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Show Abstract BOOK REVIEWS UNDERWATER SOUND [30] Comparison of in-air evoked potential and underwater behavioral hearing Field airborne sound isolation in multifamily construction evaluation of metrics within ASTM E Global active control of broadband noise from small axial cooling fans, Part 2.
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The results are obtained in two characteristic urban configurations - canyon and non- canyon streets. The paper addresses the problem of the computational complexity of the algorithms which results in long execution times and inhibits measurements on a larger scale. Various methods for algorithm optimization are explored by varying different parameters such as angular resolution, signal length, various algorithm specific parameters, etc.

The sensitivity of output results on the variation of these parameters is analyzed. The goal is to create a time efficient measurement procedure which would enable the acquisition of a larger data set covering various urban terrain configurations. When monitoring critical structures, fatigue fracture, deformations, holes and much more are cases of failure which must be detected at an early stage.

Changes in the modal parameters eigenfrequencies, damping ratios, and mode shapes of the structure allow conclusions to be drawn about the extent and location of the deterioration, subject to appropriate preliminary examination. Conventional measurement methods i. In contrast, the use of a suitable microphone array allows the high-resolution acquisition of the entire surface vibration covered by the array. Thus, the modal parameters of interest are determined by measuring the pressure fluctuations in the near field of the structure.

A commercial acoustic camera with microphones Fibonacci by gfai tech GmbH is used for this purpose. On the basis of artificially generated failure cases load fracture, inhomogeneities, etc. As a reference, simulated vibration analyses, as well as vibration analyses measured by laser vibrometers, are used. The sound field in a room is often modeled as a superposition of elementary waves, such as plane or spherical waves. These wave expansions provide a powerful means to interpolate or extrapolate the sound field within and outside the measurement domain.

However, projecting the sound field of a large domain in a room into a planar or spherical wave base yields a high number of very elementary components. We examine the use of dictionary learning to find a set of more complex basis functions that are suitable to represent the sound field enclosed in a room.

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The resulting dictionary should be able to capture the dominant features of the sound field, and represent it using only a sparse set of functions. In this study, extensive measurements of the sound pressure in a room are obtained and used as a training set to learn a dictionary. We analyze the spatial properties of the learned dictionary, and compare it to simple elementary basis functions such as plane and spherical waves. Demand for calibration at infrasonic frequencies has emerged in response to earth monitoring problems. The primary standard for sound pressure is defined through the reciprocity calibration method specified in the International Electrotechnical Commission IEC Standard This method is based on the use of closed couplers and is routinely applied by the National Metrology Institutes for a large frequency range; however, infrasonic frequencies below 2 Hz have not been explored until recently.

The acoustic transfer admittance of the coupler, including the heat conduction effects of the fluid, must be modelled precisely to obtain accurate microphone sensitivity. IEC provides two standardised solutions for the correction of heat conduction. However, researchers have noted significant deviations between these corrections at low frequencies in plane wave couplers, indicating that one or both techniques incorrectly calculate the influence of heat conduction. In this paper, the limitations of the standardised formulations at infrasonic frequencies are identified and two alternative solutions are proposed.

An experiment is also reported, which highlights the discussed limitations of the standardised formulations for acoustic transfer admittance, while also demonstrating the validity of the proposed alternative formulations at frequencies down to 0.

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The multi-channel Wiener Filter MWF is a well-known speech enhancement technique that can be used to improve speech quality and intelligibility of microphone signals recorded in noisy and reverberant environments. It is commonly assumed that i late reverberation and ambient noise can be modeled as a spatially diffuse sound field and ii the spatial coherence of the remaining noise is known a-priori. Using these assumptions, the MWF requires estimates of the relative early transfer functions RETFs of the target speaker and the power spectral densities PSDs of the target speaker, the diffuse and the remaining noise.

Recently, we proposed a technique to jointly estimate these quantities by minimizing a model-based error matrix via an alternating least squares ALS method. In this contribution, we present extensive simulation results comparing the ALS method with a state-of-the-art reference method based on covariance whitening.


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We demonstrate the effectiveness of the ALS method in both stationary and dynamic acoustic scenarios by using the estimates in an MWF and evaluating its noise reduction and dereverberation performance with respect to the improvement in speech quality. Results show that the ALS method yields more accurate estimates than the reference method, especially in the presence of strong uncorrelated noise.


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Hearing thresholds are usually reported in decibel units, which gives conveniently compressed numbers with biological implications. However, the decibel scale causes confusion when in-air thresholds are compared to underwater ones. Not only are the reference pressures of the in-air and underwater scales different, but the interpretation of the thresholds also depends on whether we assume the ear is detecting the integrated sound intensity or squared pressure that is, if the acoustic impedance difference between the two media should be compensated for. Here, in-air and underwater hearing thresholds from the literature on toothed whales, seals, marine birds and turtles are compared, both using decibel scales and linear pressure and sound intensity units.

The interpretation of how sensitive an animal is to sound in air and underwater critically depends on the choice of units used to report hearing thresholds. Therefore, great care must be taken choosing the adequate units in hearing studies.

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Modern cetaceans have their origins in terrestrial mammals that started their aquatic life over 50 million years ago. The history of the earliest whales, the archaeocetes, is fairly well known, and in their skull anatomy one can follow their adaptation to life and hearing underwater, while the earliest ones of them were still able to live and hear on land, too. Mysticetes and odontocetes both stem from archaeocetes, but today these two groups live in very different acoustic worlds, having specialized in low and high frequencies, respectively.

It is also apparent that they use different kinds of peripheral auditory mechanisms. It is currently under lively debate whether the ability to hear high frequencies was present already in late archaeocetes, with mysticetes then later specializing in low frequencies, or if the ability to hear high frequencies first appeared with the odontocetes.

Sounds emitted by modern whales can be compared to their hearing characteristics, when these are available. Morphological data on the peripheral auditory structures can be used to predict hearing ranges of these animals. These questions will be reviewed and discussed in this presentation.

All groups of tetrapods have members that adopt aquatic lifestyles with adaptations also of their auditory system. Water is a high pressure, low particle motion medium, and the consequence is that an efficient underwater ear is sensitive to sound pressure.

It is often stated that underwater hearing can work efficiently without a middle ear apparatus by bone conduction, but the sensitivity of such an ear is limited by the very low particle motion in water. A comparison of tetrapods ranging from totally aquatic the clawed frog Xenopus laevis and mostly aquatic the red-eared slider Trachemys scripta to mostly terrestrial the cormorant Phalacrocorax carbo sinensis show similar features.

All have tympanic middle ears with an air-filled middle ear cavity. The eardrum vibration peaks at the resonance frequency of the middle ear cavity air volume and the eardrum is modified plate-like. Sensitivity to sound pressure is slightly lower in water than in air, making underwater hearing much more efficient in terms of sound energy.

Consequently, the slightly modified tympanic ears of these species are efficient aquatic sound receivers. During the buzz phase of small odontocetes, such as porpoises, inter click intervals ICI may be as low as 2ms, which would seem to preclude individual processing of clicks. We studied the low-frequency auditory evoked potentials AEP in a stationary porpoise presented with artificial clicks at ICIs of 0. There is a persistent component in the AEPs occurring at latencies out to at least ms, and it seems highly likely that this represents remnants of cortical processes, whereby ms should form a lower limit to the ICIs at which click-by-click processing of echoes could take place.

Toothed whales do therefore not process echo information before emission of the next click. As an added bonus, we believe that the relatively slow components of the AEPs constituting the cortical contributions hold potential for assessing the audiogram of odontocetes electrophysiologically down to frequencies well below what is usually thought possible with traditional amplitude modulated tonal stimuli, often taken to be limited to frequencies above several kHz.

Diving birds may spend several minutes underwater during foraging dives. However, surprisingly little is known about avian underwater hearing.

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We do not know their sensitivity or even if they respond to underwater sound. To help filling this gap we measured the audiograms of cormorants Phalacrocorax carbo sinensis and studied their ear anatomy. Wild-caught fledglings were anesthetized and their auditory brainstem response ABR to clicks and tone bursts was measured, first in an anechoic box in air and then in a large water-filled tank with their head and neck submerged 10 cm below the surface.

The overall shape of their air-audiograms was like that reported for birds of the same size in air. The bandwidth and slopes of their audiograms were similar in air and water. However, in air the highest sensitivity was found at 2 kHz, whereas it was displaced towards lower frequencies underwater.

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These results suggest that cormorants have rather poor in-air hearing compared to similar-sized birds. Their underwater hearing sensitivity, however, is higher than what would have been expected for purely air-adapted ears. A possible reason for the poor in-air sensitivity is the special ear anatomy with the central eardrum shaped as a rigid piston like in turtles. Internally coupled ears ICE , where an interaural cavity acoustically couples the eardrums, are an anatomical trait present in more than half of all terrestrial vertebrates.

The superposition of outside and internal pressure on the two eardrums results in internal instead of interaural time and level differences, which are keys to sound localization. Although ICE is primarily a low-frequency terrestrial adaptation, the African clawed frog Xenopus laevis is a fully aquatic species with a distinct air-filled canal between the ears. In water, the speed of sound is four times that in air. Unlike terrestrial animals with ICE, the Xenopus interaural cavity is also medially connected to the lungs. By modeling the inflated lungs as a Helmholtz resonator, we demonstrate their effect in improving hearing in a low-frequency regime, while simultaneously enhancing sound localization in a disjoint high-frequency regime, corresponding to the frequency ranges of male advertisement calls.

In conjunction with its unique plate-like eardrums, we show how Xenopus uses its ICE-like interaural coupling to generate considerable internal level differences between eardrum vibrations and thus overcomes the challenges of underwater sound-localization. Taken together, the two arguments of Helmholtz resonator and plate-like eardrums show the potency of ICE and are interpreted accordingly.

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