bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of late arriving energy on spatial impression
Authors: Bradley John S. , Soulodre Gilbert A.
Published: October 2005

New subjective experiments using sound fields simulated in an anechoic room confirm that spatial impression in concert halls is composed of at least two distinct aspects: apparent source width and listener envelopment. Previously published research has shown that apparent source width is related to the relative level of early lateral reflections. This new work demonstrates that listener envelopment is related to the level, direction of arrival, and temporal distribution of late arriving reflections. It is further shown that increased amounts of listener envelopment decrease the subject’s sensitivity to changes in the apparent source width of the sound field. Listener envelopment is related to objective acoustical measures, and the implications for concert hall design are discussed.
Wave-number domain separation of the incident and scattered sound field in Cartesian and cylindrical coordinates
Authors: Cheng Ming-Te , Mann J. Adin , Pate Anna
Published: October 2005

Two-surface Cartesian coordinate system and cylindrical coordinate system measurement techniques are applied to obtain the scattered sound fields of a general shape. This decomposition method is based on the principle that any waveform can be decomposed using a two-dimensional spatial Fourier transform into wave components that propagate in a known manner. The Cartesian method was developed by Tamara [J. Acoust. Soc. Am. 88, 2259–2264 (1990)] to measure the reflection coefficients of waves incident at oblique angles onto planar surfaces, so our paper focuses on the optimization of this method when applied to scattering investigations. A two-surface technique to separate the incident and scattered field is also developed in cylindrical coordinates. The separation process is carried out in the wave-number domain in a manner similar to what has been developed for Cartesian coordinates. However, because the incident and scattered fields are not directly separable in cylindrical coordinates, knowing general properties of the incident field make the separation process feasible. The formulation of the separation techniques and the spatial windowing and wave-number filtering needed to obtain accurate results is discussed. Numerical simulations were performed and experimental studies were conducted inside an anechoic chamber with a baffled loud speaker as the source that illuminates spheres, and a cylinder. The experiments demonstrate the feasibility of the field separation technique.
Ultrasonic characterization of heterogeneous materials using a stochastic approach
Authors: Derouiche Z. , Delebarre C. , Gazalet M. , Rouvaen J. M. , Bridoux E.
Published: October 2005

The ultrasonic nondestructive characterization of heterogeneous media is difficult due to their inherent inhomogeneity. Using high-frequency ultrasonic waves, one gets very high spatial resolutions, and the characterization of heterogeneous materials appears then feasible. However, the echographic signal processing involves a new approach, different from the classical deterministic one. Due to the random nature of the scatterers distribution, a stochastic model allows the determination of the structural parameters, like the spacings between heterogeneities (mean value and probability density function). An identification process is used to define the most convenient values for the mathematical parameters involved in the probabilistic scatterers distribution law and enables one to deduce the local concentration of scatterers. The theoretical models have been confirmed through measurements on synthetic inhomogeneous media and on two different kinds of composite materials: Metal matrix composites and carbon epoxy composites.
Segmented transducer design using an optimum mean square quantizer approach
Authors: McGehee Duncan , Jaffe Jules S.
Published: October 2005

This article describes an approach to acoustic transducer design that results in the construction of transducers with desirable radiation patterns. The radiation pattern from a uniformly excited transducer has, for many applications, unacceptably high sidelobes. A smoothly shaded transducer, e.g., one with Gaussian or Blackman-Harris shading, has better sidelobe structure but may be difficult to construct accurately. Segmented transducers, where each segment is excited uniformly, can be used to approximate a smooth shading in a stepwise fashion. The optimum mean square quantizer approach is presented in this article as a method for rationally choosing segment sizes and excitation levels. As implied by the name, the method minimizes the mean square error between a desired smooth shading and an L level segmented approximation to it. Both the sizes and the amplitude levels of the elements are allowed to vary, permitting better performance for a fixed number of elements than might be achievable for the same number of equisized elements. The method is developed in this article for two one-dimensional cases: The linear segmented transducer, and the radially symmetric segmented transducer. The method is demonstrated through the design of a three-level radially symmetric segmented transducer that generates a close approximation to a Gaussian beam.
Noise normalization technique for beamformed towed array data
Authors: Stergiopoulos Stergios
Published: October 2005

Noise normalization techniques for beamformed towed array data attempt to remove the ambient and self-noise directionality characteristics associated with the measurements in order to enhance detection of weak signals. The problem of normalization in bearing space for broadband or narrow-band plane-wave detection is similar to normalization for signal detection in the frequency domain. As a result, noise normalization techniques for the spatial domain may be modified versions of those used in the frequency domain. The aim of this paper is to develop a new concept of noise normalization for beamformed towed array data. This concept has two sets of operations; the first applies low angular and low-frequency resolution beamforming to obtain stable noise background estimates that retain the directionality characteristics of the noise field while the second includes the estimation of the geometric mean over a number of time snapshots in order to remove any high-level signal from the beam-power towed array estimates. In principle, the above set of operations have the same concept as those used in frequency domain noise normalization techniques. Their numerical implementation, however, is different. Performance analysis and comparison of the proposed normalization technique with the two-pass split-window normalizer have been carried out by using synthetic and real data sets. Although application results indicate similar performance for these two different normalization schemes, the proposed normalization method has a more efficient computational implementation and faster execution times.
Interspike intervals as a correlate of periodicity pitch in cat cochlear nucleus
Authors: Rhode William S.
Published: October 2005

Amplitude modulated (AM) signals have often been used as precisely defined partial analogs of speech sounds. This study considers the response to an AM complex with 200% sinusoidal modulation, that is, the amplitudes of the three AM components are equal. By varying the carrier frequency across the entire frequency range of unit response, it is shown that units in the cochlear nucleus of cat are relatively insensitive to variation in the carrier frequency, which is to say that population response to an AM signal at a fixed locus will be widespread. These stimuli and procedures result in the presentation of both harmonic and inharmonic complexes, and thus permit assessment of neural responses for the information needed to make spectral or time-domain pitch matches. It is shown that the reciprocals of the modes (favored intervals) in the interspike interval histogram reflect the first effect of pitch shift, which is defined psychophysically as a proportional shift in pitch to the change in carrier frequency. In particular, interspike intervals of units with a widespread spectral response provide a basis to explain phase and dominant component pitch behavior that early narrow-band pitch theories found problematical. The amplitude of phase locking to individual AM components varies systematically though there are some unexplained variations across the frequency-intensity plane that could be due to combination tones. The unit response to a quasifrequency modulated (QFM) stimulus shows that if pitch is based on interspike intervals, it would remain the same as pitch for an AM signal. The magnitude of the synchrony response to QFM stimuli is less than to AM stimuli for the majority of cochlear nucleus units; however, there are exceptions.
Effects of carrier frequency, modulation rate, and modulation waveform on the detection of modulation and the discrimination of modulation type (amplitude modulation versus frequency modulation)
Authors: Moore Brian C. J. , Sek Aleksander
Published: October 2005

Initially, psychometric functions were measured for the detection of amplitude modulation (AM) or frequency modulation (FM), using a two-alternative forced-choice (2AFC) task. Carrier frequencies were 125, 1000, and 6000 Hz, and modulation rates were 2, 5, and 10 Hz. For the two lower carrier frequencies, FM detection tended to be best at the lowest modulation rate while AM detection was best at the highest rate. For the 6000-Hz carrier, both AM and FM detection tended to be poorest at the lowest modulation rate. Then, pairs of values of AM and FM were selected that would be equally detectable, and psychometric functions were measured for the discrimination of AM from FM, again in a 2AFC task. For carrier frequencies of 125 and 1000 Hz, the ability to discriminate AM from FM was always poorest at the highest modulation rate (10 Hz); at this rate some subjects were essentially unable to discriminate AM from FM when the detectability of the modulation was relatively low (d′ of 1.16 and below). For a modulation rate of 2 Hz, and when the detectability of the modulation was moderate (d′ up to about 2), some subjects discriminated the type of modulation as well as they detected the modulation. For a carrier frequency of 6000 Hz, the effect of modulation rate varied across subjects, but there was still a trend for poorer discrimination of modulation type at the highest modulation rate.

It is suggested that FM detection at a 10-Hz modulation rate is based largely on changes in excitation level for all carrier frequencies. For a 2-Hz modulation rate, and for the two lowest carrier frequencies, an extra mechanism, possibly based on phase locking, may play a role in the detection and discrimination of FM. This mechanism may be ineffective at modulation rates above about 5 Hz because the stimuli spend insufficient time at frequency extremes. To check on this, psychometric functions were measured for the detection of FM and AM using quasitrapezoidal modulation with a rate of five periods per second and carriers of 250, 1000, and 6000 Hz. This produced improvements in performance relative to that obtained with 5-Hz sinusoidal modulation and, for the two lower carrier frequencies only, the improvements were markedly greater for FM than for AM detection. This is consistent with the idea that the use of phase-locking information depends on the time that the stimuli spend at frequency extremes.
Evaluation of a portable two-microphone adaptive beamforming speech processor with cochlear implant patients
Authors: van Hoesel R. J. M. , Clark G. M.
Published: October 2005

A two-microphone noise reduction technique was tested with four cochlear implant patients. The noise reduction technique, known as adaptive beamforming (ABF), used signals from only two microphones—one behind each ear—to attenuate sounds not arriving from the direction directly in front of the patient. The algorithm was implemented in a portable digital signal processor, and was compared with a strategy in which the two microphone signals were simply added together (two-microphone broadside strategy). Tests with the four patients were conducted in a soundproof booth with target speech arriving from in front of the patient and multitalker babble noise arriving at 90 deg to the left. Results at 0-dB signal-to-noise level (S/N) showed large improvements in speech intelligibility for all patients, when compared to the two-microphone broadside strategy. Precautions were taken to avoid cancellation of the target speech, and, accordingly, subjective tests showed no deterioration in performance for the adaptive beamformer in quiet. Physical measurement of the directional characteristics of the ABF was made with the microphones placed behind the ears of a KEMAR manikin and in the same acoustic environment as used with the patients. Results showed directional gain of approximately 10 dB when the angle of incidence for interfering noise was shifted more than 20 to 30 deg from directly in front of or behind the manikin. The effects of reverberation were explored by placing the manikin in different acoustical environments and observing the attenuation of the noise alone at various angles. A near anechoic environment allowed the noise to be attenuated by as much as 21 dB as the angle of incidence of the noise shifted away from directly in front of or behind the manikin. In a highly reverberant concrete stairwell, the adaptive beamformer was, however, unable to provide any directional gain beyond about 3 dB for any angle of incidence.
Perception of voicing for syllable-initial stops at different intensities: Does synchrony capture signal voiceless stop consonants?
Authors: Kluender Keith R. , Lotto Andrew J. , Jenison Rick L.
Published: October 2005

In response to stop consonants with longer F1-cutback duration, the dominant synchronization of mid- and high-CF chinchilla auditory-nerve fibers changes from frequencies near F2 to frequencies near F1 at onset of voicing [D. G. Sinex and L. P. McDonald, J. Acoust. Soc. Am. 85, 1995–2004 (1989)]. If this change in neural synchronization is perceptually relevant for human listeners, then it may be predicted that changes in stimulus intensity and changes in the frequency difference between lower (F1) and higher (F2/F3) stimulus components should both affect perception of voicing. In a series of experiments, multiple continua of synthesized CVs varying in F1 cutback of the consonantal portion were played to listeners at levels ranging from 40 to 80 dB SPL. Across experiments, the frequency difference between F1 and F2 was manipulated by changing the onset frequency of F1 or F2. Subjects labeled more initial stops as voiceless as a function of increasing stimulus level and of decreasing frequency difference between F1 and F2. There was also an interaction between stimulus intensity and the frequency difference between F1 and F2 such that the effect of intensity was greater for smaller differences. These effects were reliable across a number of synthetic F1-cutback series, and the effect of intensity extended to a digitally edited series of hybrid CVs in which F1-cutback was varied by cross splicing naturally produced /da/ and /ta/. The effect of overall stimulus intensity was not affected by amplitude of prevocalic aspiration energy or by the presence or absence of release bursts. The results provide evidence for the perceptual significance of synchrony encoding of voicing for stop consonants.
On the use of variable order infinite wave envelope elements for acoustic radiation and scattering
Authors: Cremers Luc , Fyfe Ken R.
Published: October 2005

The use of the variable order infinite wave envelope element to model acoustic radiation and scattering problems is investigated. Different acoustic modeling aspects are focused upon. These involve the modeling of acoustic wave propagation above infinite homogeneous impedance planes, different methods to prescribe acoustic sources and alternative postprocessing procedures. Special attention is given to limitations encountered for this finite element based modeling of wave propagation in unbounded domains. The limitations are assessed by analyzing the higher-order multipoles of the axisymmetric pulsating rigid sphere.
Sonic bands, bandgaps, and defect states in layered structures—Theory and experiment
Authors: James Richard , Woodley Scott M. , Dyer Catherine M. , Humphrey Victor F.
Published: October 2005

The propagation of sound through a one-dimensional periodic array of water and perspex plates is studied theoretically and experimentally. It is shown that the passbands and stop bands of a scatterer with a finite number of layers correspond to the bands and bandgaps of an infinite ‘‘sonic bandgap crystal.’’ The transmission coefficient of various finite structures is computed and measured as a function of frequency. The analogy with the electronic bandstructure of crystals, and the photonic bandstructure of macroscopic periodic dielectric structures, is found to be a close one. It is shown that the position and width of passbands can easily be engineered. Results are included for a finite ‘‘crystal’’ with a vacancy defect, in which a narrow passband appears in each of the stop bands.
On the Brewster wave number for the planar interface of two isotropic media
Authors: Kazandjian Luc
Published: October 2005

The case of plane-wave reflection by a planar interface joining two homogeneous, linearly elastic and isotropic solid half-spaces is considered. By using generalized reciprocity relations stemming from the time-reversal invariance of the problem equations, it is shown without explicitly solving these equations that the Brewster wave number is not dependent upon which of the two half-spaces contains the incident plane waves. Besides, the reflection factors are shown to be connected by simple relationships independent of the physical properties and of the value, real or complex, of the angle of incidence. It is indicated that these results can be extended to a large class of interfaces if the two media considered have time-reversal invariance.
Diffraction effects in nonlinear Rayleigh wave beams
Authors: Shull D. J. , Kim E. E. , Hamilton M. F. , Zabolotskaya E. A.
Published: October 2005

Nonlinear effects in Rayleigh wave beams are investigated analytically and numerically. Diffraction effects are taken into account within the parabolic approximation, and nonlinearity is taken into account with a theoretical model used previously to investigate plane and cylindrical Rayleigh waves of finite amplitude [E. A. Zabolotskaya, J. Acoust. Soc. Am. 91, 2569–2575 (1992)]. Quasilinear solutions are presented for second-harmonic generation in Gaussian beams, both unfocused and focused. Asymptotic results are derived for the second harmonic in the far field of arbitrary directive sources. Numerical solutions are used to investigate harmonic generation, waveform distortion, and shock formation in Rayleigh wave beams produced by sources with uniform amplitude distributions. Brief consideration is given to effects of source asymmetry on the radiated field.
Coupling scattering from the sea surface to a one-way marching propagation model via conformal mapping: Validation
Authors: Norton Guy V. , Novarini Jorge C. , Keiffer Richard S.
Published: October 2005

Propagation models in underwater acoustics usually incorporate sea surface scattering effects in an ad hoc manner which in most cases requires making severe approximations. In particular, to include in a coherent manner in a marching acoustic propagation model the scattering that occurs at a rough sea surface poses a serious problem. Dozier [J. Acoust. Soc. Am. 75, 1415–1432 (1984)] introduced a rigorous approach in the framework of the split-step parabolic equation model, which used a sequence of conformal mappings to flatten segments of the sea surface locally. Each conformal mapping preserved the elliptic form of the wave equation. In each transformed space the parabolic approximation is made and the solution advanced one range step. The method has the attractive feature of handling surface roughness within a propagation model in a mathematically consistent manner, including refraction and multiple surface interactions when and where they occur. In this work the technique developed by Dozier is implemented in the realm of the finite element parabolic equation model [Collins, J. Acoust. Soc. Am. 93, 1736–1742 (1993)] and applied to the problem of forward scattering from both periodic and single realizations of randomly rough surfaces. The validity of the technique is examined by comparison with an exact solution to the scattering problem obtained through the method of moments for both types of surfaces. It is shown that the current technique provides the correct energy distribution of the forward-scattered field. The performance of this hybrid model suggests that it might be well suited as the reference solution for comparing with propagation models that include sea surface scattering in a more approximate manner.
On resonance widths of leaky Lamb modes
Authors: Freedman Albert
Published: October 2005

For an elastic plate immersed in a lossless fluid, it is known that resonances of leaky Lamb modes contribute to the transmission coefficient in a manner dependent on the resonance widths. Based on numerical solutions in the complex wave-number field, an examination of such resonance widths is presented here. For plates of different materials and for water and air loadings, families of curves of Lamb mode angular resonance width versus frequency are seen to yield a consistency of pattern. For air loading, the widths are 31/2 orders smaller than for water loading. Frequency resonance widths are found to be two orders greater than angular resonance widths. Nulls in the resonance width curves provide added insight into the cause of published experimental nonobservance of radiation effects for individual Lamb modes.
Lightweight, high insertion loss, active noise enclosure with air gaps
Authors: Fuller C. R. , White C. A.
Published: October 2005

Preliminary experiments that demonstrate the control of noise using a lightweight, active enclosure with significant air gaps are discussed. The active enclosure consists of a lightweight, plexiglass box with piezoceramic actuators bonded to each side as active inputs. The control approach used is the filtered-x LMS. Global reductions of 7 to 20 dB are reported and mechanisms of control are discussed.
Critique of the ‘‘unaliased’’ discrete-time cross-ambiguity function
Authors: Pattison Tim
Published: October 2005

It is argued here that owing to an improper comparison with the ‘‘classical’’ discrete-time cross-ambiguity function (DTXAF), Bekir [J. Acoust. Soc. Am. 94, 817–826 (1993)] failed to demonstrate the alleged unaliasing property of his DTXAF.
High-frequency vibrations of liquid-filled thick elastic cylindrical shells: A simplified modal approach
Authors: Journeau Christophe
Published: October 2005

An approximate model has been developed for the high-frequency (10<Ω<100) response of liquid-filled thick elastic cylinders to a line force. Rotary inertia and transverse shear are taken into account while shell curvature is neglected. This modal approach takes into account the strong coupling between the internal pressure sound field inside the cavity and the structural motion. The results are expressed in terms of impulse response in order to show the effect on group celerity. The different types of waves (pseudo-Lamb waves, fluid waves, whispering gallery waves) are shown in the numerical results.
Inversion of the elastic parameters of a layered medium
Authors: Liu Pei-Ling , Tsai Chong-Dao , Wu Tsung-Tsong
Published: October 2005

This paper presents a method for constructing the elastic parameters of a layered elastic medium such as the wave velocities, densities, and thicknesses of the layers. The inverse problem is formulated as an optimization problem in which the norm of the discrepancies between the measured and calculated surface response is minimized. The experiments were conducted on a thin plate. The impact of a steel ball was adopted to generate a vertical point source, and an NBS conical transducer was used to record the surface response. The received signals were then processed by the layer-stripping technique to reconstruct the layer properties and thickness from the top layer down. The recovered parameters agree well with the true parameters of the specimen.
Calculating total acoustic power output using modal radiation efficiencies
Authors: Snyder Scott D. , Tanaka Nobuo
Published: October 2005

Over the last 20 years a great deal of work has been devoted to obtaining expressions describing the radiation efficiencies of structural mode shape functions, in an effort to qualify the radiation characteristics of the structure. These modal radiation efficiencies cannot, however, be used directly in the calculation of total radiated acoustic power, as this latter quantity is not equal to the sum of the acoustic power radiated by each mode vibrating on its own. This paper addressed the problem of using modal radiation efficiencies to calculate the total acoustic power output of a simply supported rectangular panel. It is shown that there is an extremely simple way to use modal radiation efficiencies to calculate the total acoustic power output of the panel, the accuracy of which is limited only by the same low-frequency constraints placed upon the accuracy of the modal radiation efficiencies themselves.
Auditory-nerve encoding of pinna-based spectral cues: Rate representation of high-frequency stimuli
Authors: Rice John J. , Young Eric D. , Spirou George A.
Published: October 2005

The elevation of sound sources and their front–back position is encoded in spectral cues produced by direction-dependent filtering in the pinna. Auditory-nerve (AN) fiber population recordings were used to analyze the neural representation of the acoustic features which carry this information. The most prominent pinna-produced spectral features occur at frequencies greater than 5 kHz, so this information must be encoded in AN discharge rates and not in measures of phase locking. However, profiles of discharge rate versus fiber best frequency (BF) reveal a poor representation of the spectra of the stimuli, primarily because of fiber-to-fiber variation in rate. The variation is not controlled by rate normalization, but a clear representation of the ratio of the magnitude spectra of two stimuli is seen when responses are plotted as the difference between the rates in response to the two stimuli. This result suggests that precise information about stimulus spectrum is present in discharge rate, which could be revealed in rate profiles constructed with suitable normalization. When binaural stimuli are presented, a weak inhibitory effect, due to the olivocochlear bundle or the middle ear muscle reflex, is observed. The rate changes are small and are not correlated with the spectrum of the contralateral ear stimulus.
Pitch matching of amplitude-modulated current pulse trains by cochlear implantees: The effect of modulation depth
Authors: McKay Colette M. , McDermott Hugh J. , Clark Graeme M.
Published: October 2005

An experiment was conducted with four cochlear implantees, which investigated the pitch evoked by amplitude-modulating current pulse trains delivered to a single cochlear location. These stimuli produce a pitch percept which may be similar to that of acoustic stimuli such as modulated noise for modulation frequencies in the range 80–300 Hz, approximately. The experiments investigated the effect of modulation depth on the way pitch was matched to that of unmodulated pulse trains. The method of constant stimuli was used, in which the variable parameter was the rate of the unmodulated stimulus. The modulated stimuli comprised pulses having one of two possible current values, with the higher value occurring once in every modulation period. The results showed that the matched rate fell exponentially from a value close to the carrier rate towards a value equal to the modulation frequency as the modulation depth increased. The results were compared to the predictions of a simple model in which the matched rate corresponded to a weighted average of carrier and modulation frequencies, with the weightings proportional to the number of neurons firing at each of these frequencies. The results agreed with the predictions of the model reasonably well, except in cases where the carrier rate was 700 Hz or higher, and for one subject at the highest intensity level.
Responses of auditory-nerve fibers to stimuli producing psychophysical enhancement
Authors: Palmer Alan R. , Summerfield Quentin , Fantini Deborah A.
Published: October 2005

A form of auditory ‘‘enhancement’’ can be demonstrated by omitting a component from a harmonic series for a few hundred milliseconds and then replacing it: the replaced component stands out perceptually. Psychophysical experiments have shown that components generate more forward masking when enhanced than when present but not enhanced. This result has been interpreted as demonstrating that enhancement involves an increase in gain in the frequency region of the replaced component. The present experiments sought physiological evidence of enhancement in the responses of auditory-nerve fibers in the guinea pig. In one condition a 200-Hz harmonic series lacking components near 2 kHz preceded another series with the 2-kHz component present (the ‘‘test’’ series). In this condition the mean discharge rate to the 2-kHz component was larger than the adapted responses to the other components of the test. In a second condition the test series was preceded by silence. In both conditions the 2-kHz component caused the same increase in firing rate. The average discharge rate sychronized to the 2-kHz component was also the same in both conditions. However, the proportion of the total discharge rate which was locked to 2 kHz was larger when the test followed the harmonic series than when it followed silence. Thus the contrast, in terms of both mean and synchronized rates, between the responses at 2 kHz and those at other frequencies, was increased when the test was preceded by the harmonic series. However, there was no evidence of an increase in gain (i.e., absolutely larger responses) in the 2-kHz region. It seems likely therefore that the mechanisms responsible for this aspect of auditory enhancement are located more central than the auditory nerve.
The role of envelope fluctuations in spectral masking
Authors: van der Heijden Marcel , Kohlrausch Armin
Published: October 2005

Two experiments are reported in this study. In the first experiment the masking effect of five different types of narrow-band maskers was compared. The masker was either a tone, a narrow-band Gaussian noise, or a multiplication noise obtained by multiplying a sinusoid with a low-pass Gaussian noise. The noise maskers had a bandwidth of either 20 or 100 Hz. In all cases the masker had a center frequency of 1.3 kHz and a duration of 500 ms. Five-point growth-of-masking functions were measured using a 2-kHz tonal target with a duration of 400 ms, temporally centered in the masker. Six subjects participated in the experiment. Although considerable intersubject differences were observed, the data of all subjects showed several common trends. First, the tonal maskers produced more masking than the noise maskers. Second, Gaussian noise maskers produced more masking than multiplication noise maskers of the same bandwidth. Finally, 100-Hz-wide noise maskers produced more masking than 20-Hz-wide maskers of the same type. Differences in masked thresholds between the various masker types generally increased with masker level, and exceeded 25 dB in some conditions. The results are discussed in terms of masker envelope fluctuations. In the second experiment the masking effect was investigated for a bandpass noise at 1.3 kHz, with regular zero crossings, but with the envelope characteristics of a 100-Hz-wide Gaussian noise. Five-point growth-of-masking functions were measured using a tonal target of 2 kHz. Masked thresholds produced by this hybrid masker were not significantly different from those produced by a 100-Hz Gaussian masker, but differed significantly from those produced by 100-Hz-wide multiplication noise. This result indicates that differences in masking between Gaussian and multiplication noise are not due to their different fine structure, but to their different envelope statistics.
Incomplete compensation to articulatory perturbation
Authors: McFarland David H. , Baum Shari R.
Published: October 2005

Measurements were made of vowels, fricatives, and stop consonants produced by 15 adult speakers of French in one free-mandible and two fixed mandible conditions. Speech acoustic data were recorded immediately upon bite-block insertion and after a 15-min accommodation period. Results indicate that compensation to increased jaw opening during speech is neither immediate nor complete as there were small but significant differences in the acoustic parameters of vowels and consonants produced under bite-block and normal conditions. Further, the data suggest that, at least for vowels, speech compensatory strategies may develop over time, perhaps involving error-based correction. Consonants appear to require a more lengthy period of speech adaptation, and this may be due to the articulatory requirements for their accurate production. Individual differences in compensatory abilities are also discussed.
Bifurcations in an asymmetric vocal-fold model
Authors: Steinecke Ina , Herzel Hanspeter
Published: October 2005

A two-mass model of vocal-fold vibrations is analyzed with methods from nonlinear dynamics. Bifurcations are located in parameter planes of physiological interest (subglottal pressure, stiffness of the folds). It is shown that a sufficiently large tension imbalance of the left and right vocal fold induces bifurcations to subharmonic regimes, toroidal oscillations, and chaos. The corresponding attractors are characterized by phase portraits, spectra, and next-maximum maps. The relevance of these simulations for voice disorders such as laryngeal paralysis is discussed.
Vocal efficiency as a function of vocal intensity: A study of children, women, and men
Authors: Tang Junnong , Stathopoulos Elaine T.
Published: October 2005

The effect of vocal intensity on vocal efficiency (VE) for children as compared to adults is investigated, leading to the conclusion that children have different VE values than adults. Vocal efficiency was measured using a logarithmic form of the ratio of the acoustical power radiated from the lips to the aerodynamic power supplied to the glottis for voice production. Sixty subjects participated in this study, including 20 subjects with 10 males and 10 females in each of the three age groups: 4-year-olds, 8-year-olds, and adults. The speech tasks were produced at soft, comfortable, and loud levels, and the VE measurements were mathematically adjusted to account for the sound-pressure level variations within each intensity level among the subject groups. The VE values were compared for age, intensity, and gender differences. The results indicate that 4-year-olds and 8-year-olds have lower VE values than adults. Vocal efficiency increased with vocal intensity for all the age groups, and no significant differences were found for females as compared to males. Factors influencing VE such as maturation of the vocal ligament, amplitude of vocal fold vibration, fundamental frequency, tracheal pressure, as well as the source spectra are discussed.
Automatic recognition of syllable-final nasals preceded by /ε/
Authors: Loizou Philipos , Dorman Michael , Spanias Andreas
Published: October 2005

In this paper, it is shown how an automatic recognition algorithm, based on hidden Markov models (HMM), can benefit by properly utilizing findings from perceptual experiments on nasals. Perceptual studies on nasal consonants have shown that both nasal murmurs and formant transitions are important in the identification of place of articulation. Thus both acoustic segments bordering the nasal release were incorporated into this HMM-based system. A 7% improvement in alveolar recognition was obtained by explicitly modeling the vowel-nasal transition segments. Further overall improvement (6%) was realized by making the HMM recognizer ‘‘focus’’ more on the vowel-nasal transition segments bordering the nasal release, and less on the nasal murmur and vowel portion of the /ε m/ and /ε n/ syllables. An overall average [m]–[n] recognition of 95% was obtained when testing this technique on 60 speakers outside the training set.
Acoustical behavior of brass player’s lips
Authors: Yoshikawa Shigeru
Published: October 2005

The controversial problem of whether a brass player’s lip movements are best modeled as outward striking or as upward striking is approached by measuring the phase difference between mouthpiece pressure and lip displacement. In analogy with the phase of the input impedance to a resonant system, the negative/positive value of this phase difference suggests an outward-striking/upward-striking oscillation. On the basis of this speculation, the experimental results revealed the following: (1) Large lip-driven pipes support both outward-striking and upward-striking oscillations because of the lip’s high flexibility in the absence of a mouthpiece; (2) mouthpiece-nonresonant tube systems almost support the outward-striking oscillation over a wide frequency range; (3) mouthpiece-resonant tube systems totally support the outward-striking oscillation; (4) the French horn and trumpet exhibit the outward-striking oscillation for the lowest mode and the upward-striking oscillation for higher modes. The oscillation transition in brass instruments, which corresponds well to the change of mouthpiece pressure waveform from a low-pitch, nonsinusoidal one to a higher-pitch, more sinusoidal one, depends mainly on the nonlinear acoustic impedance of the lip opening. If its magnitude is negligible, the cavity coupling between the mouthpiece cup and player’s mouth yields a capacitive input impedance that favors the outward-striking oscillation; if its magnitude is significant, the cavity decoupling is likely to yield an inertive input impedance that favors the upward-striking oscillation. Since both the time-varying Bernoulli pressure at the lip opening and the area receiving this pressure are generally apt to increase as the blowing pressure increases, the upward-striking oscillation tends to dominate higher mode tones in brass instruments.
The kinematics of musical expression
Authors: Todd Neil P. McAngus
Published: October 2005

The notion that there is an intimate relationship between musical motion and physical movement is an old one and can be traced back to antiquity. Recently this idea has again received some attention, particularly in relation to musical expression. To use a modern metaphor, one can consider expressive performance to be analogous to the problems of kinematics and trajectory planning in robotics. The trajectories referred to, however, are not those of the performers limbs in physical space, but those of an abstract movement relative to a metrical grid associated with a musical score. Recent studies have attempted to substantiate this idea by comparing a model of motion with timing measurements of the final ritardandi from actual performances. This study extends these earlier analyses to include the accelerandi as well as the ritardandi from complete performances. One conclusion is that the variation of tempo in music can be reasonably compared with velocity in the equations of elementary mechanics. Further, it is suggested that the origin of metrical space, upon which the motion concept rests, lies in the way the auditory system processes rhythm.
Measurement and correction of ultrasonic pulse distortion produced by the human breast
Authors: Hinkelman Laura M. , Liu Dong-Lai , Waag Robert C. , Zhu Qing , Steinberg Bernard D.
Published: October 2005

Ultrasonic wavefront distortion produced by transmission through breast tissue specimens was measured in a two-dimensional aperture. Differences in arrival time and energy level between the measured waveforms and references that account for geometric delay and spreading were calculated. Also calculated was a waveform similarity factor that is decreased from 1.0 by changes in waveform shape. For nine different breast specimens, the arrival time fluctuations had an average (±s.d.) rms value of 66.8 (±12.6) ns and an associated correlation length of 4.3 (±1.1) mm, while the energy level fluctuations had an average rms value of 5.0 (±0.5) dB and a correlation length of 3.4 (±0.8) mm. The corresponding waveform similarity factor was 0.910 (±0.023). The effect of the wavefront distortion on focusing and the ability of time-shift compensation to remove the distortion were evaluated by comparing parameters such as the −30-dB effective radius, the −10-dB peripheral energy ratio, and the level at which the effective radius departs from an ideal by 10% for the focus obtained without compensation, with time-shift estimation and compensation in the aperture, and with time-shift estimation and compensation performed after backpropagation. For the nine specimens, the average −10-dB peripheral energy ratio of the focused beams fell from 3.82 (±1.83) for the uncompensated data to 0.96 (±0.18) with time-shift compensation in the aperture and to 0.63 (±0.07) with time-shift compensation after backpropagation.

The average −30-dB effective radius and average 10% deviation level were 4.5 (±0.8) mm and −19.2 (±3.5) dB, respectively, for compensation in the aperture and 3.2 (±0.7) mm and −22.8 (±2.8) dB, respectively, for compensation after backpropagation. The corresponding radius for the uncompensated data was not meaningful because the dynamic range of the focus was generally less than 30 dB in the elevation direction, while the average 10% deviation level for the uncompensated data was −4.9 (±4.1) dB. The results indicate that wavefront distortion produced by breast significantly degrades ultrasonic focus in the low MHz frequency range and that much of this degradation can be eliminated using wavefront backpropagation and time-shift compensation.
An acoustic basis for maternal recognition in timber wolves (Canis lupus)?
Authors: Goldman J. A. , Phillips D. P. , Fentress J. C.
Published: October 2005

An in-den recording system was used to monitor the vocalizations and behavior of adult wolves tending to a litter of pups during the first five postnatal weeks. Two female adults, one of them the mother, tended to the pups on nonoverlapping schedules. The distributions of the fundamental frequencies of the adults’ squeak vocalizations were largely nonoverlapping, suggesting that this feature may be available as an acoustic cue to individual recognition. Squeaks emitted outside the den, and which were associated with pup exit responses, had fundamental frequencies wholly within the range of the mother’s, raising the possibility that the pups used this as a cue for maternal recognition.
Sound propagation in dilute gas–liquid suspensions: Definition of the regime of noninteracting bubbles via scattering theory and the causality approach
Authors: Leander Johan L.
Published: October 2005

In this letter sound propagation in gas–liquid suspensions from two different perspectives, i.e., scattering versus nonscattering theories, is examined. The purpose is to analyze limitations of the different approaches while considering the case of dilute suspensions where there is no acoustic interaction between the bubbles. By means of single-scattering theory the transmission can be modeled as a plane wave exhibiting attenuation and dispersion provided the propagation length is limited. This requirement is usually not evident in nonscattering models. However, it is shown here that by use of the causality approach, one can obtain an analogous limitation concerning the propagation length that appears in the study of sound propagation in dilute suspensions via scattering theory. Thus the restriction is found also by means of a nonscattering approach.
Normal-mode propagation in slowly varying ocean waveguides
Authors: Desaubies Yves , Dysthe Kristian
Published: October 2005

Acoustic propagation in a slowly varying ocean waveguide can be represented by a set of propagating modes. It is shown that for general slowly varying ocean waveguides, normal modes can be defined in the usual sense of classical mechanics: Normal modes are described by independent differential equations and do not exchange energy. Such modes have also been called intrinsic modes. The derivation is a perturbation method based on the existence of a small parameter ε characterizing the horizontal rate of variation of the waveguide. The expansion is analogous to the Rytov approximation of wave propagation in random media. Uncoupled normal modes (intrinsic modes) are found as perturbation of the local modes. The first-order result is a depth-dependent phase change such that each mode conserves its energy flux as it propagates. An equivalent result is obtained by introducing a nearly orthogonal curvilinear coordinate system in which the Helmholtz equation is separable. The terms of the next order (ε2) show that at this order there is still no coupling. The two solutions are equivalent, and reduce to the exact solution for the wedge problem. Coupled- (local) mode theory is also recovered by doing the proper expansion in the small parameter ε. Comparisons are made with the numerical solution of the ASA benchmark problems. The approximate normal modes effectively sum the terms due to coupling and demonstrate that the concept of coupled modes, with its implication of energy exchange, can be misleading.
The influence of pressure ridges on seismic signals due to thermal cracking of sea ice
Authors: Xie Yunbo , Farmer David M.
Published: October 2005

Thermal stress can fracture sea ice resulting in the radiation of both acoustic energy into the water and seismic waves in the ice. However, the distribution of seismic energy is strongly modified by the presence of pressure ridges which attenuate flexural waves. Observations of thermal stress cracks with an array of geophones and hydrophones on land-fast first-year ice provide an opportunity for evaluating this effect. The acoustic measurements allow precise positioning of individual fractures and the geophones allow measurement of the seismic signals. Few of the events occurring behind a pressure ridge result in detection of significant flexural wave energy, whereas most sources at equivalent range without an intervening pressure ridge have strong seismic signals. Attenuation by the ridge is explained with a flexural model of a plate which also includes a change in thickness and porosity representing the pressure ridge.
Flexural waves in a floating ice sheet: Modeling and comparison with data
Authors: Yang T. C. , Yates T. W.
Published: October 2005

Ice vibrations caused by a vertical impulse force are calculated in this paper using fluid-loaded thin elastic plate theory. The plate response is calculated in the frequency domain, multiplied with the source spectrum and inverse Fourier transformed to obtain the time domain solution. The time domain solution is compared with the vertical-axis geophone array data collected in the Arctic on a smooth ice floe using a vertical hammer strike as the source. The model, assuming a linear frequency dependence in ice attenuation, provides a reasonably good fit to the spectral densities as a function of distance for three bands of frequencies. The modeled waveforms along the array of receivers matches reasonably well with the data. Frequency-wave number analysis is applied to the modeled time series as was done for the data. Overall good agreement was found between the modeled and measured frequency dispersion curves but the model could not account for the splitting of the frequency dispersion seen in the data. The forced and free-wave components excited by a point versus a line force are examined and comments are made on the experimental implications for ice attenuation measurement and inverse source determination.