bluuebunny/crossref_metadata_2025 huggingface dataset:
Additional Theoretical Implications of Binaural Beats
Authors: Tobias Jerry V.
Published: September 2005

Historically, the phenomenon of binaural beats has been considered to be a strong indication of binaural beats has been considered to be a strong information. Usually, one listens to the beats with bilaterally matched sound-pressure levels (zero interaural intensity difference). However, in investigating the limits of dichotic intensity which permit binaural beats, it was noted in the present study that subjects respond to the presence of beats whenever the tones to both ears are above threshold. The frequency range investigated was 100 to 2000 cps. As other authors have previously reported, the best performance occurred in the 500- to 600-cps range. It is obvious (after the fact) on the basis of any of several of the popular schemes used for representing binaural interaction that the binaural beat should follow a physiological rather than a physical logic. The case for separate timing channels in the auditory nervous system is thus further strengthened. The phenomenology of the “unbalanced beat” and implications for pitch theory as well as for binaural interaction theory are discussed.
Binaural-Click Lateralizations with a Three-Click Paradigm
Authors: Guttman Newman
Published: September 2005

The plan of this experiment was to fix one click in each ear to produce a centered image, to add a roving click S to one ear, and to observe the movements and quality changes of the auditory images as the distance between the roving and fixed clicks varied. The stimuli were all-pass, 70-μsec clicks presented once per second at 36-db SL in dynamic earphones. The results show, among other things, that the image produced by the fixed pair is displaced from center by S located within about ±25 msec of the pair. This image disappears when S leads by less than 3–4 msec. In the S ear, the image corresponding to S departs from the ear when S leads the pair by about 20 msec and returns after S lags by more than 5–8 msec. These effects are produced by a combination of monaural and binaural interactions difficult to disentangle.
Backward and Forward Masking of Probe Tones of Different Frequencies
Authors: Elliot Lois L.
Published: September 2005

Both monotic (masking and probe presented to same ear) and dichotic (masking and probe presented to opposite ears) conditions were used to investigate backward and forward masking. White noise in a 50-msec burst at 90-db SPL served as masking. Probe tones at 500, 1000, and 4000 cps with 7-msec duration preceeded or followed the masking with interspersed silent intervals ranging from 0 to 100 msec. Results showed that backward monotic masking occurred for intervals as long as 50 msec for 500 and 1000 cps and 20 msec for 4000 cps. In the dichotic condition, backward masking at 500 and 1000 cps occurred for intervals as long as 10 to 15 msec, while for 4000 cps it was observed for about 5 msec. At very brief masking intervals for the backward monotic condition, 4000 showed greater masking; however, this did not occur in the forward monotic condition nor in either of the dichotic conditions. Implications of these results are considered.
Combating Echo in Speech Circuits with Long Delay
Authors: Gardner Mark B. , Nelson John R.
Published: September 2005

In speech communication systems, echo arises from impedance discontinuities at the various circuit junctions. In telephonic communication, echo is universally present to a greater or lesser extent. However, it usually goes unnoticed on short connections where the round-trip signal transit time of a few milliseconds or less is too short to give an audible separation of direct and reflected components. Echo suppressors have have long served to alleviate the problems of echo return on circuits with moderate delays. One of the design problems is to remove echo without interfering with the two-way flow of speech during periods of double talking. In view of recent interest in satellite communication systems, where delay times of the order of hundreds of milliseconds may be involved, a review of echo-suppressor performance under more severe operating conditions has been undertaken. This paper discusses the special problems involved in suppressing echo on circuits with long delay. It describes an experimental solid-state device for detecting and combating echo in such circuits. In particular, the questions of differential break-in and voice-controlled loss in the return path are considered. A demonstration is given of the operation of the experimental device under different conditions of circuit echo.
Preference Judgments of Transmission Quality
Authors: McDermott Barbara J.
Published: September 2005

Listener's choices were elicited for each of the possible ordered pairs of a set of 22 different circuits to determine whether they reflected an orderly preference structure. Thirteen of the circuits were specifiable in terms of speech level, noise level, and bandpass-filter characteristics, while the others represented more-complex distortions. A comparison consisted of two prerecorded sentences transmitted through each of two circuits. Individual and group rank orders and individual preference consistency were investigated. The subjects' rank orders determined by the total number of times each condition was preferred were very similar, particularly for the highest and lowest rankings. The circuits in the midrange showed larger between subject variability in order, and it was with regard to these degradations that the subjects showed considerable inconsistency in their preferences. Inconsistency with regard to particular pairs of circuits was manifested both by reversals upon repetition and by choices contrary to over-all rankings. Some of this inconsistency can be attributed to an order bias. The significance of the individual differences and the scalability of the group results are discussed.
Simplified Nonsense-Syllable Tests for Analytic Evaluation of Speech Transmission Systems
Authors: Stevens Kenneth N.
Published: September 2005

As part of a program of evaluating various speech compression systems, a group of new nonsense-syllable tests has been developed. Each test stimulus is a nonsense word of iambic form, in which the initial unstressed syllable is always /hə/ and the stressed syllable contains the phone or phones under test, in a specified phonetic context. A given test contains only a small number (10–20) of words, and is designed to provide a rapid evaluation of the performance of a speech communication link for only one or two consonant or vowel features. Thus, the test items in a given test consist of members of a given class of 4 to 8 consonants or vowels, and the subjects are instructed to restrict their responses to members of this class. In view of the short length of each test and the small size of each response ensemble, the tests are relatively easy to take, and the problem of learning a suitable phonetic transcription is minimized. Several types of speech-compression systems have been tested by these procedures, and some typical results are presented. [This work was supported by the Rome Air Development Center under contract No. 30(602)-2235.]
Measurement of Acoustic Impedance in Liquid-Piping Systems
Authors: Hixson E. L. , Kahlbau J. V. , Cousins E. L.
Published: September 2005

In the study of nondissipative wave filters for liquid piping systems, it is advantageous to know terminating impedances and the impedance characteristics of filter elements. A device for measuring these quantities has been built. It applies a sinusoidal volume velocity through the motion of a piston placed in contact with the liquid. Volume velocity is determined from measured piston motion and area; the resulting sound pressure is measured by a hydrophone. An electrodynamic driver produces the piston motion, and analogous acoustic impedance is calculated from the transducer voltages. The device calibration constant has been determined from transducer sensitivities and the piston area. The calibration has also been checked by measurements on known inertances. The device is described and examples of the information obtained by its use are presented. Applications include determination of water-borne sound velocity inside metal tubing, characteristic impedance of water inside pipes, filter-terminating impedance presented by laboratory piping systems, and characteristics of side-branch resonators.
Resonant Side-Branch Acoustic Filters for Liquid-Piping Systems
Authors: Hixson E. L. , Kahlbau J. V. , Bohls F. O.
Published: September 2005

Nondissipative side-branch acoustic filters for liquid-piping systems are discussed. Simple spring-mass resonators are used as branch elements. The filters are analyzed as distributed-parameter systems. One-, two-, and three-section filters are treated, and results of tests under both flow and no-flow conditions are given. Band-rejection characteristics are obtained with attenuations up to 40 db for no liquid flow. Under turbulent-flow conditions, effective attenuation is found to be reduced by noise regeneration.
Bending Vibrations of Inhomogeneous Beams and Systems of Beams
Authors: Heckl Manfred A.
Published: September 2005

This paper is concerned mainly with the vibrations of point-driven beams that have sudden discontinuities in material, cross section, etc. In such structures, an initially excited wave, such as a bending wave, will be partially reflected; but, there may also be a transformation into other wave types, such as longitudinal or torsional waves. It is shown how the impedance, the average transmitted power, and the propagation constant of a beam with one or more discontinuities can be calculated; the results are compared with experimental data. It is possible to extend the results to systems of beams such as grillages.
Methods for Characterizing Mounts and Materials
Authors: Schloss F.
Published: September 2005

It is convenient to characterize isolation mounts, materials, or simple damped structures to be used for reducing vibrations, by considering the element as a mechanical blackbox with two accessible points. If the motion of each accessible point is restricted so that it can be described by a single space variable, then the mechanical behavior of the blackbox (for example, its transmissibility or effectiveness) when placed in a system can be completely calculated if three impedances measured at the accessible points of the box are known. This three-impedance method for describing a mount has the advantage that it characterizes the mount itself independently of the system in which it is placed. The impedances chosen for measurement are the driving-point impedances of each end while the other end is blocked, and one transfer impedance, i.e., a ratio of force at a blocked end to motion at the driven end. At low frequencies, the transfer impedance also permits direct evaluation of the loss factor in the complaint material, even though the ends are sufficiently massive to complicate the driving-point impedances. Measurements of these impedances are presented for several standard Navy mounts and air mounts over the frequency range 10 to 2000 cps and static loads up to 5000 lb.
Extremal and Crest Statistics of a Square-Law-Derived Random Process
Authors: Smits T. I. , Smith D. A.
Published: September 2005

Theoretical expressions for the probability distributions of the extrema and crests of a square-law-derived random process ϖ=η+γη2 have been obtained, extending the work of R. H. Lyon and P. W. Smith, Jr., to larger values of the nonlinearity parameter γ. This theory gives the maximum, minimum, and crest distributions of the ϖ process for any η process once the maximum, minimum, and crest distribution densities of the η process are known. Particular emphasis is placed on the case where the η process is Gaussian. This covers, within the limitations of equivalent linearization, also non-Gaussian processes, say, the response of a hard-spring oscillator. Experimental data on the (bending plus tensile) strain-crest statistics for a clamped-clamped bar under tension vibrating in its fundamental mode are presented and compared with the theory. (This research was supported by the U. S. Air Force, AFSC Aeronautical Systems Division, Contract No. 33(657)-7453.)
Sound Propagation in a Random Medium by the Method of Bilocal Perturbation
Authors: Bourket R.
Published: September 2005

The method previously described (in Hughes Research Report No. 215) as bilocal perturbation theory is applied here to the calculation of the ensemble averaged acoustical-wave propagating through a medium with thermal inhomogeneities and with a turbulent velocity structure. For each of these types of perturbation, described by an appropriate autocorrelation function, a dispersion equation for the acoustic wave is derived and the attenuation coefficient calculated. The question of fluctuations is discussed briefly, and the procedure for carrying the bilocal treatment to a higher order is outlined.
Frequency Correlation of Sound-Transmission Functions in Rooms
Authors: Schroeder M. R.
Published: September 2005

Steady-state frequency responses between pairs of points in a room can be considered samples of a random process. (This holds for frequencies above a certain critical value, typically several tens of cycles per second.) The autocorrelation functions of frequency responses of a variety of rooms are computed analyitcally and compared with experimental data and Monte Carlo results. For rooms whose normal modes have uniform decay rates (exponential reverberation), the normalized autocorrelation function of the squared modulus of the frequency response depends only on the reverberation time T60 and equals [1+(0.455⋅T60⋅Δf)2]−1. The autocorrelation of the modulus itself has a more involved analytical form but, surprisingly, is almost equal numerically to that of the modulus squared. The autocorrelation and crosscorrelation functions of the real and imaginary parts of frequency responses are also computed. The practical significance of these frequency-correlation functions for room acoustics is discussed. The analytical methods employed can be extended to the computation of spatial sound-pressure correlation functions, including those of nondiffuse sound fields.
Utilization of Random-Response Information in the Determination of Structural Integrity
Authors: Leve Howard L.
Published: September 2005

A structural system is considered acted upon by several sources, each of which is of a random nature. Techniques are developed, and the type of instrumentation and data processing is established so as to determine the levels of statistical dependency of the various sources. These techniques permit a realistic evaluation of the response characteristics of a structure instead of considering, as is usual, that the sources have statistical behaviors which are either independent or completely dependent. In the process of these developments, the meaning of the crosspower spectrum in the real domain is established in contrast to the usual, purely mathematical, representation of this quantity in the complex domain. The fatigue life of the structural system under random loadings is then considered from the most recent, dislocation-oriented theory of cumulative fatigue damage developed by Valluri. Results from this theory for a structure responding in a narrow bandwidth are compared to those obtained by utilization of the Palmgren-Miner and Corten-Dolan cumulative-fatigue-damage theories. Equivalent sinusoidal-stress levels are given for each of the theories and are compared in view of results from available random-load fatigue tests.
Practical Systems for Quasi-Stereophony
Authors: Prestigiacomo A. J. , Schroeder M. R.
Published: September 2005

Artificial- or quasi-stereophony derives different multiple signals from a monophonic signal by means of (linear) filtering. The derived signals are then radiated from two or more separated loudspeakers. For certain filtering conditions and loudspeaker placements, a diffuse sound image is created which has the same “ambience” (spatial spread) as true stereophonic reproduction. Quasi-stereophony cannot, of course, duplicate the localization of true stereophony. However, it has been found that ambience, by avoiding the unrealistic impression that all sounds come from a small area, is as important to stereophonic-sound projection as the ability to localize correctly individual sound sources. Several practical systems for quasi-stereophonic reproduction are described. A new approach to artificial stereophony [J. Acoust. Soc. Am. 33, 1061 (1961)] using all-pass filters to avoid spectral distortions is demonstrated.
Loudspeaker Fidelity Contributed by the Reduction in Transient Distortion
Authors: Schlenker Vesper A.
Published: September 2005

The requirements for high fidelity in sound reproduction are discussed in relation to high-fidelity systems. A test method of rapidly recording the transient response of loudspeakers and 4-terminal networks containing transducers is described and illustrated. The transient-response curve is written automatically on the same chart as the conventional-response curve, decibels vs frequency. Hence, the transient-response curve appears below the conventional-response curve in varying db difference levels as the frequency changes. Characteristics of different types of conventional loudspeakers recorded by this method are presented. Thus, a powerful technique is provided for rapidly writing quantitatively the transient-distortion level throughout the frequency range of any loud-speaker or electrical network capable of generating transient distortion which detracts from naturalness in the reproduction of sound.
Effects of Certain Auditory Environments on Protensity
Authors: Dreher John J. , Evans William E.
Published: September 2005

Normal-hearing subjects estimated 1-, 2-, 4-, 8-, 16-, and 32-sec time durations under alternating conditions of quiet and four types of high-level ambient noise. Both duration-matching and independent estimates were investigated. Errors in quiet were commensurate with the results of previous investigations. Errors attributable to noise were unaffected by frequency of stimulus or response test tones, by varying lapse times following standard-duration tones in the matching studies, or by two of the four ambient interference noises. A significant monotonic underestimate of time duration was seen to attach to environments of intense, randomly gated, roving tone and to combinations of roving tone and square waves.
Discriminability of Differences in the Rise Time of a Tone
Authors: Tenney James C.
Published: September 2005

An experiment was conducted, using tones generated by the computer, to determine the just-noticeable differences in the rise time of a 1000-cycle pure tone with a duration of 1 sec, and with a linear (not exponential) attack, a steady-state portion, and a 100-msec decay. A forced choice, paired-comparison test was run with 10 different subjects. Fourteen different rise times were used, ranging from 2 to 50 msec. A clear time-order effect appeared which, although it is of considerable interest in itself, made the results of the test somewhat inconclusive. Still, a rough estimate of the results indicate that, within the range of rise times from 8 to 50 msec, the jnd approximates a constant proportion of a given rise time. Within this range, the smallest ratio of two rise times that can be judged correctly 75% of the time is roughly 3 : 2. Below this range (i.e., from 2 to 6 msec), the smallest difference that can be discriminated is 3 or 4 msec, so that the constant-proportionality relation no longer holds.
Effect of Reverberation on Reaction to Impact Noise
Authors: Thiessen G. J. , Subbarao K.
Published: September 2005

It has become customary to ascribe a subject's decreased tolerance to noise in a reverberant room to an actual increase in the sound-pressure level at the eardrum caused by the diffraction effect of the head for certain angles of incidence. However, a similar decrease in tolerance is observed if clicks are presented to subjects by means of earphones and if reverberation is added artificially. Four clicks per second, with artificially added reverberation, were presented to the subjects who, by means of a volume control, could adjust the level until it matched the same signal without reverberation. Matching was done according to “annoyance,” “noisiness,” and “speech interference.” Reverberation had no appreciable effect when the instantaneous rms level was below 45 db re 0.0002 d/cm2 (nor above about 135 db if extrapolation is relied on). The maximum effect occurred at 85 db, when matching to provide equal speech interference. The decreased tolerance caused by a reverberation time of 1.1 sec was then about 8 db. When matching according to “noisiness” or “annoyance,” the effect was only half as great or less. Only marginal effects were obtained with a reverberation time of 0.5 sec.
Acoustic Scattering from Fluid Spheres
Authors: Frey Harlan G. , Goodman R. R.
Published: September 2005

The problem of scattering of acoustic waves and pulses by fluid spheres immersed in fluid media is investigated for the case where the two media are very similar acoustically. This situation allows Taylor expansions to be used, and the results obtained for back-scattered plane waves are found to be much simpler than the exact results. The amplitudes and time dependences for back-scattered acoustic pulses to first order in the approximation can then be calculated. The result of considering higher-order terms of the approximation has not been fully investigated at this time. In the proper limit. the results obtained in the first-order approximation are compatible with Rayleigh scattering. but differ in the algebraic sign of the difference in density of the two media with the results obtained using the Born approximation.
Sonic Channels in the Atmosphere
Authors: Diamond Marvin
Published: September 2005

The mean-temperature profile of the atmosphere indicates the possible existence of two sonic wave guides in the atmosphere. Wind data above 30 km, which have become available recently through the use of meteorological rockets, have resulted in revised atmospheric-circulation patterns for the northern hemisphere. Wind data obtained from these patterns have been combined with mean-atmospheric-temperature data to determine seasonal sonic patterns of the atmosphere waveguide that can exist between the surface and an altitude of 50 km. These patterns indicate the existence of a strong sonic waveguide only for sound having an eastward-propagation component in winter and a westward-propagation component in summer. For other combinations of propagation directions and seasons, a waveguide does not exist between the surface and 50 km. The refraction of sound from upper altitudes to the surface will generally occur only in winter at sites located to the east of the source and in summer at sites located to the west of the source.
Driving-Point Impedance of Plates
Authors: McCormick J. R.
Published: September 2005

From an acoustic point of view, plates are “very soft” because of their many resonances. For instance, the average driving-point impedance of an aluminum plate 1/16 in. thick is equal to the impedance of a mass of 15 g at 1000 cps. The mechanical impedances of the driver and receiver frequently falsify the experimental results. Clamping also has a great effect on the variation of the driving-point impedance with frequency. At low frequencies, a considerable fraction of the vibration energy leaks out through the clamped edges, and the driving-point impedance is smaller than the computed value. At higher frequencies, it reaches the computed value when the clamping effectively isolates the plates from its surroundings. This paper shows that the driving-point impedance of a freely suspended plate, except for resonance peaks and antiresonance depressions, is independent of the frequency.
Theoretical Analysis of the Scattering of Sound by Elastic Cylinders of Moderate Wall Thickness
Authors: Horton C. W. , King W. R.
Published: September 2005

The echo structure reported by Barnard and McKinney [J. Acoust. Soc. Am. 33, 226 (1961)] can be explained theoretically by applying the Watson transformation to the usual expression for the scattered waves. The details of the analysis are given and the theoretical results are compared with the experimental results.
Amplitude Distribution of Broadband-Rectified and Finite Time-Averaged Gaussian Noise
Authors: Wittenborn A. F.
Published: September 2005

In acoustics, particularly underwater sound, it is often desirable to know the statistics of the amplitude distribution resulting from a finite time average of a rectified broadband noise (broadband in the sense that the bandwidth is comparable to or greater than the center of the band). Although the mean and standard deviation can be computed analytically for some input distributions, the output distributions have not been obtained. Some results are given for the case of a Gaussian input noise passed through a square-law rectifier followed by various amounts of averaging. These results were obtained by simulating the detection process on a computer. Comparisons of the results are made to several limiting cases which can be determined analytically and to some measurements which have been reported in the literature. (Supported in part by the Bureau of Ships.)
Study of [h] and Whispered Speech
Authors: Lehiste Ilse
Published: September 2005

The paper describes a study designed to investigate certain differences between phonated and whispered speech. A spectrographic analysis of 200 phonated and whispered words, spoken by five informants, revealed that whispered vowels differ from corresponding phonated syllable nuclei with regard to their formant positions, the distribution of intensity within the spectrum, and the dynamic structure of the syllable nuclei. A comparison of the whispered syllable nuclei with [h] in phonated and whispered words shows that the spectrum of [h] differs in measurable ways from that of whispered vowels. To study certain physiological differences between [h] and whisper, the rate of airflow was measured in the speech of five male and three female subjects. The rate of airflow during whispered speech was more than twice as high as that of phonated speech; the airflow during an initial [h] was more than six times as high as that during a following phonated syllable nucleus, and more than twice as high as that during a following whispered syllable nucleus.
Parameters of Vowel Perception
Authors: Lane Harlan
Published: September 2005

Psychophysical scales are determined for the amplitude, duration, and fundamental frequency parameters of vowels. Numerical estimates of vowel loudness and of vowel duration grow as a power function of their respective parameter values, while estimates of pitch are a logarithmic function of fundamental frequency. A given change in amplitude, duration, or fundamental frequency of a vowel appears greater to the speaker than to a listener; in other words, autophonic scales of vowel parameters grow more rapidly as a function of stimulus magnitude than do reception scales. When a subject is instructed to match his vocal response to a vowel stimulus, autophonic and reception scales of vowel perception predict the parameters of echoic responding. The matching function for each stimulus parameter shows some influence of the other parameters; the largest effect is the increase in response pitch associated with an increase in stimulus amplitude. This interaction is predicted quantitatively from a simplified analysis of the mechanics of the glottal source and from an empirical determination of pitch-amplitude relations in free responding.
Jet-Noise Suppression
Authors: Eldred Kenneth M.
Published: September 2005

This paper reviews the various basic concepts the suppression of jet noise through engine or nozzle design. The significant features of each concept are discussed in terms of simple jet-flow models which enable prediction of the noise-generation characteristics of the resulting jet flows. These jet noise-generation models, which are generally substantiated by existing data, are utilized to demonstrate optimum design trends and limits for future jet-engine designs. The results show that future jet engines can have significantly lower noise levels than current generation jets if noise becomes a major criterion for engine design at its inception. However, unless the noise-generation characteristics of the jet are considered at the earliest design stage, the possibilities for reduction of the eventual noise through nozzle modification are limited. [This work was supported by the U. S. Air Force under Contract AF33 (616)-5744.]
Physiological Noise in Relation to Audiometry
Authors: Shaw E. A. G. , Piercy J. E.
Published: September 2005

Low-frequency noise of physiological origin has been measured in a cavity enclosing the ear. The measurements were performed with a good condenser microphone resiliently mounted in a special enclosure of effective volume approximately 60 cm3 sealed to the head with a circumaural liquid-filled cushion. The over-all noise level in the enclosure and levels in certain bands rise and fall by a few decibels at the heart-pulse frequency, indicating that the noise is generated by the circulatory system. The level per 13 octave band averaged over six subjects is approximately 70 db re 0.0002 dyne/cm2 at 16 cps falling steadily to 34 db at 125 cps and 12 db at 250 cps. With the 12-cm3 effective volume of a TDH39 and MX41AR cushion, one would anticipate physiological noise levels 14 db higher than these or 48 db at 125 cps and 26 db at 250 cps. The levels per critical band might be somewhat higher yet. Since the tentative ISO hearing threshold levels at 125 and 250 cps are 49 and 27 db, respectively, one is led to suspect that these levels may have been raised by the masking effect of physiological noise.
Simple Vibrating Systems
Authors: Kauffman C. William
Published: September 2005

A study was undertaken to investigate the decay of simple electromagnetically driven mass-loaded systems by measurements of the bandwidth and of the decay time, where either the loss resistance or the loss factor was frequency-dependent. Results indicated, however, that it is extremely difficult to design a system that acts like a simple point-mass compliant-element vibrator. Unless great care is taken, the system does not produce the simple frequency curve that one would expect, but many resonances are observed that can be attributed to the system supports and the driving mechanism. Because of the difficulty experienced in eliminating the coupling to the supporting apparatus and the driver, a detailed study of simple vibrating systems became necessary. A series of mass-loaded systems that gave progressively simpler frequency curves was developed, including one in which the driving magnet acts as the mass loading. A description of each is presented, along with its frequency curve. [This work was supported by the U. S. Air Force Office of Scientific Research.]
Tapering a Bar for Uniform Stress in Lateral Oscillation
Authors: Bies David Alan
Published: September 2005

Approximate solutions are presented for the thickness and vibrational amplitude of a long thin bar vibrating in lateral motion under the condition of uniform stress along its length. It is shown that, rather than one unique shape dependent upon the choice of dimensionless frequency, there is a family of shapes that depends upon the choice of dimensionless stress. Attention is given to the problem of properly terminating such a bar. The predictions of the theory are compared with the results of experiment.
High-Frequency Acoustical Reverberation from a Rough-Sea Surface
Authors: Clay C. S. , Medwin H.
Published: September 2005

The scattering of high-frequency underwater sound (λ≪waveheight) from the sea surface is described in terms of two mechanisms: (1) conventional scattering theory for a rough surface with normally distributed slopes appears to predict adequately the backscattering at incidence near normal; (2) a rather low population of near-surface resonant bubbles would suffice to explain the behavior at angles near grazing. The two effects are used to interpret the experimental surface-scattering data at high frequencies for all angles of incidence. [Hudson Labs. Columbia Univ. Informal Doc. No. 55.] [Work supported by the U. S. Office of Naval Research.]
Physical Theory for the Reverberation Observed in Backscattering
Authors: Saenger R. Alfred
Published: September 2005

The Kirchhoff approximation has been used in deriving the reverberant tail ps, which results when a short spherical pulse of strength F(t) backscatters from a rough pressure-release surface. The amplitudes of the differential scattered pulselets producing ps depend on the displacement and slope of the surface elements at which they originate, the functional form of both F and F′, and also certain geometric weighting factors determined by the location of the elements. More-specific insight is obtained from hs, the component due to scattering in the impulse response h = h0 + hs, of the “ocean-surface filter.” The tail portion of hs may be expressed as a “ring average” of two terms, one of which involves the slope, the other the curvature of the surface. Near the specular region, the term involving slopes is dominant generally; later, the curvature term gains the upper hand. Specific calculations of 〈ps2〉uv for incident sine-wave pings and explosive pulses reflecting from randomly rough surfaces are compared with recent experimental work of various investigators. [Work supported by the U. S. Office of Naval Research.]
Underwater Sound Reflection from a Pressure-Release Sinusoidal Surface
Authors: Barnard G. R. , Bardin J. L. , Cordaro J. T.
Published: September 2005

Experimental curves are presented that describe the reflected sound field from a pressure-release sinusoidal surface. The measurements were made in an 8-ft-diam, 7-ft-deep laboratory tank equipped with a dual-transducer-positioning system that is capable of positioning each transducer to any position in the tank with an accuracy of ±0.003 in. in any x, y, or z coordinate and ±0.1° in tilt and azimuth. The sinusoidal surface was machined in styrofoam sheets that were glued to a 4×4-ft tray located near the bottom of the tank. The sinusoid was cut with an amplitude of 1.5 cm and a period of 4.5 cm. The amplitudes of the reflected pulses are presented as a function of the angle of reflection for several fixed grazing angles. Amplitude data are also presented as a function of frequency for several fixed grazing angles. Zero-order or specular-reflection data are presented for incident wavelengths varying from 1 to 14 the amplitude of the sinusoidal surface. [Work supported by the U. S. Navy Bureau of Ships.]
Electromyographic Study of the Coarticulation of Vowels and Consonants
Authors: MacNeilage Peter F.
Published: September 2005

By what mechanisms is a given phone produced in various phonetic contexts? Electromyographic studies of articulator action have been made to provide data bearing on this question. An earlier study attempted to specify the relation between observed myographic activity and tongue movement when a subject produced vowels in a “neutral” ([p]-vowel-[p]) context. In this study of the same subject, the four vowel nuclei [i], [u], [æ], and [ɔ] were spoken with all possible combinations of the lingual consonants [t] and [k], in CVC monosyllables. Muscle potentials were recorded from 5 sites spaced evenly along the dorsal surface of the tongue and one ventral site near the tongue tip. In many cases during vowels, voltage levels either increased or decreased as compared with levels seen in the neutral context. Some of these changes suggested that muscles can produce (a) increase in tongue movement in the same direction as that required for the following phone, or (b) decrease in movement if the following phone requires a contrary movement. Other features of the motor control of coarticulation are also illustrated and discussed. [This investigation supported in part by Public Health Service research grant No. DE 01774 from the National Institute of Dental Research, National Institutes of Health, U. S. Department of Health, Education, and Welfare.]
Statistics of Spoken American English
Authors: Carterette Edward C. , Jones Margaret Hubbard
Published: September 2005

As part of a long-term study on the growth of patterning in children's language, a considerable body of spontaneous speech was collected from children in grades 1 through 5 and from adults. The speech was recorded with a pair of condenser microphones on two tracks. Phonetic transcriptions were made using a 41-symbol alphabet. Editing and normalization were shunned so that the statistical analysis could be used in studies of speech perception, learning, psycholinguistics, and linguistic structure. Phonetic transcriptions were analyzed by digital computer. The major data are (1) frequency distributions of singlets, pairs, and triplets, (2) mean phonetic “word” and “sentence” length, (3) the Markovian information in the sequential constraints of successive pairs and triplets, and (4) various distributions induced on the basic ones by linguistic rules, e.g., place and manner of articulation, stress, and intonation. Comparisons show the free speech of children and adults to be remarkably similar both in the distribution of units and in sequential structure. Implications of our findings for research in speech and psycholinguistics are discussed. [Work supported by the U. S. Department of Health, Education, and Welfare.]
Atmospheric Infrasonic-Pressure Variations
Authors: Richie William C. , Hixson E. L.
Published: September 2005

The pressure variations of the atmosphere at White Sands Missile Range, New Mexico, were recorded, using a solion infrasoniC microphone array. The dimensions of the square array were 10 000 ft per side. The solion infrasonic microphone monitored data in the pressure range of 0.1–500 dyn/cm2 and in the frequency region of 0.033–50 cps. Measurements were made during high winds (20–30 kt) and very low winds (0–2 kt). The statistical nature of the infrasonic atmospheric-pressure data obtained is presented by the use of probability density functions, autocorrelation functions, crosscorrelation functions, power spectra, and crosspower spectra. [This work sponsored by the U. S. Army Electronics Research and Development Activity, White Sands Missile Range, N. M., under contract DA 36-039 SC-90719.]
Effect of Phase Difference between Signal and Masker on Detection of a Narrow-Band Noise Signal
Authors: Rilling Mark E. , Jeffress Lloyd A.
Published: September 2005

In a comparison of tonal and narrow-band signals, reported by the authors in 1964, the masking level differences (MLD's) for the two signals were the same for corresponding phase shifts. Earlier, Hirsh and Webster reported differences for similar conditions. In the authors' experiment, there was a random phase difference between the signal and masker since separate noise generators provided the signal and noise, while Hirsh and Webster's single noise generator gave a fixed phase difference between the signal and masker. In the present experiment, a single noise generator was used and the phase difference between the signal and masker was shifted in phase by 30° steps between 0° and 180°. For each signal-masker phase difference, the signal was presented in phase at the ears and reversed in phase at one ear. Data are presented as MLD's relative to the signal-in-phase condition for each signal-masker phase difference. The MLD's increase monotonically from 13 dB at 0° to 18.5 dB at 180°. [Work supported by USN Bureau of Ships contract NObsr-72627 and under a grant from the National Aeronautics and Space Administration R-129 through ONR contract 3579(04).]
Masking-Level Differences for Lateralization of a Weak Signal
Authors: Egan James P. , Benson William
Published: September 2005

When a strong signal is presented monaurally, listeners can easily lateralize the sound. If noise is present in both ears, uncertainty of lateralization may result. This uncertainty was measured over a range of signal energies under release from masking (N0) and without such release (NU). In the main experiment, the signal (500 cps, 0.25 sec) was always presented during the single interval of each trial to either the right or the left ear by random determination. Listeners responded “right” or “left.” Detection using N0 and NU was also determined, and the listeners knew that the signal occurred in only one ear over a series of trials. Measures of detection were secured by two methods: (1) single interval, yes-no, and (2) two-alternative, temporal forced choice. The MLD (N0 versus NU) for detection was about 9 dB. For lateralization, the MLD was only about 4 dB. With NU, d′-type measures for lateralization are only slightly inferior to those for detection. Detection is about the same with or without ear uncertainty. [Work supported by the U. S. Air Force Office of Scientific Research.]
Masking-Level Differences as a Function of Interaural Disparities in Intensity of Signal and of Noise
Authors: Egan James P.
Published: September 2005

A marked release from masking, or masking-level difference (MLD), results when a sinusoid is presented monaurally Sm rather than binaurally and in phase S0 with correlated (in phase) noise N0. If the sinusoid in one ear, rather than being removed entirely, is reduced in intensity relative to that in the other, a smaller MLD should result. MLD's were determined as a function of the ratio of the energies of the right- and left-ear sinusoids. This signal (500 cps, 0.25 sec) was presented in one or the other of two temporal intervals against a background of white noise N0. Also, MLD's result when Nm-Sm is changed to N0-Sm. Thus, MLD's were determined as a function of the relative intensity of the noise in the nonsignal ear with noise correlations of N0, Nπ, and NU. For N0, there is some release from masking even when the noise in the nonsignal ear is as much as 40 dB down from that in the signal ear. [Work supported by the U. S. Air Force Office of Scientific Research.]
Uncertain Signal Detection with Contralateral Cues
Authors: Sorkin Robert D.
Published: September 2005

A series of auditory signal-detection experiments was run under conditions of signal-parameter uncertainty. This uncertainty was effected by allowing one signal parameter, either signal frequency or signal starting time, to vary randomly across the sequence of experimental trials. These experiments, run monaurally, employed a simple yes-no detection procedure, signal plus noise occurring on half of the trials and noise alone occurring on the other half. A series of comparison experiments using the same observers was run under identical conditions, with the addition of a simultaneous cue signal in the contralateral ear. This cue was present on both signal and no-signal trials and was identical to the signal that might have been presented to the detecting ear. The results clearly demonstrated (a) the previously noted result, that a simultaneous contralateral cue degrades performance at high signal-to-noise levels; and (b) a new result, that at low signal levels such a cue facilitates performance of the detection task. The degrading effect is a function of the cue-signal energy. The resulting psychometric functions suggest an interpretation in terms of a crossmasking and uncertainty-reduction hypothesis. Similar interpretations are indicated for crossmodality experiments.
Determination of Traveling-Wave Velocity in the Human Cochlea
Authors: Zerlin Stanley , Causey G. Donald
Published: September 2005

When two equally loud tones of somewhat different frequency are pulsed in exactly the same way and presented dichotically to a listener, a single coherent tonal image can be heard lateralized toward the higher-frequency side. When the higher-frequency signal is delayed an appropriate amount, the sound image is brought to the midline. According to place theory, the two different frequencies are now arriving simultaneously at their designated “places” on the cochlear partition. A number of such tonal pairs were used to determine traveling-wave velocity along various short segments of cochlear partition. The average of three trained listeners showed wave velocity decreasing from about 30 m/sec on the higher-frequency portion of the partition to approximately 0.1 m/sec at the low-frequency end. Our results are compared to some findings and formulations provided by other authors. [Work supported by grant NB 03229-02 from the National Institutes of Health, U. S. Department of Health, Education, and Welfare.]
Marine-Sediment Attenuation and Ocean-Bottom Reflected Sound
Authors: Cole B. F.
Published: September 2005

The frequency dependence of ocean-bottom reflectivity has stimulated an interest in the relation between frequency and marine-sediment attenuation in the ocean bottom. In this paper, evidence for a linear frequency-attenuation relation is derived from a comparison of theoretical and measured reflection coefficients for a frequency region of 100–4800 cps. The reflection process was simulated by a 3-layer fluid model with attenuation in the second and third layers. Theoretical reflection coefficients were generated, considering the sediment attenuation proportional to the one-half, first, and second powers of the frequency, and were compared with the measured coefficients. It was concluded from this study that the frequency dependence of ocean-bottom reflectivity can be reconstructed theoretically if the marine-sediment attenuation is assumed to be proportional to the first power of the frequency.
Acoustic Properties of Sediments
Authors: Hampton L. D.
Published: September 2005

This is a summary of work done at DRL on measurement of acoustic properties of water-saturated sediments. The sediments used were laboratory-prepared to allow control of physical parameters (such as grain size, volume concentration, compressibility, etc.) and to approximate natural sediments. Acoustic velocity and attenuation in the sediments were measured over the frequency range 4–600 kc/sec. Acoustic measurements were made at high frequencies by means of two probes inserted in the sediments and at low frequencies by means of a specially constructed rigid-wall standing-wave tube. The data presented show the frequency dependence of attenuation and velocity in the laboratory-prepared sediments and the change in this frequency dependence with changes in physical parameters of the sediments. Sediments composed of pure clay or clay and sand up to 15% (by weight) show a f1.37 frequency dependence of attenuation. Sediments with greater than 30% sand (by weight), including pure sand, exhibit an f0.5 frequency dependence of attenuation. The measured dispersion is approximately 6% over the frequency range 4–600 kc/sec. Velocity increases with frequency. [Work sponsored by U. S. Navy Bureau of Ships.]
Studies of Observed and Predicted Values of Bottom Reflectivity as a Function of Incident Angle
Authors: Menotti F. R. , Schumacher W. R. , Santaniello S. R.
Published: September 2005

Using a deep source and deep receivers, measurements of the acoustic reflectivity of the ocean bottom at 1 kc/sec were made at an area in the Atlantic Ocean. The data, that is, the direct and the first-order bottom-reflected arrivals, were acquired digitally at sea and have been reduced via a computer program. The program computes the reflection coefficients based on peak pressure as well as the time-integral square of the pressure. The computer analysis also furnishes the travel time of each arrival, horizontal range, and incident angle for each transmission. The total number of data points considered exceeds 4000. Computations based on velocities, densities, and attenuations that have been obtained from an analysis of cores taken in the general area of the acoustic tests have been performed, using a theoretical model of the bottom. This model consists of many absorbing liquid plane parallel layers over one absorbing semiinfinite solid. Comparisons of the experimentally derived reflection coefficient as a function of incident angle are made with those obtained from the model, and the relevance of the complicated layering structure and attenuation of the bottom is discussed.