Neural activity associated with distinguishing concurrent auditory objects

The neural processes underlying concurrent sound segregation were examined by using event-related brain potentials. Participants were presented with complex sounds comprised of multiple harmonics, one of which could be mistuned so that it was no longer an integer multiple of the fundamental. In separate blocks of trials, short-, middle-, and long-duration sounds were presented and participants indicated whether they heard one sound (i.e., buzz) or two sounds (i.e., buzz plus another sound with a pure-tone quality). The auditory stimuli were also presented while participants watched a silent movie in order to evaluate the extent to which the mistuned harmonic could be automatically detected. The perception of the mistuned harmonic as a separate sound was associated with a biphasic negative-positive potential that peaked at about 150 and 350 ms after sound onset, respectively. Long duration sounds also elicited a sustained potential that was greater in amplitude when the mistuned harmonic was perceptually segregated from the complex sound. The early negative wave, referred to as the object-related negativity (ORN), was present during both active and passive listening, whereas the positive wave and the mistuning-related changes in sustained potentials were present only when participants attended to the stimuli. These results are consistent with a two-stage model of auditory scene analysis in which the acoustic wave is automatically decomposed into perceptual groups that can be identified by higher executive functions. The ORN and the positive waves were little affected by sound duration, indicating that concurrent sound segregation depends on transient neural responses elicited by the discrepancy between the mistuned harmonic and the harmonic frequency expected based on the fundamental frequency of the incoming stimulus.     

Formant-frequency matching between sounds with different bandwidths and on different fundamental frequencies

The two experiments described here use a formant-matching task to investigate what abstract representations of sound are available to listeners. The first experiment examines how veridically and reliably listeners can adjust the formant frequency of a single-formant sound to match the timbre of a target single-formant sound that has a different bandwidth and either the same or a different fundamental frequency (F0). Comparison with previous results [Dissard and Darwin, J. Acoust. Soc. Am. 106, 960-969 (2000)] shows that (i) for sounds on the same F0, introducing a difference in bandwidth increases the variability of matches regardless of whether the harmonics close to the formant are resolved or unresolved; (ii) for sounds on different F0's, introducing a difference in bandwidth only increases variability for sounds that have unresolved harmonics close to the formant. The second experiment shows that match variability for sounds differing in F0, but with the same bandwidth and with resolved harmonics near the formant peak, is not influenced by the harmonic spacing or by the alignment of harmonics with the formant peak. Overall, these results indicate that match variability increases when the match cannot be made on the basis of the excitation pattern, but match variability does not appear to depend on whether ideal matching performance requires simply interpolation of a spectral envelope or also the extraction of the envelope's peak frequency.     

一维非线性声波传播特性

针对一维非线性声波的传播问题进行了有限元仿真和实验研究. 首先推导了一维非线性声波方程的有限元形式, 含有高阶矩阵的非线性项导致声波具有波形畸变、谐波滋生、基频信号能量向高次谐波传递等非线性特性. 编制有限元程序对一维非线性声波进行了计算并对仿真得到的畸变非线性声波信号进行处理, 分析其传播性质和物理意义. 为验证有限元计算结果, 开展了水中的非线性声波传播的实验研究, 得到了不同输入信号幅度激励下和不同传播距离的畸变非线性声波信号. 然后对基波和二次谐波的传播性质进行详细讨论, 分析了二次谐波幅度与传播距离和输入信号幅度的变化关系及其意义, 拟合出二次谐波幅度随传播距离变化的方程并阐述了拟合方程的物理意义. 结果表明, 数值仿真信号及其频谱均与实验结果有较好的一致性, 证实计算方法和结果的正确性, 并提出了具有一定物理意义的二次谐波随传播距离变化的简单数学关系. 最后还对固体中的非线性声波传播性质进行了初步探讨. 本研究工作可为流体介质中的非线性声传播问题提供理论和实验依据.     

Measurements of harmonic profiles of a bounded ultrasonic beam in a liquid medium

The acoustic field of a bounded finite-amplitude beam is governed by competing mechanisms such as medium non-linearity, interference, and attenuation. An analytic determination of the distribution of sonic energy in the individual harmonic components is often not reliable; consequently an experimental mapping of those harmonic components may be more appropriate. An experimental method is presented here which involves a miniature hydrophone probe which has been frequency calibrated for each harmonic component using a light diffraction technique. Measurements (made across the sound field) of the acoustic amplitude of the first three harmonic components are presented.     

Measurement of formant frequencies and bandwidths in singing

That singers under certain circumstances adjust the articulation of the vocal tract (formant tuning) to enhance acoustic output is both apparent from measurements and understood in theory. The precise effect of a formant on an approaching (retreating) harmonic as the latter varies in frequency during actual singing, however, is difficult to isolate. In this study variations in amplitude of radiated sound components as well as supraglottal and subglottal (esophageal) pressures accompanying the vibrato-related sweep of voice harmonics were used as a basis for estimating the effective center frequencies and bandwidths of the first and second formants.     

Characteristics of gunshot sound displays by North Atlantic right whales in the Bay of Fundy

North Atlantic right whales (Eubalaena glacialis) produce a loud, broadband signal referred to as the gunshot sound. These distinctive sounds may be suitable for passive acoustic monitoring and detection of right whales; however, little is known about the prevalence of these sounds in important right whale habitats, such as the Bay of Fundy. This study investigates the timing and distribution of gunshot sound production on the summer feeding grounds using an array of five marine acoustic recording units deployed in the Bay of Fundy, Canada in mid-summer 2004 and 2005. Gunshot sounds were common, detected on 37 of 38 recording days. Stereotyped gunshot bouts averaged 1.5 h, with some bouts exceeding 7 h in duration with up to seven individuals producing gunshots at any one time. Bouts were more commonly detected in the late afternoon and evening than during the morning hours. Locations of gunshots in bouts indicated that whales producing the sounds were either stationary or showed directional travel, suggesting gunshots have different communication functions depending on behavioral context. These results indicate that gunshots are a common right whale sound produced during the summer months and are an important component in the acoustic communication system of this endangered species.     

Structural topology optimization on sound radiation at resonance frequencies in thermal environments

Thermal and acoustic environments pose severe challenges to the structural design of hypersonic vehicles.One of them is to find optimal design that exhibits ideal acoustic characteristics in a frequency band,which is discussed in this paper through topology optimization aiming at resonance sound radiation in thermal environments.The sound radiation at resonance frequencies is the main component of response,minimization on which is likely to provide a satisfactory design.A bi-material plate subjected to uniform temperature rise and excited by harmonic loading is studied here.Thermal stress is first evaluated and considered as prestress in the following dynamic analysis;radiated sound power is then calculated through Rayleigh integral.Sensitivity analysis is carried out through adjoint method considering the complicated relationship between stress-induced geometric stiffness and design variables.As the resonance frequency is constantly changing during the optimization,its sensitivity should be considered.It is also noticed that mode switching may occur,so mode tracking technique is employed in this work.Some numerical examples are finally discussed.     

Empirical refinements applicable to the recording of fish sounds in small tanks

Many underwater bioacoustical recording experiments (e.g., fish sound production during courtship or agonistic encounters) are usually conducted in a controlled laboratory environment of small-sized tanks. The effects of reverberation, resonance, and tank size on the characteristics of sound recorded inside small tanks have never been fully addressed, although these factors are known to influence the recordings. In this work, 5-cycle tone bursts of 1-kHz sound were used as a test signal to investigate the sound recorded in a 170-l rectangular glass tank at various depths and distances from a transducer. The dominant frequency, sound-pressure level, and power spectrum recorded in small tanks were significantly distorted compared to the original tone bursts. Due to resonance, the dominant frequency varied with water depth, and power spectrum level of the projected frequency decreased exponentially with increased distance between the hydrophone and the sound source; however, the resonant component was nearly uniform throughout the tank. Based on the empirical findings and theoretical calculation, a working protocol is presented that minimizes distortion in fish sound recordings in small tanks. To validate this approach, sounds produced by the croaking gourami (Trichopsis vittata) during staged agonistic encounters were recorded according to the proposed protocol in an 1800-l circular tank and in a 37-l rectangular tank to compare differences in acoustic characteristics associated with tank size and recording position. The findings underscore pitfalls associated with recording fish sounds in small tanks. Herein, an empirical solution to correct these distortions is provided.     

Mapping the sound field of an erupting submarine volcano using an acoustic glider

An underwater glider with an acoustic data logger flew toward a recently discovered erupting submarine volcano in the northern Lau basin. With the volcano providing a wide-band sound source, recordings from the two-day survey produced a two-dimensional sound level map spanning 1 km (depth) × 40 km(distance). The observed sound field shows depth- and range-dependence, with the first-order spatial pattern being consistent with the predictions of a range-dependent propagation model. The results allow constraining the acoustic source level of the volcanic activity and suggest that the glider provides an effective platform for monitoring natural and anthropogenic ocean sounds.     

Courtship and agonistic sounds by the cichlid fish Pseudotropheus zebra

Courtship and agonistic interactions in an African cichlid species present a richer diversity of acoustic stimuli than previously reported. Male cichlids, including those from the genus Pseudotropheus (P.), produce low frequency short pulsed sounds during courtship. Sounds emitted by P. zebra males in the early stages of courtship (during quiver) were found to be significantly longer and with a higher number of pulses than sounds produced in later stages. During agonistic intrasexual quiver displays, males produced significantly longer sounds with more pulses than females. Also, male sounds had a shorter duration and pulse period in courtship than in male-male interactions. Taken together, these results show that the acoustic repertoire of this species is larger than what was previously known and emphasize the importance of further research exploiting the role of acoustic stimuli in intra- and interspecific communication in African cichlids.     

弹性拍翼悬停时的流固耦合效应

自然界中的昆虫和鸟类大都采用拍翼飞行的策略，其优越的气动表现使拍动飞行方式备受关注.值得注意的是，拍动飞行昆虫和鸟类在实现高机动性的同时，产生的噪音并不十分显著.因此，对拍翼飞行的流固声耦合问题进行研究，揭示其飞行动力学和声学特性，对于应用这类飞行技术具有重要的指导意义.文章采用一种浸入边界法对拍翼悬停时的流固声耦合问题进行数值模拟研究.具体针对刚性拍翼和不同刚度、质量比的柔性拍翼进行了数值模拟，分析了拍翼刚度和质量比对拍翼悬停时的升力和声学特性的影响.结果表明拍翼的转动能有效增加升力，提高效率并降低拍翼运动产生的声音；同时悬停拍翼的近场声受涡的影响明显，尤其是在较大的转动角度时；引入适当的弹性可有效提高拍翼在悬停时的气动表现，包括提高升力系数和效率；综合考虑气动和声学表现，可以看出当无量纲拍动频率在0.3~0.4时，低质量的拍翼（拍翼-流体质量比为1.0）产生的声音较小，同时又具备较高的效率.      

Vibro-acoustic radiation of rigid bodies oscillating at large amplitude and low Mach number: Modelling and experiments

The acoustic radiation of vibrating bodies can usually be considered as a linear phenomenon as in most cases the vibration amplitudes of oscillating bodies are small compared to their dimension. However, in case of large amplitude and small Mach number, the large displacement amplitude of a vibrating body gives rise to geometric nonlinear acoustic effects. In this paper it is shown that the nonlinearity causes an asymmetry in the time signal of the radiated pressure as observed at a fixed position, resulting in harmonic distortion of the radiated sound field. These nonlinear effects can be analysed by the finite element method, using a linear fluid behaviour in combination with a moving mesh approach. This approach is implemented and used to predict the nonlinear sound radiation of lithographic stages oscillating at large amplitude and low Mach number. Acoustic experiments prove the validity of the analysis technique for the geometrical nonlinear phenomena. In addition the structural response of a nearby body excited by the nonlinear acoustic radiation of the stage is calculated and verified experimentally.     

Doppler-shift compensation in the Taiwanese leaf-nosed bat (Hipposideros terasensis) recorded with a telemetry microphone system during flight

Biosonar behavior was examined in Taiwanese leaf-nosed bats (Hipposideros terasensis; CF-FM bats) during flight. Echolocation sounds were recorded using a telemetry microphone mounted on the bat's head. Flight speed and three-dimensional trajectory of the bat were reconstructed from images taken with a dual high-speed video camera system. Bats were observed to change the intensity and emission rate of pulses depending on the distance from the landing site. Frequencies of the dominant second harmonic constant frequency component (CF2) of calls estimated from the bats' flight speed agreed strongly with observed values. Taiwanese leaf-nosed bats changed CF2 frequencies depending on flight speed, which caused the CF2 frequencies of the Doppler-shifted echoes to remain constant. Pulse frequencies were also estimated using echoes returning directly ahead of the bat and from its sides for two different flight conditions: landing and U-turn. Bats in flight may periodically alter their attended angles from the front to the side when emitting echolocation pulses.     

An ecological acoustic recorder (EAR) for long-term monitoring of biological and anthropogenic sounds on coral reefs and other marine habitats

Keeping track of long-term biological trends in many marine habitats is a challenging task that is exacerbated when the habitats in question are in remote locations. Monitoring the ambient sound field may be a useful way of assessing biological activity because many behavioral processes are accompanied by sound production. This article reports the preliminary results of an effort to develop and use an Ecological Acoustic Recorder (EAR) to monitor biological activity on coral reefs and in surrounding waters for periods of 1 year or longer. The EAR is a microprocessor-based autonomous recorder that periodically samples the ambient sound field and also automatically detects sounds that meet specific criteria. The system was used to record the sound field of coral reefs and other marine habitats on Oahu, HI. Snapping shrimp produced the dominant acoustic energy on the reefs examined and exhibited clear diel acoustic trends. Other biological sounds recorded included those produced by fish and cetaceans, which also exhibited distinct temporal variability. Motor vessel activity could also be monitored effectively with the EAR. The results indicate that acoustic monitoring may be an effective means of tracking biological and anthropogenic activity at locations where continuous monitoring by traditional survey methods is impractical.     

Extracting spectral envelopes: formant frequency matching between sounds on different and modulated fundamental frequencies

The four experiments reported here measure listeners' accuracy and consistency in adjusting a formant frequency of one- or two-formant complex sounds to match the timbre of a target sound. By presenting the target and the adjustable sound on different fundamental frequencies, listeners are prevented from performing the task by comparing the absolute or relative levels of resolved spectral components. Experiment 1 uses two-formant vowellike sounds. When the two sounds have the same F0, the variability of matches (within-subject standard deviation) for either the first or the second formant is around 1%-3%, which is comparable to existing data on formant frequency discrimination thresholds. With a difference in F0, variability increases to around 8% for first-formant matches, but to only about 4% for second-formant matches. Experiment 2 uses sounds with a single formant at 1100 or 1200 Hz with both sounds on either low or high fundamental frequencies. The increase in variability produced by a difference in F0 is greater for high F0's (where the harmonics close to the formant peak are resolved) than it is for low F0's (where they are unresolved). Listeners also showed systematic errors in their mean matches to sounds with different high F0's. The direction of the systematic errors was towards the most intense harmonic. Experiments 3 and 4 showed that introduction of a vibratolike frequency modulation (FM) on F0 reduces the variability of matches, but does not reduce the systematic error. The experiments demonstrate, for the specific frequencies and FM used, that there is a perceptual cost to interpolating a spectral envelope across resolved harmonics.     

材料非线性衰减系数的二次谐波测量方法研究

采用有限幅值法测量材料在基波和非线性引起的二次谐波作用下的衰减系数:利用准线性下的KZK方程推导基波和二次谐波的声压分布,并提取波束修正系数;采用短纯音信号进行非线性实验,对检测得到的基波和二次谐波声压进行衍射修正处理,有效抑制衍射对衰减系数测量的不利影响,继而通过线性拟合的方法计算得到更精确的基波和二次谐波的衰减系数。以水为例进行实验,研究了实验测量所得衰减系数的频率依赖关系,结果表明在非线性条件下水的衰减系数与频率间存在较强的线性关系,而线性条件下衰减系数随频率呈现二次方增长的特性则不适用于非线性条件。该研究提出了准确测量非线性声波衰减系数的方法,为更有效地应用非线性超声检测提供理论依据。      

马铁菊头蝠声道声学特性的数值分析

采用有限元数值计算得到了马铁菊头蝠声道内部的声场分布,给出了马铁菊头蝠声道内几种特殊的腔体结构在蝙蝠发声过程中的作用。通过微型CT扫描并经过三维重构得到了马铁菊头蝠声道的三维立体模型用于有限元数值计算,通过在声门处放置单位声源计算得到了整个声道内部以及鼻孔周围的声压分布。结果表明,马铁菊头蝠声道包含了鼻腔结构后声波在声门上方的声压幅度明显大于不含鼻腔结构的情况,从传输曲线来看,声门上方鼻腔的存在使得系统对声波传输在二次谐波频率处呈现低阻抗效果,同时鼻腔的改变还可影响二次谐波的位置。而声门下方的气管空腔主要影响声波的背向转播,声门下方的气管空腔的存在可明显降低蝙蝠发声时声场在声道声门下方的声压幅度,同时抑制声音背向传播时二次谐波成分的强度。      

Perception of acoustic scale and size in musical instrument sounds

There is size information in natural sounds. For example, as humans grow in height, their vocal tracts increase in length, producing a predictable decrease in the formant frequencies of speech sounds. Recent studies have shown that listeners can make fine discriminations about which of two speakers has the longer vocal tract, supporting the view that the auditory system discriminates changes on the acoustic-scale dimension. Listeners can also recognize vowels scaled well beyond the range of vocal tracts normally experienced, indicating that perception is robust to changes in acoustic scale. This paper reports two perceptual experiments designed to extend research on acoustic scale and size perception to the domain of musical sounds: The first study shows that listeners can discriminate the scale of musical instrument sounds reliably, although not quite as well as for voices. The second experiment shows that listeners can recognize the family of an instrument sound which has been modified in pitch and scale beyond the range of normal experience. We conclude that processing of acoustic scale in music perception is very similar to processing of acoustic scale in speech perception.     

The effect of anisotropy of a rough sea surface on the generation of acoustic radiation

A model that relates the frequency-angular characteristics of wind waves on the sea surface to the frequency spectrum of acoustic radiation generated by them is constructed. Based on empirical wave energy distribution functions, it is shown that, in the vicinity of the peak of the wind wave spectrum, the intensity of acoustic radiation strongly depends on the model chosen for the angular distribution function ?(α) and on its parameters. At high frequencies, four to five times higher than the dominant wave frequency, it is possible to assume that, to a first approximation, ?(α) = const. In the intermediate frequency range, between the dominant frequency and the high frequencies, the predominant contribution to the sound radiation is made by the waves that travel in the direction close to orthogonal with respect to the wind.     

Vocal production mechanisms in the budgerigar (Melopsittacus undulatus): the presence and implications of amplitude modulation.

In this paper acoustic evidence is presented for the presence of amplitude modulation in budgerigar (Melopsittacus undulatus) contact calls and learned English vocalizations. Previously, acoustic analyses of budgerigar vocalizations have consisted solely of visual inspection of spectrograms or power spectra (derived from Fourier transformation). Such analyses have led researchers to conclude that budgerigar vocalizations are primarily frequency-modulated, harmonic vocalizations. Although budgerigar calls have been shown to contain regions that are modulated in amplitude, the implications of this fact have been largely ignored. Amplitude modulation, the nonlinear interaction between two separate signals that results in the creation of new, heterodyne (sum and difference) frequencies, can produce a very complex Fourier spectrum that may resemble that produced by a harmonic vocalization. In this paper, the acoustic principles necessary for identifying amplitude modulation present in signals are outlined, and followed by data demonstrating that amplitude modulation is a prominent feature not only of natural budgerigar contact calls, but also of their learned English vocalizations. It is illustrated how analyzing a vocalization that contains amplitude modulation as if it were harmonic can result in misinterpretations of the acoustic and physical properties of the sound and sound source. The implications of amplitude modulation for studies of the ontogenetic, physical, and neural basis of budgerigar vocalizations are discussed, and a potential model for how the budgerigar syrinx may function to produce amplitude modulation is proposed.