed theoretically in terms of their performance, stability, and musical usefulness. They are then implemented and evaluated in terms of their relevance to the design of new musical instruments.
Monitoring saxophone reed vibrations using a piezoelectric sensor
Authors: Hofmann Alex , Chatziioannou Vasileios , Mayer Alexander , Hartmann Harry
Published: June 2017

In sound production on single-reed woodwind instruments the reed is oscillating in a frequency related to the length of the resonator. Strain gauge sensors attached to single reeds have been used to capture the vibrations of the reed to investigate articulation techniques on saxophone and clarinet. Reeds can be made from natural cane and also from synthetic materials like oriented polymers or layers of fiber-reinforced polymers. Such synthetic reeds allow to integrate sensors inside the reed during manufacture. However, integrated strain gauge sensors produced signals with high noise, which have been shown not to be ideal for amplification purposes. Replacing the integrated strain gauge with a piezo film sensor greatly enhanced the sound quality of the sensor reeds. With this procedure, electronically augmented woodwind instruments may be constructed for performance, acoustic measurements, and music pedagogy feedback systems.
Development of a hybrid wind instrument—Some key findings
Authors: Buys Kurijn , Sharp David , Laney Robin
Published: June 2017

A hybrid wind instrument is constructed by putting a theoretical excitation model (such as a real-time computed physical model of a clarinet embouchure) in interaction with a real wind instrument resonator. In previous work, the successful construction of a hybrid wind instrument has been demonstrated, with the interaction facilitated by a loudspeaker and a microphone placed at the entrance of a clarinet-like tube. The present paper focuses on some key findings, concentrating particularly on the “musical instrument” and “research tool” perspectives. The limitations of the hybrid set-up are considered. In particular, the choice of the loudspeaker used in the set-up is explained and the occurrence (and prevention) of instabilities during the operation of the hybrid instrument are discussed. For the design of excitation models used to drive the hybrid instrument, the usefulness of dimensionless and reduced parameter forms is outlined. In contrast to previously reported physically based excitation models, it is demonstrated that a purely mathematical “polynomial model” enables an independent control of separate sound features. For all excitation models, the sounds produced with the hybrid instrument are shown to match to those predicted by simulation. However, the hybrid instrument is more easily destabilized for certain extreme parameter states.
A perception-based protocol for the systematic selection of urban sites with specific soundscapes
Authors: De Coensel Bert , Botteldooren Dick
Published: June 2017

The Urban Soundscapes of the World project aims to set the stage for a standard on recording and reproducing urban acoustic environments with soundscape in mind. Immersive audiovisual recordings, which combine high quality spatial (binaural) audio with 360 degree video, are valuable to serve as an ecologically valid baseline for assessing the perceptual influence of noise control and soundscaping measures through auralization. As architects and designers commonly work by example, one of the goals of this project is to compile a comprehensive reference database of well-documented exemplars. These are to be recorded at a range of urban sites with a wide variety of soundscapes, in order to be able to achieve a good statistical power in any subsequent analysis. For this purpose, a protocol for selecting recording locations and time periods in a systematic way is developed, based on a common questionnaire that is conducted among panels of local experts in each selected city. The questionnaire contains open questions to look for public spaces inside the city that are perceived in various ways, regarding the presence of sound sources, the perceived affective quality and the appropriateness of the sound environment.
How does activity affect soundscape assessments? Insights from an urban soundscape intervention with music
Authors: Steele Daniel , Tarlao Cynthia , Bild Edda , Rice Julian , Guastavino Catherine
Published: June 2017

The relationship between activity and soundscape has recently garnered research attention, particularly in public spaces. In the summer of 2015, we installed an interactive sound system (Musikiosk) in a busy public park allowing users to play their own content over high-quality speakers. Questionnaires (N = 197) were administered over 3 conditions: pre-installation with park users, during the installation phase with Musikiosk users, and during the installation phase with park users not using Musikiosk. For users and observers of Musikiosk, a separate evaluation of the Musikiosk intervention was also included. The questionnaire included quantitative evaluations (soundscapes scale from Swedish Soundscape Quality Protocol, restorativeness, mood, noise sensitivity), free response data (soundscape description, self-reported activity, sound source identification, reasons for park visit), and demographic info (age, interaction with others, proximity of residence). The qualitative descriptions of activity and sound sources were categorized into emergent themes. Presented here is the analysis of the interaction between activity and soundscape assessment in terms of quantitative variables and qualitative descriptions.
Introduction and management of noise low emission zones: LIFE MONZA project
Authors: Bellomini Raffaella , Silvaggio Rosalba , Luzzi Sergio , Borchi Francesco
Published: June 2017

The introduction of Low Emission Zones, an urban area subject to road traffic restrictions in order to ensure compliance with the air pollutants limit values, set by the European Directive on ambient air quality (2008/50/EC), are common and well-established actions in the administrative government of the cities and the impacts on air quality improvement are widely analyzed, while the effects and benefits concerning the noise have not been addressed in a comprehensive manner. The definition, the criteria for analysis, and the management methods of a Noise Low Emission Zone are not yet clearly expressed and shared. LIFE MONZA project (Methodologies for Noise low emission Zones introduction and management—LIFE15 ENV/ IT/000586) addresses these issues. The first objective of the project, co-funded by the European Commission, is to introduce an easy-replicable method for the identification and the management of the Noise Low Emission Zones, an urban area subject to traffic restrictions, whose impacts and benefits regarding noise issues will be analyzed and tested in the pilot area of the city of Monza, located in North Italy. Background conditions, structure, and objectives of the project will be discussed in this paper.
Music to some, noise to others; reducing outdoor music festivals' sonic impact on surrounding communities. Case study: KAABOO 2016
Authors: Vassilakis Pantelis , Davis Aaron
Published: June 2017

For music scenes to coexist and thrive alongside residential communities, approaches to the problem of music as noise must acknowledge the impact of noise signal type on listener annoyance levels. The challenge has yet to be properly addressed by the environmental acoustics community, which focuses on measurement standards and mitigation techniques applicable to mechanical noise but unfit to address noise issues related to music. Differences include short versus long range contexts, health versus annoyance considerations, and continuous/unintelligible versus time-variant/intelligible source signals. Noise ordinances often introduce further complications, requiring disambiguation to provide valid/assessable expectations. The presentation outlines how the problem was successfully tackled for KAABOO 2016, a large-scale open-air music festival involving over 100 acts, over 75,000 patrons, and multiple outdoor stages. We discuss (a) working with the city and venue to fine-tune noise ordinance expectations and support valid compliance assessment; (b) designing and deploying sophisticated sound systems, powerful enough to fulfill audience expectations and focused enough to effectively reduce noise impact on the surrounding communities; (c) cooperating with the artists’ teams to appropriately reduce on-site levels; and (d) obtaining relevant noise data prior and during the event to validly capture the event’s noise impact and formally assess compliance.
An examination of the variations in estimated models for predicting annoyance due to supersonic aircraft noise
Authors: Carr Daniel J. , Davies Patricia
Published: June 2017

There is a need for good criteria to evaluate the acoustic outcomes of designs of future commercial supersonic aircraft. Such criteria could be used with sound predictions to assess impact on communities under flight paths of supersonic aircraft. While surveys of communities exposed to supersonic aircraft noise should be part of the criteria development and validation, some candidate models of people’s responses need to be developed to help focus the design of the community tests. While several tests have been conducted, the models proposed to predict annoyance differ. Analysis of response data from several sonic boom subjective tests is presented. Either indoor or outdoor sounds have been used in the tests, and the models are based on metrics from indoor and from outdoor sounds. The effects of the environment in which the people hear the sounds, the signal sets used in the tests and in the analysis, the metrics and types of models used are discussed.
NASA’s Low Boom Flight Demonstration: Assessing community response to supersonic overflight of quiet supersonic aircraft
Authors: Coen Peter , Loubeau Alexandra , Pauer Brett
Published: June 2017

Innovation in Commercial Supersonic Technology is one of six thrusts that guide NASA’s Aeronautics Research. The near term objective of this activity is establishment of standards for acceptable overland supersonic flight, in cooperation with international standards organizations. To accomplish this objective, NASA believes the next step is to conduct a flight demonstration using a research aircraft designed to produce not a sonic boom, but a quieter “thump” sound. Based on the success of recent research, NASA has initiated design studies on a Quiet Supersonic Technology (QueSST) Aircraft. The Flight Demonstration will culminate in a series of campaigns in which the QueSST aircraft will be flown over communities. Surveys will be conducted to develop a database of public response to the sounds. This data will support ongoing international efforts to develop the noise certification standard. While the first flight of the aircraft is still a few years away, NASA recognizes there is much to be done to prepare for the community response test phase. This includes community identification and engagement, survey and instrumentation design and local and Federal government approvals. The paper will present background and of NASA planning to date, and solicit input from the research community on next steps.
Development of a metric utilizing outdoor sonic boom for correlating indoor human annoyance responses
Authors: Morgenstern John M.
Published: June 2017

In 2015, the CAEP (Committee for Aviation Environmental Protection) SSTG (SuperSonic Task Group) assessed over 70 metrics for resolving acceptability of sonic booms. A ground rule was metric application to the outdoor sonic boom signature. Studies indicate people spend 90% of time indoors and sonic boom is expected to be the same or more annoying indoors. NASA developed an IER (Indoor Environment Room) facility to simulate indoor sonic booms and collected 30 humans’ responses to 140 representative booms. Because all other metrics were based on human perception of loudness without indoor effects, a new metric was developed. Previous work suggested indoor annoyance from sonic booms was predominantly based upon indoor loudness, building response and associated rattle. This new metric combines one metric for indoor loudness and one metric for building response and rattle. Indoor loudness [PL(i)] is based upon the highest correlated outdoor metric, PL, but calculated after adjusting 1/3 octave levels for transmission loss. Building response (BR) averages of 1/3 octave levels in the 10-40 Hz range. The combined metric correlated the NASA indoor data with an R2 of 0.939, higher than the next best metrics: ISBAP 0.921, PL(i) 0.910 and PL 0.881.
Effects of model fidelity on indoor sonic boom exposure estimates
Authors: Klos Jacob
Published: June 2017

Commercial supersonic flight is prohibited over land, but this may change in the near future with the introduction of supersonic aircraft that produce a substantially quieter sonic boom. A transient modal interaction model is used to simulate the acoustic and vibration environment inside a large ensemble of residential homes to estimate the range in levels to which residents may be exposed during overflight of low-boom supersonic aircraft. However, the choice of fidelity used in the finite element models of the house structure (e.g., walls, floors, roofs, etc.) may have an impact on these exposure estimates. This presentation documents a recent study in which the fidelity of the structural finite element models was varied. Model fidelity was either an orthotropic panel approximation, in which the stiffening effects of studs were smeared over the entire panel, or a model that explicitly modeled the sheathing and studs. For sonic boom noise, it was found that the orthotropic panel approximation performs well for partitions that have through-the-thickness geometric symmetry, for example walls with two sheathing surfaces. However, the orthotropic approximation does not perform as well for panels with only one sheathing surface, which is typical of floors, ceilings, and roofs.
Sonic boom weather analysis of the F-18 low boom dive maneuver
Authors: Page Juliet
Published: June 2017

In support of community low boom test planning, a sonic boom analysis of ten years of weather data was conducted at multiple coastal regions for an F-18 conducting the NASA low boom dive maneuver. The low boom dive maneuver involves an inverted dive where the aircraft accelerates supersonically and then pulls out above 30,000 Ft. During the dive maneuver, the sonic booms arrive on both egg and crescent shaped isopemps. Due to the supersonic flight conditions and the propagation paths the boom from the earlier parts of the trajectory arrive before the later part of the flight path. The influence of the local meteorological conditions on this maneuver has a striking effect on the sonic boom footprints, including the shape and location of the focal zone and the extent of the low-amplitude sonic boom carpet region. The paper will describe the PCBoom sonic boom propagation results and interpretive techniques for assessing potential coastal sites for conducting dose-response testing using the F-18 dive maneuver.
A numerical study of infrasound scattering from atmospheric inhomogeneities based on the 3-D unsteady compressible Navier-Stokes equations
Authors: Sabatini Roberto , Marsden Olivier , Bailly Christophe , Gainville Olaf
Published: June 2017

A direct numerical simulation of the compressible unsteady Navier-Stokes equations is performed to investigate the 3-D nonlinear acoustic field generated by a high-amplitude infrasonic source placed at ground level in a realistic atmosphere. High-order finite differences and a Runge-Kutta time integration scheme originally developed for aeroacoustic applications are employed. The atmosphere is parametrized as a stationary and vertically stratified medium, constructed by specifying a speed of sound and a mean wind profiles which mimic the main trends observed during the Misty-Picture experiment. In the present talk, after a general description of the acoustic field observed up to 140 km altitude and 450 km range, the scattering from stratospheric inhomogeneities is investigated. The spectrum of the scattered wave recorded at ground level is more particularly discussed and its dependence on the spectral properties of the inhomogeneities is highlighted. A fast method for computing the scattered field, based on a wavelet representation of the temperature and wind fluctuations, is finally presented.
Local infrasound propagation in three dimensions simulated with in situ atmospheric measurements
Authors: Kim Keehoon , Rodgers Arthur , Seastrand Douglas
Published: June 2017

Local infrasound propagation is influenced by atmospheric conditions. The vertical gradients of local ambient temperatures and winds can alter the effective sound speed profiles in the atmosphere and dramatically change the focusing and defocusing behaviors of acoustic waves at local distances. Accurate prediction of local infrasound amplitude is critical to estimating explosion energies of natural and/or man-made explosions, and physics-based numerical simulation that accounts for three-dimensional propagation effects should be required for that purpose. The accuracy of a numerical modeling is, however, often compromised by the uncertainty of atmospheric parameters that are used for the modeling. In this study, we investigate the impacts of local atmospheric conditions on infrasound propagation using the data from chemical explosion experiments. In situ atmospheric conditions during the experiments are measured by a combination of (1) local radiosonde soundings, (2) Atmospheric Sounder Spectrometer for Infrared Spectral Technology (ASSIST), (3) surface weather stations, and (4) a wind LIDAR profiler, which can complement atmospheric profiles for numerical simulations and capture local atmospheric variability. We simulate three-dimensional local infrasound propagation using a finite-difference method with the local atmospheric measurements, and the accuracy of the numerical simulations are evaluated by the comparison with the field observations.
Local-distance acoustic propagation from explosions
Authors: Arrowsmith Stephen , Downey Nathan , Preston Leiph , Bowman Daniel C.
Published: June 2017

We study the effect of acoustic propagation from explosions on full waveforms using both empirical and numerical approaches. Empirically, we explore the effects of meteorology, terrain, etc., on explosion signatures by exploiting a rich dataset of explosion measurements in different regions to relate specific path effects to second-order effects in the waveforms. Numerically, we explore the effects using different full wave codes to understand observations from a unique experiment with both ground and air waveform and 3D wind field measurements. We discuss implications for explosion yield estimation for surface explosions and for underground events.
The study of sudden stratospheric warmings using infrasound
Authors: Smets Pieter , Assink Jelle , Evers Läslo
Published: June 2017

Infrasound has a long history in monitoring SSWs. Several pioneering studies have focused on the various effects of a major warming on the propagation of infrasound, described throughout this chapter. A clear transition can be denoted from observing anomalous signatures towards the use of these signals to study anomalies in upper atmospheric specifications. First studies describe the various infrasonic signatures of a major warming. In general, the significant change in observed infrasound characteristics correspond to summer-like conditions in midwinter. More subtle changes are denoted during a minor warming, recognizable by the presence of a bidirectional stratospheric duct. A combined analysis of all signal characteristic unravels the general stratospheric structure throughout the life cycle of the warming. From then on, infrasound observations are used to evaluate the state of the atmosphere as represented by various NWP models. A new methodology, comparing regional volcano infrasound with simulations using various forecast steps, indicates interesting variations in stratospheric skill.
Estimating the effects of an ellipsoidal earth and topography on infrasonic propagation
Authors: Blom Philip
Published: June 2017

Infrasonic signals often propagate significant horizontal distances so that predictions obtained using a flat ground approximation can introduce inaccuracies. Simulations of propagation in an atmospheric layer around a spherical globe have shown non-negligible deviations from flat ground predictions for both arrival locations and propagation times. Simulation predictions for flat-ground and spherical earth models will be discussed and the additional challenges of implementing a non-spherical globe model and the inclusion of topography will be discussed using the approximation of geometric acoustics. A non-spherical globe model, such as the WGS84 ellipsoid, is found to produce range dependence in the propagation medium, even in the case that a stratified local atmosphere is assumed. Further, although scattering and diffraction effects are not included in the geometric limit, variations in the ground surface level can be included in ray path computation to more accurately model propagation of infrasound. Propagation effects will be detailed in the case of a tropospheric waveguides for which interaction with the ground surface is significant as well as the case that source and receiver locations have differences in elevation.
Spectral broadening of infrasound tones in mountain wave fields
Authors: DAMIENS Florentin , MILLET Christophe , LOTT Francois
Published: June 2017

Linear theory of acoustic propagation is used to analyze how infrasounds trapped within the lower tropospheric waveguide propagate across mountain waves. The atmospheric disturbances produced by the mountains are predicted by a semi-theoretical mountain gravity wave model. For the infrasounds, we solve the wave equation under the effective sound speed approximation both using a spectral collocation method and a WKB approach. It is shown that in realistic configurations, the mountain waves can deeply perturb the low level waveguide, which leads to significant acoustic dispersion. To interpret these results, we follow each acoustic mode separately and show which mode is impacted and how. We show that during statically stable situations, roughly representative of winter or night situations, the mountain waves induce a strong Foehn effect downstream which shrinks significantly the waveguide. This yield a new form of infrasound absorption, a form that can largely outweigh the direct effect of the mask the mountain induce on the low-level waveguide. On the opposite, when the low level flow is less statically stable (summer or day situations), the mountain wave dynamics does not produce dramatic responses downstream, it can even favor the passage of infrasound waves, somehow mitigating the direct effect of the obstacle.
From physiology to functional auditory-nerve models: Challenges and approaches
Authors: Verhulst Sarah
Published: June 2017

A variety of auditory-nerve models, as well as a vast amount of animal single-unit and population response data that can be used to set the parameters of such models, exists. However, it is hard to evaluate different model implementations from published data to decide whether the specific implementation is appropriate for your envisioned application. In this presentation, I will give an experience-based overview on the challenges faced with when evaluating the model parameters in auditory-nerve models. The adopted approach uses the available computer code of the different models under test, and compares their responses to the same input. This method is very efficient in testing the influence of changing one specific part of the model while leaving the rest unchanged, and can ultimately yield improved functional models of the auditory periphery.
Reproducing response characteristics of electrically-stimulated auditory nerve fibers with a phenomenological model
Authors: Takanen Marko , Seeber Bernhard U.
Published: June 2017

Electrical stimulation of the auditory nerve fibers (ANFs) by a cochlear implant (CI) restores hearing for profoundly deaf people. Modern CIs use sequences of amplitude-modulated charge-balanced pulses to encode the spectro-temporal information of the sound reaching the ears of the listener. In such a pulsatile stimulation, several temporal phenomena related to inter-pulse interactions affect the responsiveness of the ANF during the course of the stimulation. Specifically, refractoriness, facilitation, accommodation, and spike-rate adaptation affect whether a given pulse evokes an action potential or not, and these phenomena continue to provide challenges for computational models. Here, we present a model that builds on recent the biphasic leaky integrate-and-fire model by Horne et al. (Front. Comput. Neurosci. 2016), which we have extended to include elements that simulate refractoriness and facilitation/accommodation by affecting the threshold value of the model momentarily after supra- and subthreshold stimulation, respectively. We show that the revised model can reproduce neurophysiological data from single neuron recordings considering the aforementioned phenomena. By accurate modeling of temporal aspects of inter-pulse interactions, the model is shown to account also for effects of pulse rate on the synchrony between the pulsatile input and the spike-train output. [Work supported by BMBF 01 GQ 1004B.]
Predicting binaural lateralization and discrimination using the position-variable model
Authors: Stern Richard M.
Published: June 2017

The position-variable model was developed as a means to characterize and predict a variety of binaural lateralization, discrimination, and detection phenomena. The model was motivated by a desire for a more complete understanding of the putative mechanisms by which interaural time and intensity differences were combined, as well as the extent to which results in interaural discrimination and binaural detection experiments are mediated by cues based on subjective lateral position. This paper will describe recent efforts to unify and extend the predictions of the model, as well as to develop a publicly accessible version of the model within the framework for comparing evaluating binaural models described by Dietz et al. in this session. Predictions of the model are based on computation of the centroid along the internal-delay axis of the patterns of activity of the display of information proposed earlier by Jeffress and Colburn, derived from the auditory-nerve response to the experimental stimuli. Some of the issues to be discussed include comparisons to other proposed methods of developing lateralization predictions, the impact of internal versus external noise in the model’s predictions, and specific issues involved with modifying the model to render it compatible to the common framework for model comparison.
Open community platform for hearing aid algorithm research
Authors: Kayser Hendrik , Herzke Tobias , Loshaj Frasher , Grimm Giso , Hohmann Volker
Published: June 2017

The project “Open community platform for hearing aid algorithm research” funded by the National Institutes of Health (NIH Grant 1R01DC015429-01) aims at sustainable, focused research toward improvement and new types of assistive hearing systems. To this end, an open-source software platform for real-time audio signal processing will be developed and made available to the research community including a standard set of reference algorithms. Furthermore, novel algorithms for dynamic and frequency compression, auditory-scene-analysis based noise suppression and speech enhancement, and feedback management will be investigated. For a realistic assessment of the benefits of hearing aid algorithms and combinations thereof, instrumental measures of performance in virtual acoustic environments of varying complexity will be included in the algorithm design and optimization. With such a quasi-standard set of benchmarks and the means to develop and integrate own signal-processing methods and measures in the same framework, the platform enables reproducible, comparative studies and collaborative research efforts. Beyond an implementation for PC hardware the system will also be made usable for ARM-processor based hardware to allow pre-development of wearable audio devices—so-called “hearables.” This contribution will present underlying previous work and the goals and plans of the project that has started midyear 2016. www.openMHA.org.
Open science in the Two!Ears project—Experiences and best practices
Authors: Wierstorf Hagen , Winter Fiete , Spors Sascha
Published: June 2017

Two!Ears was an EU funded project for binaural auditory modeling with ten international partners involved. One of the project goals was to follow an Open Science approach in all stages. This turned out to be a challenging task as the project involved huge amounts of software, acoustical measurements, and data from listening tests. On the other hand, it was obvious from the positive experience with the Auditory Modelling Toolbox that an Open Science approach would have a positive impact and foster progression afterwards. As there existed no ready solution to achieve this goal at the beginning of the project, different paths for data management were tested. It was especially challenging to provide a solution for data storage. Here, the goal was not only the long term accessibility of the data, but also the revision control of public and private data for the development inside the project. In the end, the project was able to make most of its software and data publicly available, but struggled to apply the reproducible research principle to most of its papers. This contribution will discuss best practices to actively support reproducible research in large-scale projects in the acoustic community, points out problems and solutions.
A library of real-world reverberation and a toolbox for its analysis and measurement
Authors: Traer James , McDermott Josh
Published: June 2017

Reverberation distorts the sounds produced in the world, but in doing so provides information about the environment. This distortion is characterized by the Impulse Response (IR) and depends upon the material and geometry composing the environment. For some tasks (voice recognition, source localization, acoustic tomography, etc.), reverberation must be discounted, but for others (room identification, distance estimation, etc.), it must be analyzed. Our recent work on the perception of reverberation has leveraged measurements of real-world IRs, which exhibit a number of regularities that the brain appears to have internalized for auditory scene analysis. Here, we present a library of these measurements and a toolbox for measuring and analyzing additional IRs. The library contains 271 IRs from spaces encountered by 7 volunteers over 2 weeks of daily life, and thus reflects the distribution of typical reverberation experienced by humans. The toolbox includes procedures for measuring IRs with low-cost, portable equipment, with a low-volume broadcast. This allows measurement in both public and outdoor spaces. Both the library and toolbox are publicly available.
Auditory protection, observation vs standards
Authors: Fleischer Gerald
Published: June 2017

A summary of more than two decades of research, related to the relationship between the acoustic environment and the auditory threshold. Special groups have been examined: professional musicians, dentists, fans and avoiders of discotheques, office personnel, nomadic people, etc. Persons who suffered from noise-induced damage have been examined, and the acoustic conditions, mostly impulses, reenacted and analyzed. Depending on the pressure-time-history, impulses show several types of characteristic damage (footprints). These types of damage can be determined automatically, using pattern recognition, if more frequencies are used for audiometry. Evidence for training of the auditory system is widespread. A cochlear mechanism for reducing the sensitivity very rapidly appears likely and is presented and discussed. Middle-ear muscles are responsible for auditory accommodation—listening to events nearby while suppressing noise from a distance. They are not helpful for avoiding typical damages caused by noise. Using these parameters gives a much better understanding what is harmful for hearing. This is helpful for avoiding such conditions. Comparing the auditory threshold between various groups, independent of age, reveals what is good for hearing.
The open virtual auditory-localization environment: Towards a common methodology for objectively evaluating head-related transfer function personalization methods
Authors: Romigh Griffin D. , ayers jason
Published: June 2017

Despite the fact that individualized head-related transfer functions (HRTFs) are critical for achieving high-fidelity virtual audio representation, the techniques for measuring them, which have been around for decades, are too costly for most potential users. As such, many strategies have been proposed that aim to improve virtual audio fidelity by personalizing a non-individualized HRTF based on input (or anthropometric information) from the user. Unfortunately, evaluations of these methodologies have varied widely from purely computational to purely subjective, making comparisons across studies or to objective behavioral performance metrics difficult. The current work presents the Open Virtual Auditory-Localization Environment (OpenVALE), a software toolkit for providing a common, objective, HRTF-based auditory localization task via new, relatively low-cost, commercial VR headsets. The heart of OpenVALE is a server application that allows researchers to dynamically load custom HRTFs, present spatialized auditory stimuli, collect hand- or head-slaved, cursor-based localization responses, and provide visual feedback, all through simple string-based IP socket messages from any compatible client application (e.g., Matlab, Java, Python, etc.). An initial validation of the task environment, based on individualized HRTF measurements, will be described along with a discussion of the remaining challenges for creating an accepted standard methodology.
Attenuation of dual hearing protection: Measurements and finite-element modeling
Authors: Nélisse Hugues , Sgard Franck C. , Gaudreau Marc-André , Padois Thomas
Published: June 2017

In extremely noisy environments, it is normally recommended to use a combination of earplug and earmuff, denoted here as a dual protection, to protect workers from the excessive noise. Unfortunately, it has been shown repeatedly that the attenuation values obtained with the dual protection are generally less than the sum of the individual earplug and earmuff attenuation values. In the literature, this is generally explained by the bone conduction path and the coupling between the earplug and the earmuff. However, there is much less work devoted to examining in detail the coupling between the earplug and the earmuff. In this work, experimental results on human subjects and on an artificial text fixture are collected using REAT and MIRE procedures for different combinations of earmuffs and earplugs. Additionally, a finite-element model is used to investigate the physics of the problem and to better understand the nature of the coupling between the earplug and the earmuff when used in a dual configuration. Results from the experimental procedures as well as from the FE model are presented and discussed. These results clearly illustrate the importance of the coupling between the earplug and the earmuff when used in combination.
Correlation of flow field and acoustic output from hearing aids under influence of wind
Authors: Zenger Florian , Gerstner Linda , Lodermeyer Alexander , Becker Stefan
Published: June 2017

Wind noise in hearing aids occurs even at low wind speeds and is a confounding factor for hearing aid wearer, hence leading to a reduction of speech intelligibility. In this submission, a study on the correlation of the flow field around a hearing aid to its acoustic output is made. The BTE (behind the ear) hearing aid is mounted on an artificial head with three different ear geometries. The flow field is captured using a two component PIV (particle image velocimetry) system. For exposing critical flow phenomena, a POD (proper orthogonal decomposition) of the PIV measurement data is made. The hearing aid output is measured with a microphone inside the artificial head. On the one hand, wind noise in hearing aids is generated by the fluctuating velocity field of the boundary layer on the hearing aid. On the other hand, based on the PIV data and the POD results, flow patterns around the artificial head and the hearing aid are detected, which cause further noise, that is captured by the hearing aid microphones. With these findings, modifications on the hearing aid geometry are deduced, that lead to a decrease in wind noise and hence to a better speech intelligibility.