bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential contribution of target and masker temporal fine structure to the segregation of speech from noise.
Authors: Apoux Frederic C. , Berg Carla Y. , Yoho Sarah E. , Healy Eric W.
Published: July 2011

In recent years, it has been suggested that the normal auditory system relies on temporal fine structure (TFS) cues to segregate speech from noise. Based on previous work, we hypothesized that only the target TFS is critical for understanding speech in noise. To assess this hypothesis, the TFS of the target and that of the masker were manipulated simultaneously or independently. Four masker types were used. A 30-band vocoder was used to replace the original TFS of the stimuli with tones. Results showed a significant drop in performance when the TFS of the target and that of the masker were disrupted simultaneously. They also showed a significant drop in performance when only the TFS of the target was disrupted. In contrast, disruption of the masker TFS had no effect on intelligibility. Overall, the present data are consistent with previous work showing that TFS information plays a significant role in speech recognition in noise, especially when the noise fluctuates over time. However, the present study indicates that listeners rely primarily on TFS information in the target and that the nature of the masker TFS has a very limited influence on the outcome of the unmasking process. [Work supported by NIDCD.]
Concurrent profile analysis: The effect of segregation cues on spectral-shape comparisons for simultaneous stimuli.
Authors: Shen Yi , Richards Virginia M.
Published: July 2011

The ability to accurately perceive spectral information from one sound source in the presence of others is crucial for speech understanding in complex and challenging environments. In the present study, non-speech stimuli, a pair of concurrent complex tones, were used to obtain psychophysical measurements of this ability in a controlled setting. Listeners detected whether the spectral profiles of the two concurrent complexes were the same or exchanged across two observation intervals. Concurrent profile analysis thresholds were measured as the minimum amount of spectral alterations for the detection of the change. Thresholds were measured from four normal hearing listeners and as functions of three types of segregation cues: difference in fundamental frequency, difference in interaural time differences, and onset asynchrony. The roles of these cues in concurrent spectral-shape analysis are discussed in terms of the underlying psychometric functions.
Relationship between selective auditory attention and brainstem encoding in musicians and non-musicians.
Authors: Zhu Li , Xia Jing , Shinn-Cunningham Barbara
Published: July 2011

This study explores whether differences in performance in a challenging selective auditory attention task are related to the strength of the sub-cortical encoding of stimulus pitch. In each behavioral trial, two simultaneous digits, differing in pitch by 6 semitones, were presented. A preceding visual cue instructed listeners to report the target digit with either the higher or lower pitch. Subjects both were more accurate at reporting the target digit and had a shorter reaction time when the visual-cue-to-auditory-target interval was long compared to trials with a short preparatory interval. Moreover, behavioral performance was generally better for subjects with musical training than for non-musicians. The brainstem frequency-following responses (FFRs) were recorded in response to a complex tone in both quiet and in noise for the same listeners. Consistent with past reports, musicians demonstrated a stronger FFR than non-musicians; in addition, the musicians’ FFR response was less affected by noise compared to non-musicians. The strength of the FFR correlated with individual performance on the pitch-based selective auditory attention task. Results suggest that the robustness of the brainstem encoding of acoustic inputs directly determines the ability to selectively attend to an auditory target using pitch differences.
On the spatial resolution of using the Helmholtz equation least squares method to visualize coherent point sources in a free field.
Authors: Dziklinski Richard , Wu Sean
Published: July 2011

Reconstruction of the sound fields by coherent sources has always been a great challenge for the acoustics community because any slight phase shifts among coherent sound waves can cause significant changes in the results. This paper explores the feasibility of using the Helmholtz equation least squares (HELS) and modified HELS based nearfield acoustical holography (NAH) to visualize coherent point sources in a free field. Our goal here is to locate the coherent sources precisely, but not to reconstruct their amplitudes accurately. In particular, we examine the spatial resolution limitations in using HELS and modified HELS to locate coherent sources, and why the guidelines established for the Fourier acoustics based NAH and Shannon–Nyquist sampling rate can by violated. Moreover, the impacts of stand-off distance, frequency, microphone spacing, source separation distance, and signal to noise ratio on the spatial resolution offered by HELS and modified HELS are studied through numerical simulations. The results are compared with those obtained by the Fourier acoustics. Test results show that the modified HELS always provides the highest spatial resolution over the widest range of application scenarios, and to achieve comparable spatial resolution, Fourier acoustics requires much more measurement points than HELS and modified HELS methods do.
Experimental validations of using the Helmholtz equation least squares method to visualize coherent sources.
Authors: Dziklinski Richard , Wu Sean
Published: July 2011

This paper presents experimental validations of using the Helmholtz equation least squares (HELS) method to locate coherent sources. Tests were conducted inside a fully anechoic chamber. Two speakers were used to produce coherent sound waves and their phases controlled by the “waveplay” function in MATLAB©. The speakers were covered by two cones heavily insulated to minimize sound transmission through openings and side walls. A nylon tube (0.5 m long, 9 mm OD, and 3 mm ID) was used to facilitate plane wave propagation from the apex of the cone to the end of the tube to mimic sound radiation from a point source. The acoustic pressures were measured by a 5 x 5 microphone array with 12.5-mm spacing among individual microphones. Source separation, stand-off distance, and frequency were selected based on limitations of the methods determined from numerical simulations. Results show good correlation with numerical simulations, validating that HELS and modified HELS can be used to locate coherent point sources in violation of spatial resolution guidelines established for Fourier acoustic based NAH and Shannon–Nyquist sampling rates. Similar reconstruction resolution with Fourier acoustics based NAH requires significantly more measurement points and may not visualize the sources as well as HELS does.
Multi-reference methods for nearfield acoustical holography.
Authors: Kim Yong-joe , Lee Moohyung , Bolton J. Stuart
Published: July 2011

Holographic projection requires that sound fields be spatially coherent. That condition can be satisfied if data at all locations on the hologram surface are measured simultaneously. However, more commonly, a scanning procedure is used in which measurements are made on parts of the hologram surface in sequence. In the latter case, it is necessary to record signals from fixed-location reference transducers so that the phase of the pressure in each scan segment can be determined. Further, if the sound field is radiated by statistically incoherent sub-sources, the sound field must be decomposed into coherent partial fields before holographic projection is performed on the individual partial fields. For the partial field decomposition to be successful, the number of reference transducers must be greater than or equal to the number of incoherent sources generating the field. In this presentation, the state-of-the-art of multi-reference procedures applied to nearfield acoustical holography will be described. Requirements for the number and positioning of reference transducers will be given along with procedures to verify that the number of references chosen is sufficient. Further, post-processing of measured data to position virtual reference transducers close to physically meaningful sources and to compensate for source non-stationarity will be discussed.
Statistically optimal nearfield acoustical holography in subsonically moving fluid medium.
Authors: Kim Yong-Joe , Niu Yaying
Published: July 2011

Statistically optimal nearfield acoustical holography (SONAH) can be used to reconstruct 3-D sound fields by projecting 2-D sound pressure data measured on a small measurement aperture. When the sound pressure data are measured by using a small microphone array mounted on a high-speed vehicle, the mean flow effects of a moving fluid medium should be considered in the SONAH procedure. Here, an improved SONAH procedure is thus proposed that includes the mean flow effects. The backward projection performance of the proposed SONAH procedure is also improved by using a wave number filter to effectively reduce subsonic noise components that are exponentially amplified during the backward projection. For the purpose of validating the proposed SONAH procedure, a monopole simulation at a fluid medium velocity of Mach = −0.6 is conducted. The sound fields reconstructed by using the proposed SONAH procedure lead to more accurate sound source locations and radiation patterns than the conventional NAH and SONAH procedures. An experiment with two loudspeakers is performed in a wind tunnel operating at Mach = −0.12. The locations and radiation patterns of the two loudspeakers can be successfully identified from the sound fields reconstructed by using the proposed SONAH procedure.
Cylindrical Fourier near-field acoustical holography applied to a high-power jet.
Authors: Krueger David W. , Gee Kent L. , Wall Alan T. , Sommerfeldt Scott D. , Blotter Jonathan D.
Published: July 2011

Near-field acoustical holography as a method to reconstruct sound fields near military jet aircraft is being investigated. Measurements were recently made on the F-22 Raptor using a linear, ground-based array of microphones at a distance of 11 m from the centerline. Analytic continuation is used to extend the measurement aperture, and, assuming axisymmetry, cylindrical Fourier near-field acoustical holography is used to reconstruct the sound field. Because of the highly directional nature of the source and the effects of wrap-around error from the Fourier transform, the desired reconstruction distance (10–20 m) and the number of points to analytically continue the measurement are directly proportional. Furthermore, given the measurement standoff distance, inverse propagation to the source requires near-complete regularization of the evanescent wave components. [Work supported by Air Force SBIR.]
Cortical rhythms to native and non-native phonetic contrasts in infants and adults.
Authors: Bosseler Alexis N. , Taulu Samu , Imada Toshiaki , Pihko Elina , Ahonen Antti , Mkelä Jyrki P. , Kuhl Patricia K.
Published: July 2011

Infants change from universal language-general listeners to language-specific listeners in the first year of life. Studies show that statistical learning affects this change. As learning ensues, the power of statistical information subsides and a reliance on learned categories emerges. We posited that phonetic processing is anchored by two strategies that shift during development: statistical learning during the initial stage before phonetic categories are acquired, and learned categories during adulthood when categories are fully formed. We examined whether the strategy transition could be indexed using cortical brain rhythms (theta) that reflect cognitive effort. Using magnetoencephalography (MEG) we examined theta in response to native and nonnative speech sounds at 6–8 months, 10–12 months, and adulthood. Several advances in MEG analysis were required to test infants. Supporting our hypothesis, the results revealed that theta power increases for frequent stimuli, regardless of language, at 6–8 months. In adults, theta increases were shown for non-native categories regardless of frequency. 12-month-old infants are in transition and show intermediate values. The results indicate that cortical brain rhythms will be valuable in relating speech development to higher cognitive processes.
Investigating the spatiotemporal neural dynamics of lexico-semantic activity in 12–18 month old infants by combining magnetoencephalography and magnetic resonance imaging.
Authors: Travis Katherine E. , Leonard Matthew K. , Brown Timothy T. , Hagler Donald , Dale Anders M. , Elman Jeff L. , Halgren Eric
Published: July 2011

Knowledge of the neural basis of early language is limited because of the difficulties in assessing functional brain activity during infancy. Consequently, it is unclear whether infants and adults depend on similar underlying neural structures to understand words. Advances in magnetoencephalography combined with magnetic resonance imaging now make it possible to study this population. This method, dynamic statistical parametric mapping (dSPM), has been extensively validated during language processing in adults. Here, dSPM was used to examine the neural correlates of word understanding in 12–18 month old infants. Specifically, it was discovered that the lexico-semantic neural processes indexed as the adult N400 event-related component are functional during early stages of word learning and depend on similar left frontotemporal brain areas. These findings demonstrate that dSPM can be used to localize functional brain activity associated with language processes in pediatric populations. Moreover, discovery of a fundamental lexico-semantic process present throughout the rapid burst of language acquisition permits this process to be quantified and thus related to behavioral and neural development and their disorders. Together, these findings illustrate the potential for dSPM and other non-invasive neuroimaging techniques to increase current understandings of the neural basis of early language development. [Work supported by the Kavli Institute for Brain and Mind and NIH/NINDA R01 NS018741.]
Time dependency of cortical specialization and integration in speech perception.
Authors: Zhang Yang
Published: July 2011

Speech perception research has been greatly enriched by technical advancement in neuroimaging. Here electroencephalography (EEG) and magnetoencephalography (MEG) data from infant and adult subjects are reported to demonstrate the feasibility and importance of distributed source estimation and time-frequency analysis in understanding the time-dependent nature of cortical specialization and integration in speech processing. Advantages and limitations of the current analysis approaches for EEG and MEG data are discussed in relation to functional magnetic resonance imaging. The results collectively call for a dynamic time-dependent approach toward proper characterization of the functional neuroanatomy and hemispheric lateralization of spoken language.
The roles of relative distance and gaze in neural processing of spatial demonstratives.
Authors: Stevens James , Zhang Yang
Published: July 2011

This study collected both behavioral and event-related potential (ERP) data to investigate neural processing of two spatial demonstrative expressions in English, this and that, in social communication. The experimental design employed congruent and incongruent conditions for audiovisual scenarios involving the speaker, the hearer, and the referred-to object. Behavioral data showed that distance determined the demonstrative form only when the hearer shared the speaker’s gaze at the object. ERP data indicated signficant congruent versus incongruent differences in the poststimulus window of 525–725 ms for the expected demonstrative form, that, when an object was near the hearer and when the interlocutors shared gaze. Global field power (GFP) analysis showed the effect at an earlier window (200–500 ms). There were also significant GFP effects at 100–200 and 300–775 ms associated with specific spatial configurations in relation to the near-far perceptual distance and shared gaze. Furthermore, standardized low resolution brain electromagnetic tomography (sLORETA) revealed significant activation associated with processing the semantic incongruency effect at the left temporal cortex and the parietal lobe bilaterally. The results demonstrate that the neural mechanisms of spatial deixis processing are sensitive to contextual integration of distance and gaze in social interaction.
Why do blind listeners use visual cortex for understanding ultra-fast speech?
Authors: Dietrich Susanne , Hertrich Ingo , Ackermann Hermann
Published: July 2011

Individuals with vision impairment of a peripheral, e.g., retinal origin, may learn to understand spoken language at a rate of up to 22 syllables (syl) per second, exceeding by far the maximum performance level of sighted listeners (ca. 8 syl/s). To delineate the brain network subserving this skill, 14 blind individuals (different proficiency in understanding ultra-fast speech) and a sighted control group underwent functional magnetic resonance imaging. In addition to perisylvian cortex and left-hemisphere supplementary motor area (SMA), significant hemodynamic activation of right-hemisphere primary visual cortex (V1), left-hemisphere fusiform gyrus (FG), and bilateral pulvinar emerged during ultra-fast speech perception (16 syl/s) in trained blind people. Dynamic causal modeling analysis revealed skill-dependent intrinsic connections from Heschl’s gyrus (right > left) and pulvinar to V1, from V1 to perisylvian areas and SMA as well as from FG to Broca’s area. Conceivably, cooperation of right-hemisphere Heschl’s gyrus, V1, and left SMA enhances the temporal sequencing of syllable structure of ultra-fast utterances which, in turn, accelerates the segmentation of speech sounds at the level of perisylvian cortex and left-hemisphere FG. The pulvinar—an audiovisual relais station–might support the synchronization of V1 activity with central-auditory processing. [Work supported by the German Research Foundation (DFG; SFB 550/B1) and the Hertie Institute for Clinical Brain Research, Tuebingen.]
Magnetic brain activity directly reflects syllable onsets and pitch periodicity of a perceived speech signal.
Authors: Hertrich Ingo , Dietrich Susanne , Ackermann Hermann
Published: July 2011

Continuous speech evokes electrophysiological brain activity following the speech envelope (ENV), resembling the N100 responses to single acoustic events. Using magnetoencephalography (MEG), the present study tested further aspects of evoked activity, considering the positive part of the first derivative of the speech envelope (SYL), emphasizing syllable onsets, and a sinosoidal signal representing pitch periodicity (PIT), obtained by 50–180 Hz bandpass filtering of the rectified speech signal. MEG signals, recorded while the participants (n = 10) listened to 4-s portions of natural or formant-synthesized speech at a moderately fast or ultrafast speaking rate, were cross-correlated with ENV, SYL, or PIT. Using dipole models, the cross-correlated MEG signals were evaluated with respect to latency and amplitude of typical components. As expected, the ENV derivate showed an M100-like response that was stronger over the right as compared to the left hemisphere. Regarding the SYL derivate, a more anterior component could be isolated, in addition to M50/M100-like responses in the auditory system, presumably representing a late frontal component of the M50 deflection. The PIT derivate showed multiple peaks of alternating polarity bound to a central-auditory source. The strength of these MEG components depended on rate and signal type.
Variations of inverted seabed sound speed from different receivers on a horizontal cross-range line array.
Authors: Wan Lin , Zhou Ji-Xun , Rogers Peter H.
Published: July 2011

In the Shallow Water 2006 experiment conducted on the New Jersey continental shelf, a set of broadband combustive sound source (CSS) signals was measured by a horizontal cross-range line array with 36 receivers. The 230-m-long array was exactly perpendicular to the direction of sound propagation. The modal dispersion characteristics are used to estimate the seabed sound speed by matching the theoretical and measured modal arrival time differences. The measured modal arrival time differences along such a short array vary from one receiver to another at 10–20 km away from the source. This causes variations in the inverted seabed sound speed. This paper analyzes both the variations of inverted seabed sound speed and the horizontal cross-range correlation coefficient as a function of receiver separation. [This work was supported by the Office of Naval Research.]
Measurements and interpretation of mesoscale seabed spatial variability.
Authors: Holland Charles W. , Nielsen Peter L. , Dettmer Jan , Dosso Stan E.
Published: July 2011

Acoustic propagation, reverberation, and clutter may be controlled by sediment spatial variability in some environments. Many of the geoacoustic measurement approaches currently employed in the ocean acoustics community provide measurements of sediment properties at either fine scales, less than O(101) m (e.g., probes and cores) or at large scales spatially averaged over lateral scales greater than O(10III) m. Relatively little is understood about the mesoscale, defined here as scales from O(10I–103) m. Recent wide-angle reflection measurements resolve lateral spatial variability down to a few meters over track lengths of order 10 km and provide early observations of sediment lateral variability at the mesoscale. [Work sponsored by the Office of Naval Research Ocean Acoustics Program and the NATO Undersea Research Centre.]
Bayesian inversion of seabed reverberation and scattering data.
Authors: Dosso Stan E. , Holland Charles W.
Published: July 2011

This paper describes a Bayesian approach to the inversion of ocean acoustic reverberation data for scattering and geoacoustic parameters of the seabed. The seabed is modeled as a sediment layer over a semi-infinite basement. Interface scattering occurs at the (rough) upper and lower boundaries of the sediment layer, and volume scattering occurs within the layer (the scattering mechanisms are considered to be independent and are modeled using perturbation theory and the Born approximation). Unknown parameters include geoacoustic properties (sediment-layer thickness and sound speeds, densities, and attenuations for sediments and basement) and scattering properties (roughnesses and scattering strengths for upper and lower sediment boundaries, and volume scattering strength). One dimensional (1-D) and two-dimensional (2-D) marginal probability distributions are computed from the multidimensional posterior probability density (PPD) using Metropolis–Hastings sampling applied in a principal-component parameter space to provide efficient sampling of correlated parameters. Results indicate that reverberation inversion is a strongly nonlinear inverse problem, with highly multimodal marginal distributions and strong interparameter correlations. Addressing this nonlinearity is of key importance to understanding the information content of reverberation data. [Work funded by the ONR.]
Trans-dimensional geoacoustic inversion.
Authors: Dettmer Jan , Dosso Stan E. , Holland Charles W.
Published: July 2011

This paper applies a general trans-dimensional Bayesian methodology to geoacoustic inversion. Trans-dimensional inverse problems are a generalization of fixed-dimensional inversion that include the number and type of model parameters as unknowns in the problem. By extending the inversion state space to multiple sub-spaces of different dimensionality, the posterior probability density quantifies the state of knowledge regarding inversion parameters, including effects due to limited knowledge about appropriate parametrization of the environment and error processes. The algorithm applies a reversible-jump Markov chain and the seabed is parametrized as a partition model. The unknown data errors are addressed by including data-error standard deviations as unknowns. Dimensional jumps are implemented with a birth-death methodology that allows transitions between dimensions by adding or removing sediment interfaces to/from the partition model while maintaining unbiased sampling. Trans-dimensional inversion results in an inherently parsimonious solution while partition modeling provides a naturally self-regularizing algorithm based on data information content. Together, this results in environmental estimates that quantify appropriate seabed structure as supported by the data, allowing sharp discontinuities while approximating smooth transitions where needed. This approach applies generally to geoacoustic inversion and is illustrated here for seabed reflection coefficient data collected on the Malta Plateau. [Work supported by ONR.]
Internal waves’ role in determining probability distribution of coherent integration time near 133 Hertz and 3709 kilometers in North Pacific Ocean.
Authors: Spiesberger John
Published: July 2011

The hypothesis tested is that internal gravity waves limit the coherent integration time of sound at 3709 km in the Pacific Ocean at 133 Hz and a pulse resolution of 0.06 s. Five days of continuous transmissions at 2 min intervals are examined. The source and receiver are mounted on the bottom of the ocean with timing governed by atomic clocks. Measured variability is only due to fluctuations in the ocean. A model for the propagation of sound through fluctuating internal waves is run without any tuning with data. Excellent resemblance is found between the model and data’s probability distributions of integration time up to a day, which is the largest lag explored. The probability that the integration exceeds a day or more is about 0.15. The model under-predicts the probability of occurrence of integration times less than 10 min. However, the overwhelming agreement at longer times supports the conclusion that the standard spectrum of internal waves accurately explains almost all of the distribution of measured integration time. The ocean supports very long coherent integration times because its fluctuations cause the acoustic phasors to fluctuate following non-canceling probability distributions. [Work supported by the Office of Naval Research Contracts N00014-06-C-0031 and N00014-10-C-0480.]
Spectra of acoustic travel time at periods shorter than 33 h at basin-scales in the North Pacific Ocean: Horizontal diffusion of upper turning points.
Authors: Spiesberger John
Published: July 2011

Previously unexplained fluctuations of acoustic travel time (133 Hz, 0.06 s resolution, 3709 km transmission) at periods between 3.3 and 10 h are likely due to a standard spectrum of internal gravity waves even though the travel times of features arriving 3 to 4 s apart change travel times by nearly the same amount at the same time. This paradox is resolved by appreciating that nearly all acoustic arrivals consist of tens to hundreds of temporally-unresolved arrivals whose upper turning points diffuse horizontally between the normal 50-km periodicity of paths. Similar behavior is obtained from numerical calculations with fluctuations based only on internal waves. The horizontal diffusion of acoustic turning points appears to also explain the presence of non-stationary oscillations at periods up to 33 h. A simple algebraic calculation shows that these longer oscillation periods with amplitudes of about 5 ms are probably due to inertial currents generated by surface winds. If these oscillations are due to inertial currents, these data might be used to study their spatial and temporal scales both in and below the mixed layer. This might be useful for understanding dissipation mechanisms. [Work supported by ONR contract N00014-10-C-0480.]
Potential causes of increasing low-frequency ocean noise levels.
Authors: Ainslie Michael A.
Published: July 2011

A simple expression for the global average ambient noise is derived in terms of parameters representing the characteristics of the sound sources, the number of such sources and the propagation properties of the deep ocean, and used to explore possible causes of increasing low frequency noise in the deep ocean. A 5 dB increase in noise level over 35 years, reported by Andrew et al. [ARLO 3, 65–70 (2002)], is explained by the increase in the total number of ocean-going ships and their average tonnage, with no evidence of any significant change in source level during that time. The theoretical effect of increasing transparency to low-frequency sound, which has been proposed as a possible cause of part of this increasing noise [Hester et al., Geophys. Res. Lett. 35, L19601 (2008)], is less than 1 dB to date, increasing in the 21st century by an amount that depends on the accompanying change in temperature.
On the use of noise budgets to assess the effects of offshore wind farms on marine life.
Authors: Miller James H. , Potty Gopu R. , Casagrande David S. , Vigness Raposa Kathleen J. , Miller Lisa A. , Nystuen Jeffrey A. , Scheifele Peter M. , Clark John Greer
Published: July 2011

An ocean noise budget is a list of sources of noise along with their average intensity in a particular frequency band [Frisk et al. (2003)]. The budget can be calculated from acoustic data collected by the passive aquatic listener (PAL) systems [Nystuen and Howe (2005); Miller et al. (2008)]. In the far field, the average acoustic intensity of plane waves can be computed in 1/3-octave bands over some duration. The assumption is made that the noise in the band at any one time is dominated by a single, identifiable source such as wind, rain, shipping, fish, marine mammals, etc. The duration and instantaneous intensity of the acoustic signal is used to calculate the average. Identification is carried out using the ratios of various spectral levels as outlined in the work of Ma et al. [(2005)]. We apply the concept of noise budgets to the assessment of the impact of long term noise from offshore wind turbines on marine life. A developer has proposed to construct more than 200 wind turbines south of Rhode Island. A noise budget has been calculated for the region from data collected on PALs. The addition of the 200 turbines will be incorporated into the budget parametrized on source level.
The under-ice soundscape in Great Slave Lake near the City of Yellowknife, Northwest Territories, Canada.
Authors: Martin Bruce S. , Cott Pete A.
Published: July 2011

The Department of Fisheries and Oceans and JASCO deployed an AMARs sound data recorder in Great Slave Lake near Yellowknife, Northwest Territories, between December 2009 and March 2010. One of the objectives of these recordings was to provide long-term ambient noise measurements in a large frozen lake near a major urban center. A recent study reported spot-measurements of under-ice noise in a subarctic lake from anthropogenic activity raising the sound levels up to 46 dB above ambient, and 10-h average ambient levels that were very low (spectral density levels of ∼45 dB re 1 μPa). The current Great Slave Lake data provide the opportunity to determine the long-term baseline of under-ice sound levels and how anthropogenic activity, such as air and ice-road traffic, adjacent to the study site affects the ambient levels and how these sounds may impact aquatic biota. Regressions of the ambient levels against wind speed and temperature are also discussed.
Long-term ambient noise measurements in the Hudson River.
Authors: Martin Bruce S. , Vallarta Jonathan
Published: July 2011

Long-term recordings of ambient noise levels in the Hudson River near the Tappan Zee bridge were made between August and November 2010. Twelve recorders were deployed for 2 days in August, and six recorders were deployed for the complete 3 month program. Concurrent logging of meteorological and tidal data was performed, as well as measurements of bridge traffic and rail traffic along the east side of the river. The overall sound levels in the river are comparable to sea-state zero. Analysis of the data has shown that bridge traffic strongly influences the sound levels only within a few hundred feet of the bridge. Tidal and river flow are dominant noise sources near the river’s deep channel. Anthropogenic sources, especially pleasure craft, are transient noise sources throughout the river.
A review of mixing time estimators.
Authors: Defrance Guillaume
Published: July 2011

In 1967, Joyce introduced the concept of dynamical systems in the room acoustics community. Based on statistical physics from the early 20th century, Joyce assumed large halls to be ergodic and mixing. Since that time, the hypothesis of mixing rooms has been accepted, but only a few studies have focused on the experimental validation of such an assumption. In 1982, Polack proposed a heuristic formulation of the mixing time, based on perceptual criteria. After that time, the sound field is, theoretically, uniform throughout the room, i.e., the density of sound rays must be homogeneous and isotropic at any time in the phase space. Many acousticians have related the mixing time to the beginning of the diffuse sound field, also called the late reverberation. In a recent work, we have investigated two different approaches for experimentally estimating the mixing time from measured impulse responses. We present these two estimators and explain our results. In particular, we show that the relationship between mixing and late reverberation is not straightforward. Finally, we conclude that mixing may occur later after the beginning of late reverberation. Consequently, instead of mixing time, we propose the term of cross-over time.
Understanding the perceptual effects of diffuser application in rooms.
Authors: Robinson Philip W. , Braasch Jonas , Xiang Ning
Published: July 2011

Acoustic diffusers have been applied in rooms for echo elimination and reduction of spatial variation, but perceptual effects are not fully understood. At worst, diffusive surfaces have been blamed for tonal distortion and coloration, while other studies have found high correlation between preferred concert halls and diffusive interior surfaces. Evaluating perceptual effects of diffusive surfaces presents several unique challenges. While many geometric acoustic modeling programs incorporate spatial scattering algorithms which produce perceivable differences in auralization results and may accurately reproduce acoustic parameters of real halls, these differences are not necessarily representative of the perceptual effects of diffuser application in rooms. Accurate investigations of diffusion can be conducted using real or scale model room measurements, but equalization must be performed to isolate the independent effects of scattering and absorption. This paper presents experimental methods to objectively gauge the perceptual effect of scattering surfaces.
Numerical prediction of sound diffusion from surfaces with fractal geometry.
Authors: Snow Erik , Bradley David T.
Published: July 2011

Sound diffusive and scattering surfaces can be implemented in architectural spaces to improve the acoustical qualities of the space, particularly by attenuating the effects of harsh reflections and by producing a more diffuse sound field. These surfaces typically are effective only for a limited range of frequencies, dependent on the scale of the surface geometry. Given the broad frequency range of human hearing, an ideal diffuser would provide scattering across many frequencies. There is a direct relationship between surface roughness size and the wavelength of the scattered sound; therefore, scale-invariant fractal surfaces can be useful in achieving this ideal. In this study, virtual two-dimensional (2-D) fractal surfaces have been generated using the random midpoint displacement (RMD) algorithm, with fractal characteristics in both one and two dimensions. The sound diffusive properties of these surfaces were numerically predicted using the boundary element method (BEM). Several input parameters of the fractal generation algorithm have been varied, such as the number of iterations to which the algorithm is carried out, and the average difference of the random displacements from a mean flat surface. The effects of these parameters on the diffusion coefficient of the surfaces have been predicted. Results and analysis will be presented.
Effects of surface scattering and room shape on the correspondance between statistical- and geometrical-acoustics model predictions and real sound fields.
Authors: Summers Jason E.
Published: July 2011

Much of room acoustics relies on approximate models of sound. The high-frequency approximation of geometrical acoustics, in which sound is modeled by ensembles of classical phonons, is the basis for many computational modeling techniques. The earliest mathematical model of sound in rooms, given by Sabine’s decay equation, is a statistical approximation that assumes homogenous and isotropic (diffuse) sound fields and continuous absorption processes. Sabine’s statistical-acoustics model is related to geometrical acoustics as a limiting case for rooms that are ergodic, sufficiently mixing, and weakly absorbing. Various semi-empirical corrections are possible (e.g., Eyring and Kuttruff), though a true first-order correction requires additional information. Surface scattering (as characterized by scattering and diffusion coefficients) and room shape are critical in determining the relationship between statistical- and geometrical-acoustics predictions, as these physical attributes determine key statistical properties of phonon trajectories: path-length distributions, statistical independence of reflections, and the sequence with which possible paths are explored. Along with a theoretical overview of the role of scattering and room shape, this presentation describes several computational investigations into these relationships together with a corresponding series of scale-model experiments in which the results were validated. [Prior work supported by the Bass Foundation and RPG Diffusor Systems, Inc.]
A rule based approach to the Design of Auditoria.
Authors: Oldham David
Published: July 2011

The past 100 years has witnessed a considerable amount of research aimed at improving our understanding of the way in which sound behaves in auditoria. However, there remains a need for transferring much of this knowledge into the design process. Ideally, the designer should be able to access this knowledge at all stages of design and thus to ensure the achievement of good acoustical conditions in the finished project. In this paper, a rule based approached to room acoustic design, implemented on a personal computer, is described. All rules are related to relevant research findings and presented in such a way as to leave the designer with sufficient leeway to enable him or her to explore a range of innovative solutions.
New approaches for studying the perception of vocal signals in otariid pinnipeds.
Authors: Mulsow Jason , Finneran James J.
Published: July 2011

The pioneering work of Ronald Schusterman and David Kastak considered the acoustic signaling of pinnipeds from the perspectives of both sender and receiver. Their work often highlighted the otariid pinnipeds (sea lions and fur seals), which are known for their frequent, loud aerial vocalizations. Numerous aerial vocalizations have been described for otariids, and research has demonstrated that a number of call characteristics are sufficient for individual and species recognition. In contrast to the marked interspecific variability found in these vocalizations, laboratory studies with pure-tone stimuli suggest that the aerial hearing capabilities of otariids are nearly identical among species. This is a surprising result, as many components in the calls of otariids exist at frequencies well below the range of best hearing sensitivity. Future studies can potentially examine the relevance of frequency composition and other vocalization parameters using psychophysical methods that include complex acoustic stimuli and an analysis of subject response latencies. Such methods have proven useful for studying the manner in which birds perceptually categorize vocalizations [Dooling et al., J. Comp. Psychol. 101, 367–381 (1987)] and they may provide novel tools for investigating the link between vocalization structure and auditory perception in otariids. [Work supported by ONR.]
Vocal recognition of individuals versus relative dominance rank among breeding male northern elephant seals (Mirounga angustirostris).
Authors: Insley Stephen J. , Holt Marla M. , Southall Brandon L.
Published: July 2011

Whether an animal truly recognizes an individual or a simple rule-based category (e.g., neighbor or offspring) has important behavioral and evolutionary implications such as the accuracy of social reciprocity. Many tests of individual recognition have focused on neighboring territorial males (“dear enemy” or “neighbor-stranger” recognition). Unfortunately the static territorial context of these tests, mostly with male songbirds, opens them to the criticism of being merely associative habituation. More dynamic mating assemblages, such as leks where vocally advertising animals encounter numerous others, are a potentially rich and largely untested alternative. The female defense polygyny practiced by male northern elephant seals during terrestrial breeding is such a dynamic system. To examine whether elephant seals were recognizing individuals or dominance categories we conducted a total of 53 playback experiments to 18 males at Año Nuevo State Reserve. Each playback was a series of threat calls assigned to four dominance conditions relative to the subject. Dominance was based on the outcomes of interactions among contesting male dyads. Responses were measured using three assays in situ and from video records of each experiment. Results thus far are consistent with the males not recognizing individuals but instead recognizing and responding appropriately to relative rank.
Directionality of male northern elephant seal (Mirounga angustirostris) threat calls and how it influences receiver behavior.
Authors: Holt Marla M. , Southall Brandon L. , Insley Stephen J. , Schusterman Ronald J.
Published: July 2011

Many animal sounds are directional in which the sound energy is focused in a direction that depends on the signaler’s orientation. In the 1970s, Ron Schusterman quantitatively showed this in barking California sea lions and dogs. Several investigators have suggested ways that such features might be particularly useful among individuals in acoustic communication networks. However, only a few have tested such hypotheses experimentally and even fewer have investigated how directional signals affect receiver behavior. In this study, we measured directivity patterns of male northern elephant seal threat calls and used an acoustic playback approach to determine how call directionality influenced the responses of male seals in reproductive competition. We collected data on adult and older subadult seals on a breeding rookery (Ano Nuevo State Park) over three field seasons. Threat calls had substantial directionality, particularly at frequencies above 1 kHz and responses to playbacks depended on call directivity patterns. Males moved farther away from the playback source when it simulated a caller oriented toward them compared to when playbacks simulated a caller oriented away from them. These results suggest that threat call directionality provides meaningful information about the auditory scene and spatial orientation of male elephant seals in reproductive competition.
Developmental change in ultrasonic echolocation sounds of Japanese echolocating bats, Pipistrellus abramus.
Authors: Hiryu Shizuko , Riquimaroux Hiroshi
Published: July 2011

The development of vocalization during the first post-natal month in Pipistrellus abramus was studied. Vocalizations were recorded from each pup (five pups from two mothers; captive-born and captive-raised in a laboratory) everyday when isolated from its mother. The sounds produced by pups on the day of birth were categorized into a long isolation call and seemingly an echolocation precursor call (EP call). The terminal frequencies of the fundamental (TF) was 19.3 ± 1.9 kHz (n = 98), indicating that TF ranges of the second harmonic produced by newborn bats almost corresponded to the fundamental TF of adult pipistrelle (40∼45 kHz). The bats over 2 weeks of age mainly produced EP calls whose characteristics were changed with age. (1) increased TF, (2) decreased pulse duration, (3) increased bandwidth, and (4) constant inter-pulse interval. The TF at 4 weeks old showed no significant difference from TF of adult pipistrelle (41.6 ± 2.0 kHz, P = 0.8). We recorded echolocation pulses of pups (31 days old) during their first flight in a flight chamber. The results show that (1) practice flights appeared to be unnecessary to modify IPI or duration with a distance and (2) the bats emitted paired pulses (strobe groups) in 2 days after the first flight. [Work supported by JSPS and ONR.]
Computational model of a bioinspired broadband receiver for sonar clutter reduction.
Authors: Gaudette Jason E. , Knowles Jeffrey M. , Barchi Jonathan R. , Simmons James A.
Published: July 2011

Echolocating bats have the ability to seamlessly navigate through dense foliage and other obstacles at flight velocity using only the information available in acoustic returns. The spatial resolution required to perform this feature cannot be explained by conventional beamforming and pulse design techniques. We describe a biologically inspired broadband sonar receiver that mimics parallel neural processing by echolocating bats to suppress clutter in complex acoustic environments. These results are incorporated into an improved version of the spectrogram correlation and transformation (SCAT) receiver by replacing the original spectrogram transformation block with a process that translates both harmonic coherence and spectral interference patterns into estimates of echo-delay separations for closely spaced echo highlights. The model treats simple target echoes as highlight reconstructions, and broader lowpass filtered echoes—characteristic of most off-axis clutter—as numerous overlapping poorly defined shapes. The monaural SCAT model for range-only resolution is also expanded to a binaural, 2-D model for high-resolution sonar imaging in the range-azimuth plane. Receiver performance is compared with conventional array processing methods through acoustic simulation and sonar image reconstruction amidst dense clutter. [Work supported by the ONR and internal investments by the NUWC, Division Newport.]
Geoacoustical oceanography: Integrating geology with ocean acoustics.
Authors: Chapman N. Ross
Published: July 2011

Knowledge of the structure and material properties of the ocean bottom is essential for modeling sound propagation in shallow and deep water environments. Significant progress has been made in the past decade in developing inversion methods for estimating geoacoustic profiles that are used to account for the interaction of sound with the ocean bottom in numerical calculations of the sound field in the water. These methods rely heavily on ground truth information about the material properties and structure of the sediment to define realistic prior estimates of the bottom. Ground truth is obtained by various different geological and geophysical techniques such as sediment grab samples and cores, and chirp sonar and high resolution seismic surveys. This paper uses examples from the Shallow Water ‘06 experiment to illustrate the interplay between geological and geophysical information and acoustic data in generating geoacoustic profiles that are effective for modeling sound propagation in shallow water. One example demonstrates the use of prior information in Bayesian matched field inversion, and another example shows the combined use of chirp sonar survey data and modal wavenumber estimation to generate a geoacoustic map of the region.