bluuebunny/crossref_metadata_2025 huggingface dataset:
“Log-abnormal” distributions
Authors: Maples Louis C.
Published: October 2005

Because of their being normally measured on a logarithmic scale and expressed in decibel notation, many acoustic quantities such as pressure, power, and intensity seem to have a dual existence, in linear space as basic physical variables, and in log or dB space as parameters in the sonar equations. Although not all of us are comfortable with evaluation of basic statistics in log space, lack of linear experimental values, and the large dynamic ranges involved, make it difficult to cope with the problem of sample interval without losing trees in forest, and determination of distribution/density functions in linear space is sometimes impracticable. It seems therefore advisable at least to consider the distribution question in dB space. Accordingly, experimental and model data on parameters including ambient noise, propagation loss, bottom loss, and scattering have been studied, distribution curves developed, and moments characterizing the distributions calculated. As a result of these studies it is suggested that the distribution functions, although not necessarily analytical, may be used, not only for evaluation of experimental determinations of acoustic parameters, but as measures of model validity.
Resonances in acoustic bottom reflection and their relation to the ocean bottom properties
Authors: Nagl A. , Überall H. , Hoover W. R.
Published: October 2005

The acoustic reflection coefficient of the ocean bottom plotted versus frequency or angle often exhibits a complicated structure of peaks and dips. Features as these may be attributed to resonance phenomena, and the resonance structure, i.e., the distribution and the widths of the resonances, is found to contain essentially all relevant information about the interacting medium. Interpreting the reflection coefficient as a series of antiresonances and applying our previous resonance formalism (i.e., approximating the exact form of the resonant amplitude by Breit-Wigner resonance shapes), one finds a direct link between measurable quantities (locations and widths of resonances) and medium properties, thus enabling us to solve the inverse scattering problem. We demonstrate this approach by the example of a liquid layer imbedded between two different liquid, semi-infinite media. We then show explicitly the connection between the resonance data and the medium properties (densities, sound speeds, and layer thickness). For realistic models of the ocean floor, additional features (shear wave propagation, attenuation, density, and velocity gradients) must be included. The implication of this on the formalism will be discussed.
Alternative noise certification concepts for air carrier aircraft
Authors: Sutherland Louis C.
Published: October 2005

This paper examines a number of general and specific concepts in noise certification. These include current takeoff and landing flight procedure requirements, and the potential role of static engine noise testing for noise certification. Effectiveness of existing noise certification concepts are briefly reviewed and alternative methods considered which stress measures of total community-noise impact. The most interesting of the certification procedures considered consisted of two elements: (1) an initial static engine/nacelle test to certify an engine for the absence of significant pure-tone components or to provide measured data, when required, to cover an acoustical change involving only the engine/nacelle combination, and (2) a level flyover test to certify an aircraft for noise after translation of the measured data to fixed measurement points on the ground under maximum noise flight conditions. For the latter tests, maximum gross weight is still recommended as the aircraft performance parameter to use for determining acceptable noise levels. However, the current two-value takeoff certification requirement might be replaced by the average of these two quantities as a single takeoff noise certification value. [Work supported by FAA.]
Environmental noise assessment, Sherman, Texas
Authors: Putnicki George J.
Published: October 2005

The environmental noise assessment was conducted in Sherman, Texas, in March 1980, using students from two University of Texas at Dallas graduate classes and four undergraduate classes from Austin College. The methodology used was designed to provide municipal authorities with environmental noise data sufficiently accurate to support specific municipal programs and for general municipal planning uses. Forty-two sites were selected in various land-use zones to obtain acoustical and source identification data. American National Standards Institute, type 1 sound-level meters were used to obtain 30-min interval data during week day and night and weekend day and nighttime hours. The 24-h day-night average sound levels were computed for each of the 42 sites and compared to the identified levels and standards established by the Federal agencies with environmental noise abatement and control responsibilities. The acoustical data obtained indicated that the levels in the noise-sensitive land-use ares were within the identified levels and standards established by EPA, HUD, and FHWA. The most prevalent sources were automobiles, trucks, and motorcycles.
Effect of hearing protectors on thresholds of machinery cues in noise (Experiment 1: Naive subjects)
Authors: Lambert David R.
Published: October 2005

The effect of hearing protectors on the masked threshold of specific shipboard machinery sounds (cues) in several kinds of shipboard background noise was investigated in a laboratory experiment. On the average, hearing protectors raised the masked threshold. The amount of this decrease in sensitivity depended upon the specific cue, the type of background noise, and the individual subject. [Work sponsored by the Naval Sea Systems Command.]
Modification of electrostatic headphones for electrophysiological investigations
Authors: Talkin David , Heinz John , Resnick Steffi
Published: October 2005

Investigations which require measurement of auditory-evoked potentials at the human scalp typically require acquisition and averaging of submicrovolt signals. Stimulus-related electric and magnetic fields present in the vicinity of the recording electrodes induce potentials which add to and frequently confound observation of the electrophysiological response of interest. This effect is especially troublesome when the stimulus duration is greater than the response latency. Use of a remote transducer operating in free field or through an acoustic transmission line avoids the stimulus artifact but reduces experimental control of the acoustic stimuli. This paper describes modification of a set of commercially available electrostatic headphones (Koss ESP-9). The modified phones are shown to produce a minimal stimulus artifact while maintaining the acoustic characteristics of the original ESP-9 phones. The capabilities and limitations of the modified phones in the context of psychoacoustic and electrophysiological experimental situations will be discussed. [Work supported in part by Biomedical Research Support Grant (RR-05808) to John F. Kennedy Institute: NIH.]
Comprehensive measurements of the characteristics of compression hearing aids
Authors: Burnett Edwin D. , Beck Lucille B.
Published: October 2005

Current standardized methods for the measurement of hearing-aid performance (Specification of Hearing Aid Characteristics, S3.22-1976, American National Standards Institute, New York) call for the measurement of two special characteristics of compression hearing aids, namely the dynamic and input-output characteristics, at 2 kHz. A more thorough characterization of compression hearing aids requires measurements at more than one volume-control setting to determine if the compression is controlled by the input or output signal. Also useful are random-noise transfer functions and transmissibility measurements to determine the response to multifrequency signals, input-output characteristics at several frequencies to determine the compression behavior in various frequency bands, and correlation coefficients to examine the influence of nonlinearities and internal noise in the hearing aid upon its performance. Measurements of these parameters are shown at two volume-control settings for several commercially available hearing aids and their general applicability is discussed. [Work supported by the Veterans Administration.]
Evaluation of acoustic parameters of audiometers
Authors: Benwell D. A.
Published: October 2005

Investigations of the accuracy of audiometers sold in Canada were made by measuring their acoustic signals. Fourteen new audiometers were tested, all different models, consisting of 12 screening audiometers (including one automatic model) and 2 clinical audiometers. In Canada there is a voluntary standard for new audiometers, and audiometric calibration is most frequently conducted by the manufacturer. Thus the accuracy of audiometers depends mainly on the manufacturer. The results of our tests showed that systematic errors occur in some audiometers, although all are close to meeting the requirements of the Canadian voluntary standard. Test results are presented and the difficulties encountered in some of the test measurements are described. Five of the audiometers tested had attenuators which appeared to be nonlinear at hearing levels less than 20 dB. Zero dB hearing level measurements could not be made on all audiometers due to an apparent coupling effect between the audiometer earphone and our artificial ear.
A microprocessor-based real time data acquisition system for study of acoustically excited flow fields
Authors: Walker Bruce E. , Charwat Andrew F. , Olch Ronald H.
Published: October 2005

The data-acquisition chain described in this paper allows mapping out the structure of flows generated by the interactions of high intensity sound with boundary layers in high-speed flow, specifically, the nearfield over the orifice of a Helmholtz resonator in grazing flow. Some of the stringent requirements which had to be met were: (a) local measurement at approximately 600 locations of the instantaneous vector velocity in four quadrants, accurately phased to the excitation; (b) signal recovery from the noise level of the turbulent flow; (c) signal processing without approximation of the complex instrument transfer functions; (d) on line monitoring and correction for drift during the 15-h continuous run. The microcomputer “actively” participates in the process. It generates the excitation, positions the probes, reads the outputs of two split-film CT anemometers and two microphones 64 times per cycle at 100 Hz, reduces them to velocity and angle data by look up in calibration tables stored in memory, conditionally averages data at constant phase over approximately 5000 cycles to reject uncorrelated turbulence and stores the results on magnetic disks. [This research was sponsored by NASA-Lewis Research Center.]
Description of a computerized system for analysis of reverberation time, STC and IIC
Authors: Brack Michael
Published: October 2005

The computer of an FFT system was interfaced to a 13-octave band real-time analyzer to reduce analysis time of tape recorded data as well as increase accuracy. Some of the programs developed for this system are described. These include a reverberation-time analysis program which allows time averaging of decays for each 13-octave band from 100 Hz to 5 kHz simultaneously, and displays the decays on a CRT. An operator can then select for each 13-octave band any portion of the decay, by means of cursors, on which a straight-line, least-squares curve fit is performed to determine the reverberation time. The time-averaged decays can be plotted on a digital plotter in order to examine double slopes or other decay characteristics in detail. Other programs developed include those for determining the space-average SPL in a room from a moving microphone, the results of which are stored in a file on magnetic disk. The stored spectra, reverberation times and appropriate room dimensions are then used by other programs to determine transmission loss and STC or normalized SPL and IIC. These values along with STC or IIC contours can be plotted directly with appropriate labels for inclusion in a report.
Improved piezoelectric transducers for acoustic emission signal reception
Authors: Proctor Thomas M.
Published: October 2005

Faithful transduction of the surface displacement due to acoustic emission (AE) is essential to the success of recognizing an AE source. A piezoelectric transducer has been designed and developed that has promise of being a hi-fi AE transducer. Small transducer contact area, elimination of acoustical interference associated with coherent geometries and dimensions, and removal of most of the back reflections were guiding criteria in the design. Unlike the usual commercial AE transducer this design is simple in construction having only two parts. It consists of the active element and a backing. Tests have been made using surface wave seismic-type signals associated with a point force step function. Transducer performance has been compared with the response of the line-type capacitance standard transducer used by the National Bureau of standards acoustic emission calibration. These improved piezoelectric transducers tend to have a response which increases slightly with frequency over the range of 30 kHz to 1.2 MHz with a total variation in response for this range of less than 5 dB.
On the development of a glass fiber composite flextensional transducer
Authors: Brigham G. A. , Marshall W. J. , Rynne E. F. , Nichols C. S.
Published: October 2005

The need to minimize size and Weight of resonant, low-frequency, underwater transducers directs exploiting materials relatively new to transducer technology. Since the electroacoustic characteristics of flextensional transducers are strongly dependent on both elastic modulus and density of the transducer's outer shell, the possibility of having a significant impact on transducer size by use of low density, low sound speed materials occurs. Some of the more attractive materials for this purpose are filament-wound fiber reinforced epoxies because of their low pc coupled with high strength. An experimental program is being conducted at Sanders, under NOSC support, to develop a low-frequency, wide-band, high-power flextensional transducer using high strength E-glass/epoxy resin composite shells. This paper is a summary of the design, application, and performance of the first test modules from this program, including both shell strength and electroacoustic data. Extrapolations to other frequencies, bandwidths and depth requirements are also included. [Research supported by contract N000123-79-C-0554.]
Radiating head flexure and its effect on transducer performance
Authors: Butler J. L. , Cipolla J. R. , Brown W. D.
Published: October 2005

The design requirements of underwater sound transducers often lead to a radiating head structure that exhibits flexure at a frequency close to the transducer's fundamental resonance. An analysis of this flexure is presented along with a comparatively simple model that can be incorporated into many transducer element and array interaction design programs. Results are presented for a particular case to illustrate the physical effects and also the advantages (such as a reduction in the fundamental resonant frequency) and disadvantages (such as reduced performance above resonance) that are a consequence of flexural head motion.
Discriminant analysis of the acoustics of seven English voiceless fricatives
Authors: Krieg Laurence J. , Benson Peter J.
Published: October 2005

The analysis of fricatives has typically been either acoustic (by spectroscopy and analysis-by-synthesis) or perceptual (by multi-dimensional scaling of responses to natural stimuli and bivariate analysis of responses to specially prepared stimuli). While these contribute to our knowledge, there are too many possible acoustic cues within the speech signal to be accounted for in an economical way. Further, of the English voiceless fricatives, only [f θ s ∫] have been studied extensively; the three fricative-like sounds [h ʍç], occurring at a systematic phonetic level in many English dialects, have been largely neglected. The present study used multiple discriminant analysis to find the most effective acoustic cues for discriminating and characterizing phonologically all seven English voiceless fricatives. Acoustic information was extracted digitally using several techniques whose relative effectiveness was then compared. The most successful measures were the quartiles of spectral energy distribution, expressed in mels; VOT; and the peak amplitude of the fricative relative to the peak of the neighboring vowels. Three discriminant functions were found to account for 98.5% of the variance; posterior classification was successful in 90% of the samples.
Spectral features as cues to place of articulation in stop consonants
Authors: Kewley-Port Diane
Published: October 2005

After some thirty years of research aimed at identifying invariant acoustic cues to specify place of articulation in stop consonants, S. E. Blumstein and K. N. Stevens [J. Acoust. Soc. Am. 66, 1001–1017 (1979)] claim to have solved the problem. They matched specific templates to a single 26-ms spectrum located at the burst release. This study employing spectrally changing displays is an extension of research previously reported before the Society. Place of articulation is identified from LPC running spectral displays offset at 5-ms intervals. Place is judged visually using three features with acoustic properties similar to Blumstein and Stevens', but involving spectral change. Displays contained the syllables /b, d, g/ before eight vowels pronounced by three talkers. Judges correctly identified 88% of the consonants from the running spectral displays. Identification was better for the male talkers (92%) than the one female talker (78%). The nature of the information contained in running spectral displays was also analyzed to take into account known properties of filtering of speech by the human auditory system. The advantages of dynamic running spectral displays of speech incorporating known psychophysical properties of the auditory system, including spectral change over time and auditory filtering, will be discussed with regard to the static template matching approach advocated by Blumstein and Stevens. [Supported by NINCDS Grant NS-12179.]
Parameterization of the glottal source function and glottographic waveforms
Authors: Titze Ingo R.
Published: October 2005

A five-parameter representation of glottal and glottographic waveforms is proposed. Parameters consist of amplitude, period, open quotient, symmetry (speed) quotient, and an exponent of a trigonometric function that governs the sharpness of closure. A compact mathematical formula, based on a nonlinearly distorted sinusoid, is proposed for synthesis. It produces a variety of functions, ranging from idealized square, sawtooth, and sinusoidal waveshapes to more complex truncated and skewed pulses. The effects of each parameter on the waveshapes and spectral envelopes are demonstrated. Sharpness of closure determines the spectral slope, symmetry quotient is related to the amplitude of the spectral ripple, and open quotient is related to the periodicity of the ripple. Strategies for automatic picking of the parameters are suggested for analysis of glottographic waveforms.
A study of the space and time stability of a narrow-band long-range acoustic signal in the ocean
Authors: Browning D. G. , Herstein P. D. , Koenigs P. D.
Published: October 2005

A study is made of the stability of the principal parameters of a narrow-band acoustic signal transmitted over a long range to a field of receivers. Measurement is made of the center frequency, bandwidth, and peak intensity as a function of both space and time. The relative stability of each parameter is determined and the possibility of identifying a single disturbance event is discussed.
Analytical modeling of noise transmission into aerospace vehicles
Authors: Wilby J. F. , Pope L. D. , Rennison D.C. , Wilby E.G.
Published: October 2005

The development of analytical models to predict noise transmission into aerospace vehicles has been the subject of several recent studies. The basic approach followed in the analysis is the power flow method whereby acoustic power inflow is balanced by the sum of the power outflow and power dissipation within the vehicle. Prediction of the vibration of, and acoustic radiation from, the transmitting structure are essential components of the analytical model both at low frequencies, where modes have to be considered on an individual basis, and at high frequencies, where averaging techniques such as statistical energy analysis can be used. Structural parameters such as resonance frequencies, modal characteristics and damping are required. Two applications—payload bay of the Space Shuttle orbiter vehicle and interior of a propfan-powered aircraft—are discussed. For the case of the Space Shuttle, examples are given of validation tests and subsequent modifications to assumptions in the analytical model required to improve prediction accuracy.
Automation of the fringe-disappearance method for calibrating vibration pickups
Authors: Serbyn M. R. , Payne B. F.
Published: October 2005

The classical fringe-disappearance method of optical interferometry was incorporated into an automated system for calibrating vibration pickups. The new feature of the technique is the ability to set the vibration level corresponding to a fringe-disappearance condition by an algorithm. For this purpose only the dc component of the photodetector output needs to be monitored. The complete system includes a Michelson interferometer, a minicomputer, and a digital voltmeter. Measurements of acceleration sensitivity performed by this method are compared with the results obtained by other techniques. Factors affecting the accuracy and precision of the new method have been investigated, and are discussed in considerable detail.
Deep-ocean acoustical effects of depth-varying source motion at short ranges
Authors: Kays J. L. , Jacobson M. J. , Siegmann W. L.
Published: October 2005

Ray theory is applied to a cw signal transmitted through a deep-ocean channel, and the combined effects of vertical and horizontal source motion are examined for ranges up to 10 km. Numerical computations, valid for suitably limited time intervals, are used to show the temporal variations in the multipath arrival at a point receiver fixed on the surface. Source motion is taken to be a constant-speed, linear path above the SOFAR axis. General analytical expressions, which closely approximate numerical results, are derived and used to study a pseudo-Doppler frequency shift in terms of source-motion parameters and horizontal source-receiver range. It is shown that strictly horizontal motion induces a virtually constant total-field phase rate, which is proportional to both source speed and range. However, the introduction of variations in source depth generates regularly spaced, brief changes in phase. These changes, accompanied by large amplitude fades, occur with a period which is virtually proportional to vertical speed and range, but are unaffected by source depth and horizontal speed and direction. [Work supported by ONR.]
Intensity discrimination with signal and masker uncertainty
Authors: Speigel Murray F. , Green David M.
Published: October 2005

Studies of the detection of tones in noise show little effect of signal-frequency uncertainty. We used multi-tone maskers, consisting of n(n = 1 to 20) components selected from a set of 200 sinusoids. The signal is an increment on one of the components. Either the signal's frequency or the n components selected as the masker, or both, were randomly determined on each trial of a two-alternative forced-choice task. The results show uncertainty about the set of maskers can have a greater effect than does signal uncertainty. Apparently it is easier to monitor a number of fixed frequencies for a single, randomly chosen, increment than to listen for an increment at a single frequency when the other masker frequencies change at random. In other experiments the level of the entire masker was randomly attenuated within trials. The results are consistent with the hypothesis that the intensity discrimination process can compare levels across critical bands and hence lessen the effects of uncertainty. [Work supported by NIH.]
The enhancement effect and forward masking
Authors: Viemeister Neal F.
Published: October 2005

The audibility of a given target frequency in a spectral complex can be markedly increased by exposure to the complex with the target frequency deleted. This “enhancement effect” can be observed under a wide variety of conditions and presumably reflects frequency-specific adaptation: the frequency region around the target frequency is not adapted during the exposure and hence is relatively more sensitive. The immediate question is whether the increase in relative sensitivity reflects a reduction in masking of the target frequency due to a decrease in the effective level of components in the exposure complex, or whether the sensitivity or “gain” in the unadapted region is increased. The present study addresses this question by comparing the forward masking produced by an “enhanced” tone (a 2-kHz component in an equal-amplitude harmonic complex) with that produced by unenhanced tones. Approximately 8 dB more forward masking is produced by an enhanced tone than by that component in isolation or by the spectral complex when the tone is not enhanced. An enhanced tone thus behaves as if it were physically more intense. This surprising result suggests that adaptation by the exposure complex produces an increase in gain in the unadapted frequency region. [Supported by NIH grant NS12125.]
Acoustic radiation by finite shells
Authors: Gerges Samir N. Yousri , da Silva Pinto Jorge C.
Published: October 2005

A knowledge of the radiated acoustic power is required in estimating the coupling between a sound field with a vibrating structure, and to include acoustic damping in the analysis of structure vibration. In this paper the acoustic power radiated by a finite vibrating length of an infinite cylindrical shell which vibrates in axial and circumferential directions has been theoretically analyzed. A single integral equation for the radiation efficiency of a single vibrational mode of the finite shell is obtained. A close form solution is obtained at low frequencies. Precise numerical integration provides curves covering the entire frequency range and confirming the close form solution for the low- and high-frequency limits. The objectives of this paper is to present accurate data for the radiation efficiency of finite shells and to complement data published for other type of structure such as beams [S. N. Yousri Gerges and F. J. Fahy, J. Sound Vibration 26, 437–439 (1973); and 4, 299–306 (1975); also C. E. Wallace, J. Acoust. Soc. Am. 51, 936–945 (1970)] and panels [C. E. Wallace, J. Acoust. Soc. Am. 51, 946–952 (1970); and M. C. Gomperts, Acustica 30, 320–323 (1974)]. Results obtained show that below the critical frequency, the radiation efficiency falls exponentially with frequency depending on length to radius ratio and mode numbers. Around the critical frequency the variation of the radiation efficiency with respect to frequency and shell parameters is not simple monotonic because complicated interference effects between waves and the shell occur. Above the critical frequency the radiation from finite shell asymptotically approaches that from an infinite shell, and well above the critical frequency approaches unity. [CNPq, CNEN, and FINEP in Brasil are gratefully acknowledged.]
Acoustical properties of heterogeneous viscoelastic materials at ultrasonic frequencies
Authors: Madigosky W.
Published: October 2005

The results of numerous measurements of the velocity of sound for longitudinal acoustic waves in solid heterogeneous materials are presented with viscoelastic (rubbery) materials as the base and various concentrations of inclusions distributed throughout. Used for the inclusions were lead, iron oxide, glass and saran microspheres, and air voids. Since the inclusions are uniformly distributed and the dimensions small compared to the ultrasonic wavelength (200 kHz), the elastic properties of this microinhomogeneous material may be characterized by the effective values of density, sound velocity, and modulus. It was found that effective values are strongly dependent on the type and concentration of inclusions. The results obtained are compared with current theories which predict the effective, or average, elastic properties of heterogeneous materials given the moduli (both longitudinal and shear) and density of the individual components.
Radiation from locally excited fluid loaded plates with two different types and spacing of periodic.supports
Authors: Berkman E. F. , Barger J. E. , Smith P. W.
Published: October 2005

A precise closed form analytic expression is developed for the radiation into a fluid from a point excited plate periodically supported by two different types of translational impedances with differing periodicities. This technique fully includes the effects of fluid loading and all mutual interactions between supports. Characteristics of the radiation field are examined by example and some physical interpretation of significant features are offered.
Scattering of ultrasound pulses in a suspension of particles
Authors: Sigelmann Rubens A. , Ishimaru Akira
Published: October 2005

This paper presents an experimental study of the propagation and scattering characteristics of ultrasound pulses in a suspension of particles, and comparisons with recent theoretical study on pulse diffusion [A. Ishimaru, J. Opt. Soc. Am. 68, 1045 (1978)]. Ultrasound offers some advantages over optical experiments because of its low velocity of propagation. Experiments are performed using bursts of 5-MHz pulses of 10-μs duration. The sample chamber is 5 ∼ 10 cm long and contains polystyrene particles of 0.6-μm diameter suspended in a self-buoyant solution of sugar and detergent. The transmitted pulse consists of coherent and incoherent waves. The coherent wave has a pulse shape identical to the incident pulse and it diminishes as the density is increased. The incoherent pulse is spread out in time and increases with the increase of particle density. The experimental data are consistent with the theoretical predictions.
Use of step response in inverse scattering
Authors: Resnick J. R.
Published: October 2005

Inverse scattering experiments can be used to infer the spatial dependence of the characteristic impedance of a transmission line, the density of layers in the earth's surface, or the cross-sectional area function of an acoustic tube. In past formulations it was necessary to measure the impulse response of the unknown structure. Such measurements can be difficult because of the difficulty of generating a good approximation to a delta function. In this paper, a method for inferring the unknown characteristic impedance from the step response is described. In some situations a step is easier to approximate than an impulse; in any case, the present procedure results in a decreased sensitivity of the resulting characteristic impedance to high frequency noise in the data. The method involves the solution of a nonlinear initial value problem.
Novel identification algorithm for adaptive FIR filters
Authors: Horna Otakar A.
Published: October 2005

Adaptive finite impulse response filters (AFIR) used to control echo in telephone lines and public address systems must have many hundred coefficients and process a highly correlated speech signal. Present AFIR theories based on the assumption that the reference signal is uncorrelated over time disagree with experimental results. Since the identification problem can always be reduced to a solution of a system of linear equations, Svoboda's algorithm for matrix inversion and postulates of matrix algebra can be used to derive conditions of solvability and convergence of these adaptive filters. Decorrelation of reference signal by two pseudorandom dither signals which select samples larger than rms value for computation of cross correlation is discussed. This method leads to a simple sign correlation algorithm. Adaptation speed is increased by updating the coefficient by multiplication by a constant 1 ± Δ the stability of the correction loop is improved by error signal averaging. Pseudologarithmic encoding of the stored samples reduces the memory size and simplifies the multiplication which is performed as the addition of binary logarithms. A piecewise linear approximation for binary logarithm is described. The above methods are used to build echo cancellers with 250 to 500 coefficients. They are in service in thousands of telephone circuits via communications satellites and in teleconference rooms.
An 800 bps speech compression system based on vector quantization
Authors: Wong David Y. , Juang Fred B. , Gray A. H.
Published: October 2005

Recent developments in vector quantization as applied to speech compression have allowed significant reductions in the bit rate of LPC vocoders. A 2400 bps LPC vocoder is being modified to operate at 800 bps while retaining acceptable intelligibility and naturalness in quality. The design of such a speech compression system is discussed and a demonstration tape played.
Critical periods of susceptibility to acoustic trauma in animals
Authors: Saunders James C.
Published: October 2005

In recent years the possibility that a maturing cochlea passes through a period of time in which it is unusually susceptible to acoustic trauma from noise exposure has been studied in a number of species. The conclusion from several sources suggests that the critical period for susceptibility to acoustic trauma is associated with developmental events within the cochlea. The data that support this conclusion will be reviewed. Evidence will also be presented to show the long-term maturation of middle-ear admittance in certain species. This phenomenon indicates that cochlear input may continue to develop over an extended period, and the implications of this for susceptibility to acoustic trauma in young ears will be considered. [Work supported by the Deafness Research Foundation.]
Aircraft noise and the health and behavior of children
Authors: Cohen Sheldon , Krantz David , Evans Gary , Stokols Daniel
Published: October 2005

The subjects were children with normal hearing attending the four noisiest elementary schools under a busy urban air corridor (LAX) and children attending three similar (matched on social class and race) quiet schools. Children were tested on the same measures twice with a one year interval between sessions. Cross-sectional data from the first session indicated that noisy school children had higher blood pressures than quiet school children. Noisy school children were also more likely to fail on a cognitive task and more likely to give up before the time to complete the task had elapsed. Longitudinal data were used to determine whether children adapt to the aircraft noise over the one-year period and to assess the effectiveness of noise abatement interventions introduced in a number of noise impacted classrooms. Additional cross-sectional data from the first session provided further information on the utility of noise abatement. There was little evidence for adaptation to noise over the one-year period. Abatement had small ameliorative effects on cognitive performance, children's ability to hear their teachers and school achievement. [Work supported by NSF and NIEHS.]
Engine fan noise in rear-engined vehicles
Authors: Staiano Michael A.
Published: October 2005

The engine cooling fan can be a significant source of noise in highway vehicles. For the majority of highway vehicles, the radiator and, consequently, engine cooling fan is mounted in the front portion of the vehicle where substantial benefit is obtained from the aerodynamic ram air effect when the vehicle is in motion—minimizing fan requirements. However, in transit and intercity buses the radiator is mounted along the side of the bus where no aerodynamic benefit is obtained; therefore, the engine fan operation is required for essentially all cooling system heat rejection. Measurements of fan usage were made on a transit coach while operated over a specified operating cycle. The cycle included a low-speed, Central Business District (CBD) phase as well as a high-speed, commuter phase. The measured fan usage for an approximately 30°F ambient temperature was approximately 13%. Fan usage requirements were estimated for other temperatures: approximately 11% at 0°F ranging to approximately 20% at 90°F. Engine operating cycle, i.e., loading conditions, also has a strong effect upon an engine heat rejection requirements. For the low speed (CBD) portion of the operating cycle, fan usage at 30°F was estimated to be 11%. For high speed operation (commuter), fan usage was estimated to be 22%. To determine the significance of fan usage to bus noise exposure levels, the fan usage such that the fan noise contributed greater than or equal to 1 dB to the operating cycle equivalent sound level, Leq, was estimated. This usage is a function of the fan sound level relative to the sound levels of all other bus noise sources. For two vehicles for which the fan sound levels were approximately 2.5 and 8 dB below the other bus noise sources, the fan usage becomes significant at 20% and 60%, respectively, based on the specified operating cycle.
Oral kinesthesia and the sensory-motor control of the tongue and jaw movements
Authors: Chuang C. K. , Abbs J.
Published: October 2005

Despite a great deal of research, the possible role of tactile kinesthetic sensory feedback in orofacial motor control is relatively undefined. The present experiment was an attempt to obtain some basic information concerning the kinesthetic resolution of tongue and jaw in positioning control. A self-regulatory discrete movement task, with and without visual feedback of the movement was employed. Initial findings of interest were kinesthetic sensibility differences in oral kinesthesia. preliminary data indicate that the jaw is superior in its resolution to the tongue, with kinesthetic JNDs of 1.2 and 3.0 mm, respectively. Further, the kinesthetic JND for depression (opening) was smaller than that for elevation (closing). Implications for jaw and tongue motor control for speech will be discussed. [Work supported by NS 13274.]
Tongue activity in compensatory speech: The use of articulatory models to interpret acoustical data
Authors: Hamlet S. , Reeves E.
Published: October 2005

The question addressed was whether, in compensatory speech, the vowel following a consonant articulated with an advanced or retracted tongue placement, would also show evidence of an advanced or retracted tongue posture. Palotographic data were used to determine tongue contact region for consonants. An articulatory model of tongue configuration [Harshman, Ladefoged, and Goldstein, J. Acoust. Soc. Am. 62, 693 (1977)] was used to interpret vowel formant frequency data for vowels. Additionally, vowel formant frequencies were adjusted to account for the effects of known compensatory jaw position. With jaw position corrections included the results were that vowels following a retracted or advanced articulation of sibilant and alveolar stop consonants, showed a similar retracted or advanced set of the tongue. This was not the case for vowels following /l/. Without adjustments for jaw positon the model predictions did not indicate a similarity in tongue set for vowels and consonants for any of the CV syllable types. [Work supported by NIH Grant DE-03631.]
Adaptive focusing: A spatial distortion-adaptive receiver
Authors: Claus A. J. , Labianca F. M.
Published: October 2005

Adaptive focusing is an array-processing scheme in which the receiver is designed for adaptive detection of localized sources under conditions where the signal field distribution across the array aperture is distorted from a plane-wave distribution, but is unknown a priori. The mechanisms responsible for the distortion, whether simple multipath or more complex propagation conditions, do not play important roles in the scheme. Rather, the emphasis is on estimation of the complex sensor responses using frequency domain processing and subsequent use of the resulting response vector to steer the array and thus maximize its output power for the signal sector of interest. The procedure exploits the spatial structure of the source field as it manifests itself in the eigenstructure of the sample covariance matrix. Whatever the physical mechanism causing the signal field distortion, the eigenstructure is generally such that estimation can be carried out in a unitary space of dimension significantly smaller than the number of sensors in the array. Clearly, temporal stability of the field distribution and signal-to-noise ratio are important parameters. Their influence on the detector has been studied and numerical results are presented. Monte Carlo simulation has shown that for threshold signals and under conditions for which a conventional beamformer is degraded by as much as 5 dB, adaptive focusing can perform within a fraction of 1 dB of an ideal beamformer for which the signal field was known a priori. [This work has been supported by the Naval Electronics Systems Command, Code ELEX-320.]
Acoustic signal flutter reduction using digital time base correction
Authors: Robinson D. C.
Published: October 2005

The flutter sidebands induced by magnetic tape recorders can degrade the resolution of recorded acoustic signals to an unacceptable level or obscure low level spectral details. These flutter effects are effectively suppressed using newly developed digital time base correctors. These all electronic, stand-alone instruments reduce the signal time base error from high performance laboratory recorders ten-fold. Since the corrected signal time base error is independent of recorder performance, greater relative improvement is obtained from portable or severe environment recorders. Spectral plots of simulated Anti-Submarine Warfare acoustic hydrophone data show a 50-dB reduction of flutter sidebands and suppression of the baseband flutter spectrum to below 80 dB down from peak signal. Comparing other flutter correction techniques—Tape Speed Servo Control typically suppresses flutter sidebands 20 dB; and Subtractive Flutter Compensation only suppresses the base band flutter spectrum but has no effect on flutter sidebands. Digital time base correctors interface with any standard instrumentation recorder, providing a capability to recover recorded acoustic data with minimal loss of resolution or low level spectral detail.
A binary detection model for at-sea sonar prediction
Authors: Franklin J. E. , Urick R. J.
Published: October 2005

The output of a sonar system is influenced to a large measure by the presence of fluctuating signals and noise. Because of these fluctuations, which frequently are greater than 30 dB over a period of 30 min, the prediction of the sonar output is a difficult task. This paper describes a new approach to the process of predicting whether or not there will be a detection at some time in the future. The output of a sonar is commonly clipped and thresholded to produce a binary-valued time series. This time series may be assumed to have a value of plus one, corresponding to a detection, or a value of negative one, corresponding to no detection. In this paper, a model of such a binary time series is developed from existing time series model theory in order to predict future values of the series. The binary prediction technique developed is applied to the prediction of the beam outputs of towed line-array sonars, as well as to the outputs of sonobuoys. Predictions based on the binary model give good comparison with the data, with a predictive accuracy of as much as 93% for shorter forecast lead times. Various other statistical properties of the time series are addressed in this paper.
A study of cymbal vibrations
Authors: Fletcher Harvey , Bassett I. G.
Published: October 2005

The vibration patterns of the cymbal were studied by driving the plate at edge with a sinusoidal signal. Chladni patterns were formed for sixty of the strongest modes of vibration. Typical patterns will be shown and discussed. Analyses were made of the sound from a single cymbal struck with a mallet. The vibration is very complex with more than 600 identifiable frequencies. Analysis was done passing the recorded sound through a 3-Hz bandwidth filter to isolate single frequency components. Information on decay rates was obtained using a 10-Hz bandwidth filter.
Findings from community surveys on the noise level/number of event trading relationship
Authors: Fields James M.
Published: October 2005

The value of different noise indices' characteristics can be better compared with regression rather than with correlation analyses. For these community noise indices, most of the debate has centered on the way in which three characteristics of noise events should be combined: peak noise level, number of events, and duration of events. Four types of indices have been proposed to combine these variables: energy hypotheses, simplified energy hypotheses, modified energy hypotheses, and interaction effect hypotheses. By breaking down the various indices into their component variables and considering each variable separately in regression analyses, the component parts of the theories underlying each of the indices can be directly examined. Three data sets (Tracor aircraft study, 1967 Heathrow study, and British Railway study) have been reanalyzed using this approach. Results from other studies are also reviewed. It is clear that knowledge about alternative noise indices would be enhanced in future studies if (1) component parts of the indices are separately analyzed, (2) a wide range of types of indices are compared in each research project, (3) noise level and number are not highly correlated in the sample, (4) the number of events is not confounded with other area-level variables in the sample, and (5) problems in counting numbers of events are addressed.
The saga of the plate-fluid interaction. II
Authors: Pierucci Mauro
Published: October 2005

Over the last two years, the author [J. Acoust. Soc. Am. 65, 1190–1197 (1979)] and other researchers have reanalyzed the plate-fluid interaction problem from different perspectives. In this paper the eigensolutions to the fluid-loaded thick plate equation are presented as a function of modulus of elasticity fluid loading and structural damping. The thick plate equation allows for the inclusion of shear deformation and rotary inertia effects on the vibrational response of the plate. Solutions for loci of the different modes as a function of frequency are presented in the fluid wavenumber plane. It is shown that under certain conditions the roots of the system cross from one Riemann sheet to the other thus changing the basic characteristics of the plate response and also of the radiated acoustic field. Internal structural damping is also shown to have the same effect upon the behavior of the root loci. Some of the phenomena discussed are a result of the rotary inertia terms in the plate equations and, therefore, cannot be explained by the use of the simpler thin plate analysis.