bluuebunny/crossref_metadata_2025 huggingface dataset:
Digital Equalizer and Deequalizer for Speech
Authors: Flanagan J. L. , Meinhart D. I. S. , Cummiskey P.
Published: November 2005

In the analysis and processing of speech, it is sometimes desirable to preemphasize the signal spectrum so that formant maxima are brought to nearly the same amplitude. A simple lumped-constant network is described for accomplishing this. A deemphasis network—the inverse of the former—is also described for recovering the original signal. The transfer functions for both networks exhibit four real-axis poles and four real-axis zeros. Sampled-data equivalents of both networks are derived, and the difference equations are programmed for the digital computer. Because the transfer functions have significant response at high-frequencies, the bilinear z transform is used to derive the difference equations. Errors arising from spectral folding about the sampling frequency are thereby avoided. Sampled and quantized speech signals are digitally processed by the program. The computer results are compared to circuit results obtained in the laboratory.
Speech Energy Rate of Change as a Function of Its Spectral Location
Authors: Focht Louis R.
Published: November 2005

An investigation of the first derivative of instantaneous speech power at any point in the spectrum was made by first assuming that the total energy variance is produced by two components: the amplitude modulation of the excitation wave and the movement of the formants. It was found that the effect of the amplitude-modulation component is to produce a uniform first derivative of power over the entire speech spectrum. The maximum rate of change produced by this component is 12 the fundamental pitch of the speaker. The change produced by the formant-movement component, however, does not exhibit a uniform rate of power change over the speech spectrum. Rather, it was found to fall off at the high and low end of the spectrum by more than 3 to 1 and attained a maximum rate of change, at 1000 cps, which was less than 13 that of the amplitude-modulation component. These studies were performed by using test sentences obtained from 5 male and 5 female speakers. No significant difference was found between male and female. [Work supported in part by the U. S. Air Force under contract No. AF19(628)-586.]
Formant Tracking by Majority Weighting of Period Measurements
Authors: Coulter D. C. , Campanella S. J.
Published: November 2005

A formant-tracking method based on the measure of majority period is discussed. This tracker employs as input data the instantaneous period measures of formants that have been selected by appropriate formant-range filters. These periods are subjected to an electronic circuit that, by a unique feedback arrangement, suppresses periods that deviate beyond a fixed threshold distance from the mean period. The resulting circuit output very nearly tracks the majority period of the set of periods that originally comprised the input data. The method also incorporates a means of weighting the majority period formant measure toward the median of the formant range. By this means, the tendency to be captured by adjacent formants is significantly reduced. The paper describes the method of implementation and the application of the method to formant tracking in the second-formant range. [Research supported in part by U. S. Army Electronics Research and Development Laboratory.]
Application of Delta Modulation to the Channel Vocoder
Authors: Teacher C. F. , Mutschler C.
Published: November 2005

The channel vocoder is steadily gaining acceptance as a practical and efficient digital voice-bandwidth-compression system. The vocoder creates a more compact bit stream by removing much of the redundant information contained in the speech waveform. However, it has been observed that individual channel signals are not completely independent of one another but are somewhat correlated. Similar correlations occur in the time domain and have been measured in both the spectral channels and the pitch information. This paper describes experiments in a simulated delta-modulation system designed to remove some of the redundancies in the waveforms. Detal-modulation oscillation effects are discussed, together with techniques to reduce their perceptibility. Experimental data are presented.
Waves of Finite Amplitude
Authors: Naugolnykh K.
Published: November 2005

The propagation of the finite-amplitude waves is considered in this paper, mainly with the help of the method based on the introduction of the “accompanying” system of coordinates. The distortion of the initially harmonic wave and its attenuation is described and some remarks on nonlinear effects in high-intensity ultrasonic focusing systems are given. The propagation of a nonperiodical compressional wave that is radiated by an expanding sphere is considered also.
Sound Generation by Inhomogenities Convected by a Steady Space-Varying Flow, or “Scattering” by Subsonic Waves
Authors: Powell Alan
Published: November 2005

Acoustic energy in ostensibly steady-flow systems such as rocket nozzles and water systems is generated by the convection of fluid inhomogemities—in composition, entropy or vorticity—through a spacewise varying flow, e.g., through a duct or past some curved surface. One-dimensional analysis is made by (a) an interaction method similar to that in J. Acoust. Soc. Am. 31, 1527 (1959), (b) the inhomogeneous convective wave equation, and (c) physical arguments hinging on differential fluid compression, momentum, and vorticity movement. The linear result for entropy fluctuations in a gas, for example, is that (acoustic-perturbation velocity)/(mean velocity)=−(fractional change in sound speed due to entropy)×(fractional mean pressure change) M/(1±M), the upper sign being for forwards-facing waves, M being the mean Mach number. Such linear results may be extended for finite steady-flow variations, including frequency effects, by the technique of J. Acoust. Soc. Am. 32, 1640 (1960). Method (a) is usable for large disturbances, while (b) and (c) are for one-, two-, or three-dimensional flows. The supersonic case, closely related to regular acoustic scattering, suggests an interesting parallel for “scattering” of subsonically propagating (“inhomogeneous”) waves. [Partial support from the U. S. Office of Naval Research.]
Airblasts Generated by Underwater Explosions
Authors: Dyer Ira , Malme Charles I. , Carbonell Jaime R.
Published: November 2005

The pressure-time history of airblasts produced by deep underwater explosions is characterized by a fast-rising peak (P1), a broader second peak (P2), and a subsequent rarefaction phase (P3). P1 is traditionally associated with the least-time propagation path. P2 and subsequent events are attributed to propagation through air from the surface zero region. While linear-continuum theory of airblast generation seemed to predict P1 with moderate success, its inadequacy in dealing with subsequent events signalled an inapt description of the interface reaction. Several experiments were performed to study the pressure contributions of selected portions of the water surface to the total airblast wave. The results indicated that the air-pressure pulse radiated by a surface element after the passage of an underwater shock was an “N wave” having a short, high-amplitude, positive phase followed by a longer, low-amplitude rarefaction. A modified Towne and Arons technique was developed wherein both phases of the elemental air-pressure pulse were considered in calculating the airblast waveform from contributions of successive surface regions. The development of this method and the agreement of results with experimental data are discussed. [Research was supported by the U. S. Naval Ordnance Laboratory.]
Flexural Horns
Authors: Pyle Robert W.
Published: November 2005

Tapered solid elastic rods have previously been used as horns or velocity transformers for longitudinal and torsional vibrations. Such structures may also be employed as velocity transformers when vibrating in flexure. An approximate 1-dimensional wave equation describing the vibration of such “flexural horns” has been derived from thin-bar theory. The wave equation can easily be solved for flexural horns uniform in thickness and exponentially tapered in width, vibrating in the thickness direction. The predicted mode shapes agree well with experimental measurements, but the predicted resonance frequencies are noticeably higher than those measured, the discrepancy increasing with increasing frequency. Comparison with published solutions for the uniform bar indicates that this discrepancy is probably due to the neglect of shear strains and rotary inertia in the formulation of the wave equation. [Work supported in part by the U. S. Office of Naval Research.]
Application of Photoelasticity to Research on Effects of Ultrasonic Stress Waves on Metals
Authors: Frandsen W. H. , Langenecker B.
Published: November 2005

The photoelastic effect in plastics offers the possibility to study the influence of several parameters, such as geometry and environmental conditions, on stress-wave patterns in solid rods irradiated by ultrasound. Irradiation of prototypes is accomplished through intimate contact of one end with an ultrasonic transducer operating at 20 kc/sec with intensities up to 200 W/cm2. The dependence of the modes and amplitudes of stress waves on shape, constraints, and localized heating—such as found in tensile tests [F. Blaha and B. Langenecker Acta Met. 7, 93 (1959)], crystal growth from the melt [B. Langenecker and W. H. Frandsen, Phil. Mag. 7, 2079 (1962)], and zone refining [B. Langenecker et al., NAVWEPS Rept. 8482, NOTS TP 3447 (1964), U. S. Naval Ordnance Test Sta., China Lake, Calif.]—is presented. Potentials of these studies in which photoelectric prototypes are used in place of metals are discussed, including an examination of coupling between ultrasonic horns and prototypes and a photometric determination of stresses.
Taut-Wire Delay Lines
Authors: Ashley George H.
Published: November 2005

The audiofrequency delay line reported at the 63rd Meeting of the Acoustical Society has been improved and used to synthesize transfer functions with specified characteristics in the time and frequency domains. Time delays from 8 to 20 msec are obtained using a 0.4-mil-diam platinum-alloy wire with transverse wave velocities from 168 to 67 m/sec. Magnet boards with 64 and 256 magnets have been used for signal synthesis. The magnets can be magnetized with specified amplitudes (within 5%) and polarities with a push-button magnetizer in about 15 min. A linear FM chirp was set up with five 20-msec delay lines in series giving 75 msec differential delay between 800 and 1600 cps and approximately uniform amplitude response. Viscous damping in the liquid termination is obtained using liquid propane for long time delays and liquid pentane for short time delays. The delay lines cover a 10 to 1 frequency range, from about 200–2000 cps for a 20-msec delay line and 1500–15 000 cps for an 8-msec delay line. Each delay line has a Vernier adjustment permitting the time delay to be varied ±5%. The group delay phase errors are small and in good agreement with classical theory.
Scattering of Sound by Atmospheric Turbulence: Application to Remote Wind-Velocity Measurement
Authors: Bricout P. A. , Kelton G.
Published: November 2005

A narrow sonic beam emitted continuously at 11 kc/sec by a Levavasseur whistle and sent at 15° elevation over ground, undergoes minute scattering by air disturbances and precipitations. Sensitive microphones at the focus of 4 ft parabolic reflectors detect the sound scattered from the beam at distances from 70 to 100 ft. The received sound shows a frequency shift, which can be explained by successive Doppler effects between source and scatterers carried by the wind and between the latter and receiver. Theory shows and experience confirms that the observed frequency shift is proportional to the component of wind-velocity normal to the line joining the source and the receiver. Tracking oscillators synchronized on the received signal compensate for frequent amplitude changes and permit continuous frequency measurements, even in presence of brief fading. By using two receivers located North and East of the source, oscilloscopic display of wind-velocity vector and/or continuous records of N-S and E-W wind components have been obtained. Measurements agree with anemometer and wind-vane readings within ±1 mph and ±5°.
Investigation of Sound Propagation in Urban Areas
Authors: Wiener Francis M. , Malme Charles I. , Gogos Creighton M.
Published: November 2005

Outdoor civil-defense alerting and voice-warning systems for urban areas have been traditionally designed. using relatively few sources of sound high above the buildings. Results have generally not been satisfactory because of sound attenuation in the atmosphere and diffraction by buildings. As an alternative, a block-by-block coverage system using many directive sound sources placed in the streets has been investigated. Extensive acoustical and meteorological field tests carried out in city streets showed that sound-propagation conditions are generally favorable there. Typically, the mean wind and temperature gradients are small; consequently, no appreciable sound-refraction effects were observed over distances of a city block or two when sound was propagated from a source 10 20 ft above the pavement. Reverberation from the building walls was not detrimental to speech intelligibility when a directive sound source was used with its axis oriented along the street. However, the intelligibility of speech received in a side street some distance away from the intersection was poor owing to excessive sound attenuation and reverberation. [Work supported by the U. S. Office of Civil Defense.]
Noise Control and the New York City Code Project
Authors: Kodaras Michael J.
Published: November 2005

A new building code for the City of New York is in the preparation stage. When completed, it will be submitted to Charles E. Schaffner, Vice-President of Polytechnic Institute of Brooklyn and his staff. The noise-control requirements will apply to apartment dwellings and include provisions for minimum airborne-sound insulation between apartments, impact isolation of floor constructions, and requirements for airborne and structural isolation of mechanical equipment. A brief description is given of the preliminary noise-control submission for this new building code.
Physiological Parameters of Speech
Authors: Ladefoged Peter
Published: November 2005

This paper relates the two succeeding papers to a larger frame of research. As a hypothesis, it is suggested that speech may be specified in terms of the following physiological parameters: (1) pressure of the air in the trachea; (2) position of the vocal cords; (3) tension of the vocal cords; (4) degree of velo-pharyngeal stricture; (5, 6) coordinates of the center of the body of the tongue; (7, 8) coordinates of the tip of the tongue; (9, 10) protrusion and opening of the lips. Additional parameters are also required to account for the shape of the vocal tract in some sounds. As part of a research project, work is proceeding on the collection of data and the construction of speech synthesizers, which will allow the testing of this hypothesis concerning the description of speech. [Work supported by the Public Health Service, U. S. Department of Health, Education, and Welfare, under grant No. NB-04595.]
Articulatory Activity in Vowels
Authors: Lindblom Bjorn E. F.
Published: November 2005

Cinéradiographic data have been obtained that illustrate certain dynamic aspects of vowel articulation. The material analyzed consists of CV, VC, and CVC sequences, some of which were uttered at varying speeds. Special attention has been paid to the rate and timing of movements and to the extent to which individual articulatory components reach their hypothetical target positions within an utterance under various conditions. Instances of articulatory undershoot relative to an ideal target configuration can be observed and appear to be more pronounced as the rate of utterance is increased. The results are interpreted in relation to acoustic data on Swedish vowels previously reported [J. Acoust. Soc. Am. 35, 1773 (1963)]. [Research supported in part by the Wenner-Gren Foundation for Anthropological Research, Research Institute of the National Swedish Defence, Swedish Technical Research Council, Telefonaktiebolaget LM Ericsson, Swedish Foundation for Scientific Research and Industrial Development, U. S. Air Force under grant AF EOAR 63-55, U. S. Army under contract DA191-591-EUC-3080, National Institutes of Health, U. S. Department of Health, Education, and Welfare, under research grant NB-04003-01.]
Numerical Model for Coarticulation, Using a Computer-Simulated Vocal Tract
Authors: Öhman S. E. G.
Published: November 2005

Previous research based on measurements from x-ray motion pictures and sound spectrograms has indicated that for languages such as Swedish and English a vowel +stop+vowel utterance is not a sequence of three concatenated articulatory gestures but rather a stop-consonant gesture superimposed on the transition part of a diphthongal vowel motion. In the present paper, an attempt is made to develop a numerical model for these coarticulation phenomena. The model generates sequences of vocal-tract shapes representing the desired VCV utterances in terms of a small number of control parameters related to the articulatory activities of the tongue. The vocal-tract shapes and their associated acoustic outputs as calculated from the model are compared with natural VCV utterances. The relevance of the methods presented in a general synthesis-by-rule context are discussed. [Work supported in part by the U. S. Army Signal Corps, the U. S. Air Force Office of Scientific Research, and the U. S. Office of Naval Research; in part by the National Science Foundation (grant G-16526), the Nation Institutes of Health, U. S. Department of Health, Education, and Welfare (grants MH-04737-03, NB-04332-01, and NB-04003-01), and the National Aeronautics and Space Administration (grant NsG-496); and in part by the U. S. Air Force (ESD) under contract AF19(628)-3325 and under grant AF EOAR 63-55, and by the U. S. Army under contract DA-91-591-EUC-3080.]
On the Construction of a Dynamic Vocal-Tract Model
Authors: Dennis Jack B. , Whitman Edward C. , Tomlinson Raymond S.
Published: November 2005

A new technique for realizing a transmission-line (articulatory) analog of the human vocal tract is described. Essentially, the acoustic equations governing sound propagation in a cascade of short, circular cylinders are solved on a configuration of operational amplifiers, using the methods of analog computation to process the signal from source to output. The coefficients of the relevant equations are set by the use of digitally controlled attenuators in the signal paths, and hence the synthesis can be controlled in real time by a digital computer. Included is a description of the circuitry developed to date, with emphasis on the digitally controlled attenuators, and an analysis of stability and noise problems encountered in this approach. [Work supported in part by the U. S. Army Signal Corps, the U. S. Air Force Office of Scientific Research, and the U. S. Office of Naval Research; in part by the National Science Foundation (grant G-16526), the National Institutes of Health, U. S. Department of Health, Education, and Welfare (grants MH104737-03 and NB-04332-01), and the National Aeronautics and Space Administration (grant NsG-496); and in part by the U. S. Air Force (ESD) under contract AF19(628)3325.]
New Method of Deriving the Reflection Coefficient for a Fluid Layer
Authors: Harrison Mark
Published: November 2005

The problem of computing the reflection and transmission coefficients for a sound wave that is normally incident upon a uniform fluid layer whose constants differ from the rest of the medium is a familiar text-book illustrative example. In this paper, a new method for treating such problems is presented that in many respects is physically more insightful. The method is based upon the concept of partial waves whose phases are altered by the presence of the layer. While the amount of algebra used is about the same for this method of partial waves as for the standard boundary-condition method, it is shown that the method of this paper can be extended so as to be useful for more-complicated cases where the physical parameters of the layer vary continuously so that the boundary-condition method cannot be used.
Ultrasonics Relaxation in the Study of the Rotational Isomers of Iso-Propyl Formate
Authors: Subrahmanyam S. V. , Piercy J. E.
Published: November 2005

The ultrasonics absorption of dilute solutions of isopropyl formate in xylene and n-heptane has been measured at frequencies of 0.6, 1.8, 3.0, and 45 Mc/sec for a number of temperatures in the range 30° to 80°C, using acoustics streaming and pulse techniques. Application of relaxation formulas for a 2-state interconversion reaction to these measurements yields a relaxation frequency of 1.1 Mc/sec at 50°C, a difference in enthalpy between states of approximately 4.2 kcal/mole, and an Arrhenius activation energy and frequency factor for the conversion of the higher-energy state to the lower of approximately 6.2 kcal/mole and 1011 sec−1, respectively. A possible molecular mechanism is the interconversion of cis and trans isomers by internal rotation about the C–O bond. The activation energy is then a measure of the amount of double-bond character imparted to this bond by chemical resonance.
Sound Velocity in Stressed Crystals and Third-Order Elastic Coefficients
Authors: Brugger K. , Thurston R. N.
Published: November 2005

Third-order elastic coefficients can be determined from the velocity of small-amplitude sound waves in statically stressed media. For this purpose, exact expressions are derived for the sound velocity, for the natural velocity (natural unstressed length divided by the transit time), and for their stress derivatives, evaluated at zero stress, in terms of second- and third-order coefficients. Attention is given to the proper variation of propagation direction with static stress in order to maintain propagation normal to a given crystal face as in ultrasonic experiments, and to the proper identification of isothermal and isentropic coefficients. The most convenient form of the results employs the natural velocity, which is computed directly from experimental data with no need to correct the path length for the effect of stress. The formulas apply to arbitrary crystal symmetry and to arbitrary homogeneous stress systems depending on a single scalar variable. Special formulas for hydrostatic and uniaxial stress are given for several crystal classes and for isotropic materials.
Lateralization of Tones and Clicks
Authors: Hafter Ervin R. , Jeffress Lloyd A.
Published: November 2005

Several years ago, Whitworth and Jeffress examined Bannister's generally overlooked contention of 1927 that low-frequency tonal stimuli with dichotic intensity differences could be lateralized in two places. They reported trading ratios for two, simultaneously heard, locations; one fell in the respectable range often found, but the more elusive location had a trading ratio as small as 0.3 μsec/dB, a smallness of magnitude rarely reported. They contrasted these small trading ratios to the larger ones typically found for clicks and suggested that more than one peripheral mechanism might be responsible. Several papers have hypothesized that the trading ratios found with clicks might be due to the delay of N1 as formed at the basal end of the cochlea, and those for tone on neural activation at the hair cell. Neither account discusses question of when do tones become clicks. The present paper explores this question by extending the Whitworth and Jeffress “two-place lateralization” phenomenon to cover both clicks and tones of several durations and rise times.
Effect of Noise Crosscorrelation for a Narrow-Band Masking Noise on the Detection of a Tonal Signal
Authors: Langford Ted L. , Jeffress Lloyd A.
Published: November 2005

This is an extension of a study of the effect of the crosscorrelation for a masking noise upon the detection of a tonal signal reported in 1963 by Langford and Jeffress. In the previous study, a wide-band noise was used, while in the present study a narrow-band noise approximating the critical band at the signal frequency was employed as the masker. The crosscorrelation of the masker was varied by introducing a time delay into the channel to one ear. The signal was presented in-phase at the ears and reversed-in-phase at one ear. Data are presented as masking-level differences (MLD's) relative to the undelayed homophasic condition. The function relating MLD's to values of correlation is cyclic and becomes damped as the noise delay is increased. The MLD's for antiphasic conditions are larger, however, than those obtained for wideband noise. The results are discussed in terms of a model for binaural hearing.
Perceived Order of Tone Pulses
Authors: Peters Robert W.
Published: November 2005

Observers adjusted the frequency of a pulse that was in the middle of a series of three tone pulses until the middle pulse was heard to occur last. This perceived order, different from that of the actual temporal order, was achieved by either increasing or decreasing the frequency of the center pulse. The frequency of all three pulses was the same at the beginning of each testing trial. The amount of either frequency increase or decrease necessary to bring about the perceived change in order was examined in the frequency range from 200 to 5000 cps and for pulse durations and pulse intervals in the range from 10 to 80 msec. The results indicated that the frequency change necessary for the middle pulse to alter perceived order increased as the test frequency was increased. The obtained frequency values corresponded with those associated with critical band measures. [Research supported by Aeronautical Systems Division, Wright-Patterson Air Force Base, under contract AF 33(657)-10681.]
Measurement of Individual Stimuli in a Signal-Detection Task
Authors: Watson Charles S.
Published: November 2005

Listeners judged the presence or absence of a 1000-cps sinusoid in each of 4400 0.25-sec bursts of broad-band, thermal noise. The spectral level of the noise was 45 dB SPL; the value of E/N0 was 12.6. Half of the bursts included the signal throughtout their duration. Judgments were made on a 4-point rating scale. The bursts were recorded simultaneously on magnetic tape. Voltage peaks were later measured within a 100-cps band centered on the signal frequency for each of the bursts. Average stimuli, in terms of weighted sums of voltage peaks, are described for each of the points on the rating scale. Average ratings are presented for each decile along the stimulus continuum. Rating responses are found to be dependent upon the level of the stimulus whether signals are, in fact, present or not. Psychophysical methods that include corrections for random “guessing” are clearly inappropriate to this sensory task. [Research conducted at the Hearing and Communication Laboratory, Indiana University, Bloomington, Indiana, and was accomplished under contracts AF 19(604) and AF 19(628)-266 with the Operational Applications Laboratory.]
Detection of Markovian Sequences of Signals
Authors: Friedman Morton P. , Carterette Edward C.
Published: November 2005

This experiment investigated the effects of different stimulus contingencies on signal detection. Three observers were run in a 2-interval temporal forced-choice task. The signal was a 1000-cps gated sinusoid presented against a background of band-limited Gaussian noise. Feedback information was given after each response. Nine different probabilistic schedules of signal presentation were employed. The sequences of stimulus events were generated by a first-order Markov process. The schedules differed both in over-all probability and repetition probability of a signal in a particular interval. Some of the principal results were: (1) ROC plots of the over-all individual response proportions indicated that a single function fitted the data for each observer reasonably well. There was a suggestion, however, that detectability was higher for schedules involving extreme repetition probabilities. (2) For all schedules, there was a strong dependence of responses on the immediately preceding stimuli, the nature of the dependence being clearly related to the particular schedule. (3) The probability of a correct detection generally increased during a run of trials in which the signal recurred in the same interval. The probability of a correct detection on the first trial of a run in a given interval was independent of the length of the preceding run of signals in the other interval. [Work supported by the Public Health Service, U. S. Department of Health, Education, and Welfare, contract MH 07809, by the U. S. Office of Naval Research, contract Nonr 233(58), and by the National Aeronautics and Space Administration, contract NSG 237-62.]
Information and Complex-Signal Perception
Authors: Chaney Robert B.
Published: November 2005

Information processing with certain multidimensional auditory signals was investigated as a function of observers' previous experience in the identification of those signals. Physically similar signals representing speech sounds and sonar signals were presented for identification of 4 to 6 dimensions, including source, content, localization, and variations of duration and frequency. Two groups of listeners were selected, both with similar linguistic background, but one with extensive training in sonar-signal perception, while the other was essentially naive in this respect. These groups attempted to identify under pressure of time the dimensions of each test signal as it was presented simultaneously with an irrelevant signal. Information-transmission rates were determined for each dimension of each signal type (speech, sonar), and the results discussed in terms of a hypothesized perceptual hierarchy of response that depends not so much on the physical properties of the signal per se, but rather on the listener's familiarity or experience with them.
Acoustics and People
Authors: Burris-Meyer Harold
Published: November 2005

This paper postulates as a worthy, but often overlooked objective of acoustical research the discovery, definition and development of means to achieve an acoustical environment that shall be most conducive to man's welfare, his health, his enjoyment of the arts, his means of self-expression. The ways in which much acoustical research and the applications thereof to architectural and psychological problems deviate from or ignore this ideal are cited. Means to achieve it are proposed.
Fluctuating Acoustic Refraction in the Deep Water of the Caribbean Sea
Authors: Lord Norman W.
Published: November 2005

The velocity of sound in the Caribbean was measured with high sensitivity and data-sampling rate, using the automatic NBS type of velocimeter. At four latitudes between 16° N and 13° N, a meter moving at 2 knots at a depth of 800 m was read 4 times per second. A statistical analysis was made in terms of the deviation in sound velocity from a moving average over 10 m of path length, which eliminated the influence of depth variation. Over the four latitudes, rms deviations were between 0.05 and 0.08 msec−1. All of the normalized autocorrelation coefficients showed the same shape as a function of space interval. The first null, a measure of “patch size,” was generally around 1.2 m. North of Bonaire Island, the sound velocity was monitored at depths between 300 and 1200 m, with a stationarily suspended set of 3 velocimeters. They were sampled simultaneously, one every 9 sec, and a similar moving average technique was used in analysis. The best evidence available for the underwater current indicates that the averaging length varied from 10–20 m. The rms deviations were from 0.05 to 0.12 msec−1 for depths greater than 500 m. The spacings between the meters were 9, 12, and 21 m, and there was no discernible crosscorrelation of the sound-velocity deviations. By careful comparison with similar but differently observed results for deep Atlantic Ocean water, it is quite clear that the inhomogeneity of the Caribbean is generally smaller and finer grained. [Hudson Laboratories of Columbia University Informal Documentation No. 42. Work supported by the U. S. Office of Naval Research.]
Improvements in the Seismic Profiler
Authors: Caulfield David D. , Hoskins Hartley , Nowak Richard T.
Published: November 2005

Three improvements in the continuous seismic profiling system used by the Geophysics Department of the Woods Hole Oceanographic Institution are the use of (1) an electrical-spark sound source of 100 000 J maximum stored energy, which can produce a variety of acoustic pulses with peak pressures of up to 134 dB above 1 dyn/cm2, at a repetition period of 10 sec with a conversion efficiency (stored electrical energy to acoustic output energy) of 10%, (2) streamlined, neutrally buoyant, line-hydrophone arrays with bandpass from 20 to 1000 cps, and (3) a matched-filter detector that correlates the reflected signal, with the outgoing signal achieving as much as an 8-fold improvement in the signal-to-noise ratio. This system has been used at ship speeds up to 11 Kt in continental-shelf areas, with penetrations of up to 0.8 sec and at 5 Kt in deep-sea areas with penetrations of up to 1.3 sec. Each of these improvements is discussed and data taken with this system are compared with data taken with earlier systems.
Statistical Study of the Wind-Driven Surface of an Underwater Acoustic Model Tank
Authors: Tetreault D. E. , Hill R. F.
Published: November 2005

Underwater acoustic signals in general follow a complex paths. One of the important paths is a single bounce off the surface of the ocean. In order to carry on controlled experiments in a model tank, it is necessary to create a model sea state whose characteristics resemble those of the real ocean. It is also important that the statistical characteristics be known and stationary with respect to both time and position on the surface of the water. The model sea state is generated by the movement of air created by a bank of fans mounted at one end of the 12×4×4-ft model tank. The outputs of two instantaneous waveheight indicators are digitized and analyzed on a digital computer. Autocorrelation, crosscorrelation, probability density, and power spectral-density functions are obtained as a function of time and position of the indicators. These functions are compared to real ocean data presently available. [Work supported by the U. S. Office of Naval Research and the U. S. Navy Underwater Ordnance Station, Newport, R. I.]
Radiation Field of a Symmetrically Oscillating Two-Dimensional Cavity Flow
Authors: Leehey Patrick
Published: November 2005

A symmetrically oscillating two-dimensional cavity is produced in a compressible inviscid fluid by a suitable singularity of sinusoidally time-variable strength moving rectilinearly at velocity U. The restrictions M=U/C∞<1 and σ=(p∞−pc)/12ρ∞U2>0 are imposed, where pc is the vapor pressure in the cavity and the speed of sound c∞, the pressure p∞, and the density ρ∞ are those of the undisturbed fluid. The problem is linearized by the assumptions that the perturbation-velocity components are much smaller than U and that the cavity length l is fixed at its steady-state value. An expression for the unsteady velocity potential is formulated using an approximate Wiener-Hopf technique valid for large values of l. By use of an Abelian theorem extended in the finite part sense of Riesz, the solution in the Fourier transform plane is shown to be unique, provided the singularities representing the two ends of the cavity are of order <3/2.
Measurements of Pressures on a Rigid Pipe Wall due to Turbulent Air Flow
Authors: DeMetz Fred C. , Jorgensen Donald W. , Devin Charles
Published: November 2005

The power-spectral densities of the pressure fluctuations in a turbulent air flow have been measured on a rigid pipe wall by a small pressure transducer. The turbulence was fully developed throughout the cross section of the pipe. Measurements were possible over a very wide range of Reynolds numbers, based on pipe diameter, from 20 000 to 460 000. The data indicate that there exists a dependence of spectral densities on the Reynolds number. Spectral densities were measured for a Strouhal number fR/u as low as 0.02, where f is the frequency, R is the radius of the pipe, and u is the center-line velocity. These results are of interest since not all investigators are in agreement on data obtained for low values of Strouhal number.
Some Theoretical Aspects of Noise Generation in Shipboard Water Systems
Authors: Peter A. C. , Kamo R.
Published: November 2005

Proudman's derivation for noise generation by isotropic turbulence is extended to the case of nonisotropic turbulent flows, in accordance with his original suggestions as presented in his paper. The rate at which energy is being supplied to the turbulent regions from an external source is derived using the energy equation and the equation of state for water. Theoretical approaches are derived for the case of noise generation in a pipe, constriction and water discharge into a stagnant reservoir. These considerations indicate that the acoustic intensities for these cases vary as U6.75, U5and U8, respectively.
Mach Wave Radiation from a Highly Sheared Supersonic Turbulent Flow
Authors: Williams J. E. Ffowcs , Maidanik Gideon
Published: November 2005

The turbulent sources responsible for Mach-wave emission are shown to be particularly simple whenever the mean velocity gradient is large. Their strengths become directly proportional to the mean shear that amplifies a fluctuating term linearly dependent on the turbulence velocity. Such waves have an added directionality that is similar to that occurring at subsonic speeds in tho presence of large velocity gradients. In the Mach-wave case, since direction and Mach number are related, their directional dependence is best described as an additional Mach-number effect. The radiation intensity I is then shown to be proportional to the mean shear τ and Mach number M in the following way: I∼ρc(l4/r2)τ2[(M2−1)/M3], where ρc is the characteristic impedance, l a typical turbulence scale, and r the distance traveled by the sound. This result is compared with some experimental observations of the sound radiated from turbulent boundary layers. [Research supported in part by the National Aeronautics and Space Administration.]
Turbulent Boundary-Layer Pressure Fluctuations Over Two-Dimensional and Narrow Delta Wings
Authors: Richards E. J.
Published: November 2005

The paper summarizes work now going on at the Institute of Sound and Vibration Research on turbulent boundary-layer pressure fluctuations on 2-dimensional surfaces and relates these results to those of other investigators. The questions of Mach number, vibration, and low-frequency content are discussed. Further investigations on 3-dimensional surfaces such as narrow delta wings show that, under vortex flow conditions, the pressure fluctuations can be 3 times the magnitudes obtained above, and under conditions of vortex breakdown can grow to 10 times the 2-dimensional values. Spatial correlation curves are shown and discussed. The possible mechanisms for this deviation from 2-dimensional excitation values are discussed in the light of these correlation curves and in the light of other work carried out in the United Kingdom.
Importance of Superimposed Acoustic, Static, and Dynamic Loadings and Their Application to Aerospace Structural Testing
Authors: Wilhem D. P.
Published: November 2005

The effects of interactions between acoustic, static, and dynamic loadings during design and analysis of structures have received relatively little attention. Now, the importance of combined-loads reliability testing has been documented by an aerospace survey. Numerous premature acoustic-fatigue failures were uncovered—indicating the necessity for time-mission-history simulation during testing to ensure realistic environmental loading. In this study, the importance of combined acoustic, static, and dynamic loadings is discussed in terms of (1) general principles that must be considered, and (2) testing arrangements that are applicable to difficult and costly vehicle-reliability problems. Methods are presented for selected combined-loading situations, which are graphically illustrated to show appropriate means of load application when test articles are simultaneously subjected to high-energy acoustic environments. Several new approaches are presented to the load-superposition challenge requiring accurate simulation and noninterference with structural response during sonic excitation. Typical of the proposed combined-load arrangements is that of an engine-intake airduct that is subjected during service life to considerable fatigue-induced damage contributed by high-frequency compressor whine, static differential pressure, and dynamic unbalance. An unconventional solution to this problem is suggested whereby the fatigue-producing parameters are simultaneously introduced without utilizing an operating engine.
Consistency of Identification of Consonants Heard in Noise
Authors: Pollack Irwin
Published: November 2005

Confusion matrices, representing stimulus-response combinations for sets of four consonants, were tested for consistency by three separate methods of analysis. Three sets of four consonants in syllabic form and a wide range of speech-to-noise ratios provided a wide range of confusability scores. Two conditions of presentation were examined: a given syllable and its noise background were recorded and played back over the course of 12 replications of a series of test lists; or, 12 separate readings of each syllable against independent noise backgrounds were recorded within a single test list. Greater consistency of response is obtained for the recordings of both the syllable and its noise background than for recordings of syllable presented against independent noise backgrounds. The results suggest that the instant-by-instant relationships between speech and its noise background may be a strong determinant of the identification of speech in noise.
Perceptual Reorganization of Repeated Speech Sounds
Authors: Warren Richard M. , Warren Roslyn P.
Published: November 2005

Illusory changes called “verbal transformations” (VT's) may occur with continued listening to reiterations of a single word. It has been found that: (1) VT's are absent at the age of 5, and occur for virtually all children 8 years old. Susceptibility to VT's is maintained through childhood, adolescence, and young adulthood; it seems to decrease somewhat by the age of 35, and it is generally absent for those over 60. (2) The appearance of VT's in children at the age of 6 or 7 approximates an all-or-none phenomenon—that is, their rate of illusory changes is about the same as that of older children and young adults. (3) The phonetic differences between successive perceptual forms is greatest for young children and decreases regularly with age, (4) The units of perceptual organization seem to be real words for the aged (they seldom report nonsense words), phoneme clusters for young adults (they frequently report nonsense words, but never groupings of speech sounds not found in English), and individual phonemes for children (they report “words” with phoneme clusters not found in English—e.g., “shlime”). These observations with repeated words suggest mechanisms underlying comprehension of normal speech discourse.
Emotional Effects of Fundamental-Frequency Transformations
Authors: Lieberman Philip , Michaels Sheldon B. , Soron Henry I.
Published: November 2005

Fundamental frequency was derived from the utterances of speakers of American English. Each read a total of 40 simple sentences. The words of these sentences express fear, anger, joy, or “neutrality.” Each sentence was read 4 times by the speakers, who attempted to convey one of these emotions by their manner of speaking, even though the lexical content and the emotion might not correspond. Test stimuli were synthesized by exciting a fixed POVO with several sets of fundamental frequency contours: (1) the contours derived directly from the original signal, and with the mean fundamental frequency raised, normal, or lowered; (2) the original contours with the frequency range compressed, and with the mean fundamental frequency raised, normal, or lowered; (3) the original contours with the frequency range increased, and with the mean fundamental frequency raised, normal, or lowered. These stimuli were first presented to subjects in forced-choice categorization tests in which subjects had to decide whether the POVO's output conveyed fear, anger, joy, or “neutrality.” Listening tests in the free-choice mode were also performed. The effect of these transformations on the emotions conveyed are reported and interpreted in the light of a general theory regarding the function of the prosodic speech features in language.
On “Calibrating” the Linguists' Perception of “Phonemic” Pitch and Stress Levels
Authors: Lieberman Philip
Published: November 2005

A system developed by Trager and Smith for the transcription of pitch and stress is in wide use by linguists. Four pitch levels, four stress levels, and three “terminal contours” are used to differentiate special prosodic “morphemes,” which are supposed to carry specific meanings that are independent of the sentences' words. This experiment shows that these “phonemic” elements may have no acoustic correlates; the linguist infers their presence from the words of the sentence, the schema of the Trager-Smith system, and his intuitive knowledge of the language's structure. The words convey the sentence's meaning to the linguist who then “fills in” the pitch and stress levels appropriate to the prosodic “morphemes” that have that meaning. A set of sentences was transcribed by two skilled linguists. The sentences were electronically processed so that the words were removed, leaving only the contours and stresses. (A POVO was excited with the pitch and amplitude information extracted from the original sentences.) The transcriptions of the POVO output differed markedly from the transcriptions of the complete sentences, except for the primary stresses and final pitch contours. Control procedures confirmed that the linguists were transcribing the actual acoustic signal for the POVO output.
Recognition of Lexical Tone in Mandarin Chinese by Sampling of Fundamental Frequency
Authors: Brotzman Robert Lee
Published: November 2005

A list of isolated syllables, connected nonsense syllables, and meaningful phrases was read by two speakers of Mandarin Chinese. Recordings of this speech were then analyzed, using a modified “vocoder” pitch extractor whose output was connected to a graphical recording system. The graphical record of frequency was then sampled at 40-msec intervals during voicing. Certain parameters of the discrete-pitch curve were then extracted by a digital computer, and these were examined to determine their reliability in recognizing which tone was spoken. As a remit of this study, the parameters for recognizing the tone of an isolated syllable by fundamental frequency were specified and a tone-recognition procedure for connected, but segmented, speech was produced. [Work supported by the U. S. Office of Naval Research grant No. NONR-495(27).]