bluuebunny/crossref_metadata_2025 huggingface dataset:
Short-Term Loudness Changes
Authors: Small Arnold M.
Published: November 2005

In a previous study, it was reported that in a forward masking situation loudness changes as measured by a median plane lateralization of the apparent sound source were vanishingly small [J. Acoust. Soc. Am. 38, 928 (1965)]. This observation was somewhat surprising in view of the large threshold shifts seen using the same stimulus conditions. The present paper reports attempts to resolve this apparent paradox. The task of the six listeners was twofold: (1) to adjust the level at one ear of a binaurally presented test signal so that its sound image was congruent with an identical standard (except for the standard's fixed SPL). An adapting stimulus was interposed between the standard and the test signals. (2) The livel of both test signals was simultaneously adjusted so that their combined loudness was equal to that of the standard. The lateralization results show shifts of more than 20 dB with recovery proceeding nearly exponentially and being complete in 100 msec. The smallest shifts were observed at 1000 Hz with larger amounts at 250 and 4000 Hz. The direct loudness measures showed similar results, although they were smaller in magnitude. [This research was supported by National Science Foundation.]
Intonation: Accent and Emphasis, Cadence, and End-Glide
Authors: Vanderslice Ralph
Published: November 2005

Lieberman's (1967) simplistic model of American intonation is wrong on three crucial counts: (1) it attributes most pitch change to variations in subglottal pressure, whereas EMG and cricothyrometry show that laryngeal adjustment is the primary physiological correlate; (2) it recognizes only one degree of prominence, whereas systematic synthesis requires accent [essentially Trager and Smith's primary and (prenuclear) secondary “stresses”] and emphasis (usually “overhigh” but with variants including Bolinger's “ac ent C”); (3) it conflates postnuclear pitch cadence with terminal pitch endglide although the domain of the former under context-dependent accent shift may be a whole order of magnitude longer than the postulated 150–200 msec. Distinguishing these sometimes overlapping gestures permits orderly treatment of traditional tunes in terms of binary features: unmarked (upward-obtruded) nuclear accent or emphasis may be followed by falling or nonfalling cadence (±Fall) with rising or nonrising endglide (±Rise). Intonations then are falling [+F, −R], rising [−F, +R], falling-rising [+F, +R], and sustained [−F, −R]. Major and minor types are distinguished by a third feature, ±Pause. [Work supported by Office of Naval Research.]
Phonemic Confusion in Whistled Turkish
Authors: Bastian Jarvis , Wall Carol
Published: November 2005

A method of whistling the local Turkish dialect has been developed in Northeastern Turkey that involves whistling while executing approximations to the standard articulator maneuvers of the spoken dialect. The signals produced are sufficiently intense and intelligible to those who have learned to use this signaling system to provide an auxiliary means of linguistic communication over long distances in the rugged terrain they inhabit. This system of “whistled speech” is very similar to those that have been recorded in much the same ecological conditions in one of the Canary Islands and in the Pyrenees. However, the Turkish system is based on a far richer phonemic inventory than the others, which are based on Spanish dialects. We therefore analyzed the effectiveness of the Turkish system in transmitting the phonemic contrasts maintained in the spoken language. Confusion test results indicate a severe reduction in the phonemic contrasts transmitted in the whistled version. The nature of these confusions and of their acoustical basis is discussed together with their consequences for sentence intelligibility. [Field work supported by Wenner-Gren Foundation.]
Automatic Speaker Authentication Using Speech Recognition Techniques
Authors: Meeker W. F. , Martin T. B , Herscher M. B. , Phyfe Douglas , Weinstock Martin
Published: November 2005

While some degree of speaker recognition can be achieved using gross measures such as average glottal frequency or average spectrum, it seems certain that, for highly accurate speaker recognition or authentication, it will be necessary to know what is spoken. In applications where there is no control over what the speaker utters, automatic speech recognition becomes a prerequisite for automatic speaker authentication. Considerable success in automatic speech recognition has been achieved using analog-threshold logic and this equipment has been used to select automatically portions of continuous speech for speaker authentication. Characteristics of continuous speech deviate substantially from those predicted by classical phonetics and many of these deviations can be used for speaker authentication. A number of different measures have been studied and automatically extracted. For vowels, the basic measure is the slope of the spectrum. For consonants, spectral characteristics, duration, and sequence of occurrences are useful measures. The over-all accuracy of authentication can be quite high when results for many individual measurements are combined. Results for single and multiple measurements will be discussed. [Work sponsored by the U. S. Army Electronics Command.]
The Variability of Bottom Reflected Signals Using the Deep Research Vehicle ALVIN
Authors: Breaker Laurence C. , Winokur Robert S.
Published: November 2005

Two dives were made using the deep research vehicle ALVIN to investigate the variability of normal incidence bottom reflected signals at 12 kHz. The measurements were made over a locally smooth bottom in a water depth of about 4700 ft in the tongue of the ocean. Approximately 800 bottom reflected signals were recorded while ALVIN hovered at three levels above the ocean bottom; 500, 2000, and 4500 ft. For each depth, frequency distributions, atuocorrelation coefficients, and coefficients of variation were computed using both relative peak amplitude and energy levels. The results indicate that significant changes in bottom reflectivity can occur in a short duration and that the observed variations are probably cuased by changes in the reflective characteristics of the ocean bottom as the vehicle drifted in a horizontal direction. Changes in the bottom are suggested by the data collected at the deepest level, which exhibits a pronounced shift in signal level and a bimodal frequency distribution of pulse amplitudes. In addition, the observed fluctuations generally increase with increasing distance above the bottom.
Amplitude Stability of Bottom Bounce Sound Propagation in the Hawaiian Area
Authors: Fisher F. H.
Published: November 2005

Measurements of the coefficient of variation have been made of short (5 msec) 5.5 kHz pulses at a range of 5.5 mm in about 2500-fathom depth at position 18°58′ N and 156°16′ W. Pulses received at hydrophones mounted on FLIP at 300-ft depth show the bottom-bounce path to be highly stable compared to the waterborne. Photographs of the received pulse structure as well as numerical data will be presented.
Surface Reflection Modulation of an Underwater Explosion Spectrum
Authors: Christian Ermine A.
Published: November 2005

For a simple harmonic source near the surface of the ocean, the interference pattern of direct and surface-reflected waves is described by the well-known Lloyd mirror dependence. With a pulse source, such as an underwater explosion, the interference effect is a modulation of the original pulse spectrum by a factor that depends upon frequency and the space variables. When the source and the receiving hydrophone remain at constant (though not necessarily the same) depths, both the amplitude and the period of the modulation term increase with increasing range. Depending upon the burst-receiver geometry and the reflectivity of the surface, at some frequencies the spectral energy level of the direct wave might, theoretically, be increased by as much as a factor of 4. In this paper, predicted differences between the original and the surface-modulated pulse spectrum are shown for several geometries and reflectivity coefficients, and are compared with measurements from small underwater explosions. [This work was supported by the Advanced Research Projects Agency.]
Influence of Hollow Shells on the Porosity-Sound-Velocity Relationship in Some Marine Sediments
Authors: Gallagher James J.
Published: November 2005

Representative clean globigerina tests were constructed from available data, and internal void volumes were computed. For a median grain size of 0.5 mm, a value of 45% was assigned to the interstitial porosity. The effect of adding a computed fluid-filled internal porosity of about 80% is to produce a mean bulk porosity of 60%, or a change of 15% from that of a solid grain aggregate. If the packing of solid and hollow particles of the same uniform size and shape is similar, the degree of grain-to-grain contact and of interstitial porosity is similar. Therefore, sound velocity through these uniform aggregates should be of comparable value. However, the addition of internal porosities of the hollow shells offsets the porosity versus sound-velocity relationship. Porosity values for the high-carbonate hollow shells should be reduced by 15%–20% to fit the sound velocity versus interstitial porosity curve. [Data obtained from the Marine Geophysical Survey substantiate the results of these preliminary computations.]
Ultrasonic Image Systems for Nondestructive Testing
Authors: Berger Harold
Published: November 2005

Ultrasonic imaging techniques are finding increased application in the medical and industrial fields because the image presentation often offers the advantage of improved interpretation capability for the ultrasonic test. In the nondestructive testing field, ultrasonic imaging inspection methods have recently been expanded to include television techniques; the operation and application of these techniques are emphasized in this report. In addition to interpretation advantages, television methods can also present improved resolution capabilities and faster inspection speeds, as compared to other ultrasonic inspection methods. Continuous-wave ultrasonic television systems have shown promise as inspection methods for relatively thin, flat material in which inspection is desired to determine such things as bonding, particle size variations, or homogeneity. Flat, reactor fuel plates and thin metal spot welds are examples of materials for which this type of inspection has been shown to be useful. Pulsed inspection systems have also been demonstrated, with relatively slow image presentation rates. These systems, when further developed, offer promise for greater range of application. [This work was performed under the auspices of the U. S. Atomic Energy Commission.]
An Underwater Acoustic “Television” System
Authors: Haslett R. W. G.
Published: November 2005

It may not be widely known that, over the period 1949–1954, an experimental model of a closed-circuit underwater acoustic “television” system for use in muddy water, was developed in the United Kingdom under an Admiralty contract. The object to be viewed was irradiated with ultrasonic waves and a real acoustic image of the object was formed by a concave mirror. A special converter tube, rather similar to a television camera, transformed the image to a television picture. Two programs of work were pursued side by side: (a) the development of the image converter tube and electronic circuits, and (b) the design of the mirror assembly. Subsequently, the whole system was subjected to detailed investigation in a water tank and at sea, to determine the resolution, the maximum range obtainable and the appearances of a number of objects having simple shapes.
Utilization of the Liquid Surface Levitation Effect as a Means of Ultrasonic Image Conversion for Materials Inspection
Authors: Gericke Otto R. , Grubinskas Robert C.
Published: November 2005

An ultrasonic image conversion cell utilizing the liquid surface levitation effect has been developed. This effect is based upon the principle that the surface of a free liquid will be deformed in accordance with the cross-sectional intensity distribution of an impinging ultrasonic beam. The image conversion cell has been successfully applied for nondestructive testing purposes. It can be coupled directly to an ultrasonically excited test specimen to obtain characteristic liquid-surface relief patterns depicting internal discontinuities. A significant advantage of the conversion cell is the fact that it does not require the test specimen itself to be immersed in a liquid. Also, because the conversion cell produces a “real time” image, pulsed, frequency-modulated, and continouus-wave modes of ultrasonic excitation can be used, and thus, various types of ultrasonic images can be obtained.
Visual Tracking of Auditory Stimuli
Authors: Stream R. W. , Whitson E. T. , Honrubia V.
Published: November 2005

Inside an anechoic chamber electro-occulographic techniques were used to record the eye movements in 20 subjects who were requested to track with their eyes a steady and continuously moving auditory stimulus. A motor-driven rotary switch made successive contact with 24 loudspeakers mounted side by side in an arc 180° wide and 11 ft in diameter. At angular sound velocities ranging from 15°–180°/sec, the eye movements were recorded under conditions of light and darkness. As the angular velocity of the stimulus increased, the horizontal displacement of the eyes decreased from an average maximum amplitude of 90°–60°. At low velocities, the eye movements followed precisely the position of the sound source. At high velocities (i.e. larger than 130°/sec) mostly saccadic movements were produced. The tracking ability of the eye, judged by the qualitative analysis of the recorded movements, was better in tests performed in the light rather than in darkness.
Signal Characteristics of the Calls in the Bullfrog's Vocal Repertoire
Authors: Capranica Robert R.
Published: November 2005

The vocal repertoire of colonies of bullfrogs maintained in a seminatural environment in the laboratory consisted of a distinct set of stereotyped calls: (1) mating calls made only by males; (2) three types of calls involving territorial behavior—one type made only by males, one type made only by females, and a third type made by both males and females; (3) release calls made by both sexes; (4) warning calls made by both sexes; and (5) distress calls made by both sexes. Each call is characterized by a different gross temporal pattern. The periodicity of the temporal fine structure is different for each type of call, with the mating call having the highest periodicity (100/sec). The spectral distribution of energy in each call is concentrated in the range 200–2000 Hz. The bullfrog's auditory system is well suited to detect and encode the temporal and spectral features of the acoustic waveforms in these calls.
Auditory-Nerve Responses as a Function of Repetition Rate and Background Noise
Authors: Teas Donald C. , Henry Gretchen B.
Published: November 2005

Auditory nerve responses to 2- and 6-kHz tone pips were analyzed for changes in magnitude and latency. The signals were presented at repetition rates from 2/sec to 160/sec with and without background noise present. The bandwidths of the noises and signals were identical, although unlike signal and noise were also paired. The responses to the 2-kHz pip presented at 2/sec in weak 2-kHz background noise showed an increase in magnitude as compared to the no-noise condition. The responses to the 6-kHz pip showed a similar increase in magnitude for increases in repetition rate up to 10/sec. However, at 10/sec, 6-kHz background noise was maximally effective (over-all repetition rates) in reducing response magnitude. Associated with response enhancement was a decrease in peak latency. Stronger noise and faster repetition rates increased the latency and decreased response magnitude. [This research was partially supported by PHS grant.]
Neurological Activity During Threshold Tracking in the Cat
Authors: Saunders James C.
Published: November 2005

Cats were trained to track auditory thresholds to a 1.0- and 2.0-kHz tone, acoustic clicks, and electrical pulses delivered to the cochlear nucleus. The frequency-synchronized discharges produced by the tonal stimuli were monitored at the cochlear nucleus with a wave analyzer as the animal reached its behavioral threshold. A direct empirical relationship was observed between the behavioral threshold and the amplitude of neural activeity detected at the cochlear nucleus. Evoked potential discharges were monitored at the auditory cortex as experimental animals tracked a behavioral threshold to transient stimuli. The results suggest that the absence of cortical activity is highly correlated with the inability to perceive the stimulus. The relationship between neural activity and the behavioral threshold indicate that: the amplitude of neural activity is directly related to the perception of loudness.
Source Size as a Theoretical Limitation on the Determination of Wave Vectors by Detector Arrays
Authors: Posmentier Eric
Published: November 2005

An important class of infrasonic waves in the atmosphere and seismic waves in the earth's crust are generated by ocean waves in marine storms. The determination of wave vectors from such large sources by detector arrays, is limited by the decrease in resolution, ambiguities, and systematic errors introduced by the large sources, as well as by the resolving power and ambiguities associated with a given array configuration. The apparent phase lag and coherency between two detectors, each receiving signals from the multitude of mutually incoherent oscillators comprising a large source, is discussed as a function of source size, and source-detector configuration. Several examples of source-array configurations are discussed, and calculated values of the discrepancies between apparent wave vectors and wave vectors from the source centers are presented. Empirical results are presented to confirm the validity of this approach in the case of microbarom generation by ocean waves.
Experiments on the Use of the Touch-Tone Telephone as a Communication Aid for the Deaf
Authors: Nelson J. R.
Published: November 2005

Two methods are described for using the Touch-Tone telephone as a communication aid for the deaf. Both methods depend upon the calling party spelling the message to the deaf receiver using a previously agreed upon code. Both methods also require circuit attachments to the conventional Touch-Tone telephone set of the receiver. In the first method, an auxiliary Touch-Tone dial is available at the receiver. Depressing a Touch-Tone button at the transmitter causes the corresponding button to light on the receiver's auxiliary dial. The auxiliary circuitry for visual presentation at the receiver includes standard Touch-Tone decoding filters and simple AND gates. The second method utilizes the same transmission technique but has more sophisticated circuitry at the receiver to accomplish the multiple-character decoding automatically. In this case, the visual presentation is the alphanumeric character which was transmitted. Experiments are described on the speed and accuracy with which these techniques can be used. Typical communication speeds are 4 words/min for the first method and 8 words/min for the second method. Both methods yield comparable error percentages, on the order of 0.2% .This performance is achieved without special training or skill.
Effects of Delayed Sidetone on the Speech of Aphasic, Dysarthric, and Mentally Retarded Subjects
Authors: Singh Sadanand , Schlanger Bernard B.
Published: November 2005

Duration, amplitude, and phonetic errors were measured to test the effects of delayed and normal sidetones on the speech of 10 aphasic, 10 dysarthric, and 10 mentally retarded subjects. Additional variables included structurally correct semantically real and unreal kernel, negative, query, and negative-query sentences. Tested were the differences between the three groups of subjects under conditions of 0.18-sec delay and normal delay in sidetone, three degrees of grammaticalness, and the four syntactic classes. The delayed sidetone affected the mentally retarded and dysarthric subjects more than the aphasics. The ratio between the duration under the 0.18-sec delayed sidetone and normal sidetone conditions for aphasic subjects was 1.20:1, for dysarthric 1.62:1, and for mentally retarded, 1.72:1. The grammatical sentences were affected less than the ones with unreal verbs. Sentences with unreal nouns, verbs, and objects were maximally affected. The grammatical classes were affected from least to the most in this order: kernel, query, negative, and negative-query.
Differential Effects on Underwater Hearing Thresholds of Air and Water Interface with the Tympanic Membrane
Authors: Hollien Harry
Published: November 2005

Thresholds of human hearing were obtained underwater for two conditions: (1) with the external auditory meatus completely water filled and (2) with a bubble of air trapped against the tympanic membrane. The first condition was accomplished by an otolaryngologist forcibly irrigating the external meatus underwater; the second by placing plugs in the ears in order to encapsulate air in the meatus until the head was underwater and the test (with the plugs removed) initiated. Subjects were seven divers who were tested in DICORS at a depth of 12 ft. Threshold SPL's were obtained freefield by the Békésy technique for the frequencies 125, 250, 1K, 2K, and 8Hz. Threshold shifts (re: air) for both conditions of underwater hearing were consistant with those previously reported. SPL's for the two experimental conditions were virtually identical for all frequencies except 250 Hz where hearing was 6dB better for the water-filled meatus condition. Statistical analysis (AV) of the data showed lack of significance at the 5% level of confidence. [The project was supported by the Office of Naval Research.]
Objective Procedure for Reading VU Meters
Authors: Levitt Harry , Bricker Peter D.
Published: November 2005

Speech level measurements obtained with a VU meter are subject to several sources of variability. The measuring procedure outlined here is designed to reduce variability introduced by the meter reader and so provide a reading more representative of average speech level. A sampling procedure is used in which controlled illumination renders the meter pointer visible only during brief intervals. Each time the dial is illuminated, the meter reader is required to determine whether or not the pointer exceeds a given deflection. If the pointer exceeds the critical value, the speech signal is attenuated by a fixed amount before the next trial. If the pointer lies below the critical value, the attenuation is reduced for the next trial. An up-down procedure with a regularly decreasing step size is used. The technique is such that the attenuation level converges rapidly on that value at which the pointer exceeds the critical value a fixed proportion of the time. Measurements obtained with this procedure have been found to be highly repeatable and relatively free of intersubject differences.
New Artificial Voice and Applications
Authors: Carlisle Richard W.
Published: November 2005

The artificial voice to be described is an elaboration of the WE 555 Speaker and coupler utilized in current Standards. A felt damper pad and an acoustic tube load, with damping in the tube, have been added. These lower the resonant frequency and smooth midrange and high frequencies. The mouth is oblate in shape. The distance from the felt damper, and the effective area of the sound passage to the mouth, are estimated to be of the same order of magnitude as corresponding portions of the human vocal tract. Application of this artificial voice to sound radiation from a simply proportioned plastic face are described, together with application of the ensemble to measurements within an oxygen mask.
Ohm's Law and Masking
Authors: Cardozo B. L.
Published: November 2005

The harmonics in the spectrum of a periodic pulse train should, according to Ohm's law, be audible separately. When trying to check this one meets two difficulties in terms of subjective spectrum analysis. First, the nth harmonic may be masked in part or completely by other harmonics. Second, even if the nth harmonic is not masked completely, one has find it among a great many others. Makins use of “Schouten's artifice” (alternatively suppressing and reintroducing the nth harmonic), these difficulties can be lessened. Once the nth harmonic is heard, one may determine its masked threshold by attenuating it. Using the method of adjustment, three experienced subjects measured the masked thresholds of the lowest 10–25 harmonics of a 50, 100, 200, and 400 Hz periodic pulse train at 30 dB SL. From these measurements masking curves are derived. The slopes of these curves show reasonable agreement with those of earlier investigations. A feature of the present method is that one need not make use of noise and still is able to determine masking of closely adjacent frequencies. In varying the time interval, the experment also shed some light on the dynamics of masking.
Detection of Tones in the Absence of External Masking Noise
Authors: Watson Charles S. , Franks John R. , Hood Donald C.
Published: November 2005

Sound pressures required for various levels of detection performance, in the absence of external masking, are summarized in iso-detectability contours. Each such contour shows, for frequencies from 125 to 4000 Hz, the SPL of 150-msec tone pulses which yield a specific probability of correct decisions in a two-alternative, temporal, forced-choice psychophysical procedure (2ATFC). Detection in the absence of externally introduced masking noise is found to differ in no qualitative ways from that in the presence of noise. Additional results suggest a spectrum of “internal noise” which is essentially a critical ratio below the sound pressure level of low-detectability (d′ = 1.0) tones in the quiet. Iso-detectability contours for detection performance of 55% and 99% correct in the 2ATFC procedure are found to enclose the range of sound pressure levels currently accepted as audiometric zero (ISO). [Work supported by the National Institutes of Health, Public Health Service, U. S. Department of Health, Education and Welfare.]
Better than Energy Detector Performance by Human Observers
Authors: Taylor M. M. , Forbes S. M.
Published: November 2005

Observers detected, monaurally, a burst of band-limited noise masked by an independently generated, continuously presented, wide-band noise. An unmasked burst of noise in the other ear served as a cue. Four cue conditions and several signal bandwidths were used. The cue noise burst had the same nominal spectrum, amplitude, and timing as the signal burst, and occurred in each of the two intervals of a 2AFC trial. The four cue conditions were: no cue (O); independently generated cue burst (I); cue identical to the signal (S); cue derived from the signal passed through a wideband 90° phase shifter (X). Potentially, I provides timing information, X supplies information about short-term fluctuations of signal spectrum and amplitude, and S gives complete information about the signal waveform. At all signal bandwidths, the use of O and I resulted in performance levels slightly worse than an energy detector; X allowed much better performance. Results with S approached that of the (2E/N0)12 detector, which at large signal bandwidths is as much as 18 dB better than an energy detector.
Measures of Performance Sensitivity
Authors: Wilcox Gordon W.
Published: November 2005

Several writers have suggested fitting straight lines on double-probability paper to the empirically obtained receiver-operating-characteristic (ROC) curves for human observers. A simple theorem is proved which shows that in acoustical tests in which a fixed signal is presented, no observer of any kind can have a straight-line ROC with other than unity slope. This negative result suggests that some commonly used measures of performance sensitivity are inadequate. A new interpretation of Green's theorem relating the area under the single-interval ROC to the probability of correct response in two-interval forced-choice tasks is given. The interpretation permits a new and direct estimate of the area under the ROC curve in single-interval rating tasks. The estimator, denoted PA, (i) is unbiased, (ii) depends only upon obtained ROC points (i.e., no curve must be fitted to the data), and (iii) generalizes to certain multiple signal-alternative situations. It is further shown that PA is a special case of a more general measure of association between the performance of any two observers (human or electronic) in the same task. As such, it may be used in testing alternative models of sensory processing [This research was conducted at the Sensory Intelligence Laboratory, University of Michigan, and supported by a contract with NASA.]
Statistical Estimation of Parameters of Decision-Theory Models
Authors: Abrahamson Innis , Levitt Harry , Landgraf Lorinda
Published: November 2005

Statistical procedures have been developed for estimating the parameters of decision-theory models. The problem reduces essentially to that of fitting receiver-operating-characteristic (ROC) curves to experimental data. Difficulties arise in that both coordinates of each plotted point are subject to errors of estimation. It is assumed that the likelihood distributions for noise alone and for signal plus noise belong to the same location-scale family (e.g., both normal) with standard deviations σ and σS, respectively. It is further assumed that the samples are sufficiently large to warrant a normal approximation to the multinomial distribution. The analysis has been carried out for YES-NO, forced-choice and rating-scale data, both for σ = σS and σ ≠ σS. Bias and precision of estimation have been considered as well as procedures for testing the underlying assumptions of the model. A Monte Carlo study has been carried ont to investigate the quality of large sample procedures based on the method of maximum likelihood and to compare them with several simplified approximate procedures.
Acoustic Field Due to a Partially Excited Spherical Radiator
Authors: Miller K. L. , Molloy C. T.
Published: November 2005

In previous papers, it was shown how to obtain prescribed acoustic pressure fields by properly choosing the radial velocity distribution on the surface of a spherical transducer. In all of these cases, the transducer was required to radiate from its entire surface. In the present paper the effects of allowing the transducer to be activated only over a portion of its surface is investigated. A desired directivity pattern of the Chebyshev type is selected. The transducer velocity distribution that will produce it is then calculated. This distribution, which is symmetric about the transducer axis, and covers the whole sphere (0⩽θ⩽π) is then successively truncated so that a sequence of velocity distributions is produced each of which is identical with the original distribution up to some angle (θn,) and is zero for θ>θn. The directivity patterns associated with each of these truncated distributions was calculated. The results to date indicate that the Chebyshev-type distribution permits substantial velocity distribution truncation without serious degradation of the directivity pattern. Several numerical examples will be presented. Some results obtained by truncating distributions of the cosnθ type will also be presented.
Propagation of Acoustic Transients in a Fluid Layer
Authors: Coppens Alan B.
Published: November 2005

Approximate solutions of the wave equation have been obtained for some acoustic transients propagated radially outward from a cylindrical source of radius a in a fluid-layer with pressure-release (or rigid) surfaces. The earliest portions of the received signals display amplitude- and phase-modulations dependent on the ratio ωca/c, where ωc is the (angular) cutoff frequency for the excited mode and c is the free-field speed of propagation of sound in the fluid. Relations between this problem and (a) propagation of an acoustic transient from a point source in a fluid layer and (b) propagation of a transient in a duct of uniform cross section are pointed out. [Supported in part by Ship Systems Command and Air Systems Command.]
Finite Amplitude Distortion of 150-kHz Acoustic Waves in Water
Authors: Browning David G. , Mellen Robert H.
Published: November 2005

Second-order acoustic theory holds that a plane sinusoidal pressure wave becomes sawtooth in shape as it propagates. Experiments showing the progressive distortion of a 150 kHz sine wave radiated from a square (40×40 cm) transducer are described. With an initial peak pressure of approximately 1 atm, the distortion becomes highly developed in a 10-m water path. However, the waveform appears to differ slightly from theory.
Masking of Crosstalk by Speech and Noise
Authors: Sen Tapas K.
Published: November 2005

Thirty subjects took part in two laboratory experiments designed to measure detectability and intelligibility thresholds of crosstalk (a portion of speech energy that occasionally gets transferred from one channel to another channel during telephone transmission). Experiment I involved masking of crosstalk by white noise. Experiment II involved masking of crosstalk by white noise and also primary speech. Simulated telephone conversations were used as primary speech. Short sentences were used as crosstalk. In Expt. II, ratings of transmission quality also were obtained. The threshold versus noise functions were found to be linear for high-noise conditions (4-dB pressure spectrum level and higher) and markedly nonlinear for lower noise values. Intelligibility thresholds were found to be 8–10 dB higher than corresponding detectability thresholds. Also, thresholds obtained with both background noise and speech (Expt. II) were found to be higher by 8–10 dB than comparable thresholds obtained with background noise only (Expt. I). The rating data showed that transmission quality was determined largely by the primary speech volume and noise in the circuit, depending very little on crosstalk.
Further Studies of the Intelligibility of Alternated Speech
Authors: Hughes George W. , House Arthur S. , Goldstein David P. , Rupf John A.
Published: November 2005

Previous studies in which subjects were asked to repeat (i.e., shadow) speech that was switched alternately between the two ears have presented evidence that the perception of alternated speech is adversely effected when alternation is synchronous with syllables [A. W. F. Huggins, J. Acoust. Soc. Am. 36, 1055–1064 0964); G. W. Hughes et el., J. Acoust. Soc. Am. 40, 1283 (1966)]. In this study, we compare the perceptual effects of syllable-synchronous switching to those caused by alternation that occurs periodically at the average syllable rate. We also compare effects of alternation at phoneme boundaries with the effects of other conditions of alternation. No striking difference in shadowing performance between the syllable- or phoneme-locked alternation and the periodic alternation were observed, but a strong patterning of errors relative to position in the script was found for all modes of alternation. Our results indicate that script composition may be a more important factor than mode of alternation in determining shadowing behavior. [This work was supported in part by the Air Force Cambridge Research Laboratories under contract.]
Speech Intelligibility as a Function of Helium-Oxygen Breathing Mixture and Ambient Pressure
Authors: Hollien Harry , Thompson Carl L.
Published: November 2005

Speech intelligibility was obtained on Navy divers at sea level (in air) and at 200 and 450 ft (simulated) in helium-oxygen breathing mixtures. Subjects were personnel in training for Sealab 3 at the Experimental Diving Unit, Washington Navy Yard. A total of 26 subjects were evaluated (11 at 0 and 200 ft, 11 at 0 and 0,50 ft and four at 0, 200, and 450 ft). The speech material used was the PB-25 word lists equated by Campbell for difficulty; the lists were read prior to descending and immediately upon reaching depth. The helium-nitrogen-oxygen mixtures were 79/17/4 at 200 ft and 90/8/2 at 450 ft. A relatively nonreverberent recording environment was provided by an enclosure fabricated from mattresses available in the chamber's sleeping compartment. Listeners were 15 University of Florida students trained for tasks of this nature. The combined efforts of HeO2 mixtures and high ambient pressures were extremely detrimental to speech intelligibility (scores of less than 20% were common at 450 ft). [The project was supported by the Office of Naval Research.]
Influence of Bandwidth and Reverberation Time upon Preference Evaluation of Speech
Authors: Sessler G. M. , West J. E.
Published: November 2005

The subjective influence of bandwidth, center frequency, reverberation time and amplitude and delay of early echoes on speech was studied. Selected sentences spoken by different talkers were recorded in an anechoic chamber by a broad-band system. These sentences were reverberated on a digital computer with reverberation processes corresponding to T60 = 0 to 0.5 sec but having specified early echo structure. After this process, bandpass filtering in half-octave steps with bandwidths of 2–5 oct was applied to the sentences. The test stimuli so generated were presented in paired-comparison tests to a number of subjects. The subjects were asked to select that signal from each pair that they believed to be preferable for communication systems. Evaluation of the subjective results was performed on a digital computer using a factor-analysis program. It was found that of the parameters listed above bandwidth is the single most important one for assessing subjective quality. Also, subjective quality increases in general with decreasing reverberation time. This suggests that, within limits, excessive reverberation can be compensated by an increase in the bandwidth of the transmitted signal.
On Line Analysis of Subjective Preference Data
Authors: Magnuski H. S. , Sessler G. M. , West J. E.
Published: November 2005

The preference data described in the previous abstract was analyzed through use of an on-line graphical display. The Graphic 2 console, consisting of a small computer and associated display processor, was programmed to permit the rotation of a three dimensional space and projection of labeled points in this space onto a two-dimensional surface. The coordinate perpendicular to the display surface was represented by the size of the point. By use of a keyboard connected to the computer, the user can intensify the brightness of selected groups of points for independent study. The method permits quick evaluation of three-dimensional data. The first application of this program was the study of results relating bandwidth and reverberation time to speech quality. Results obtained by this method will be demonstrated.
Vocal-Tract Cross-Sectional-Area Measurements with the Impedance Tube
Authors: Mermelstein P.
Published: November 2005

Theoretical studies indicate that the vocal-tract cross-sectional area can be calculated from the tract impedance measured at the lips. The impedance tube method yields this information by external excitation of the tract through the lips with a broad-band pulse train and analysis of the reflected signal [M. R. Schroeder, J. Acoust. Soc. Am. 41, 1002 (1967)]. Test results for a motor driven constriction moving in a uniform tube, as well as results with one subject executing consonant-vowel articulations are presented. The results are in the form of computer-generated movies where individual frames correspond to independent area determinations from the response to excitation pulses separated in time by 10 msec. The extension of the method to nasal sounds is discussed. Impedance-tube measurements accompanied by simultaneous x-ray cineradiography are expected to determine the as yet imprecisely known transformation between sagittal view tract measurements and the corresponding cross-sectional-area values.
A Statistical Theory of Reverberation
Authors: Middleton David
Published: November 2005

A general analytic theory of reverberation has been constructed for the common cases of a weakly turbulent medium, where surface and volume scattering are represented by collections of independent point scatterers obeying suitable Poisson laws in space [Middleton, IEEE Trans. Inform. Theory (July 1967)]. The scattering portions of each medium are described by characteristic position-dependent stochastic linear and time-varying filters, to which are assigned a hierarchy of basic structures. The result is a combined physical-phenomenological model that uses wave theory to determine the form of typical scattered waves, and ray theory to incorporate them into the governing geometry. The intractably complex scatter boundary conditions are embodied in the statistical filter. Frequency-selective apertures, general geometries, and signals are also incorporated. The theory can readily be extended to include nonzero velocity gradients, absorption, and discrete multipath phenomena. Initial experiments show good to excellent quantitative agreement (Kincaid and Rustay, General Electric Co.), including predicted volume and surface effects and spectral broadening caused by inherent doppler of the scatterers. [Work supported by the Office of Naval Research.]
Reverberation Received by a Hydrophone Separated From an Active Acoustic Source
Authors: Prout James H.
Published: November 2005

Reverberation equations have customarily been derived only for a source and receiver at the same point as in the familiar sonar situation. However, the study of interference between two similar active acoustic systems requires a knowledge of the characteristics of the reverberation received at a point separated from the source. A simplified expression for volume reverberation is derived for directional projectors oriented in the same direction but displaced along the beam axis. Reverberation decay curves are presented with source-to-receiver separation as a parameter. The variation of the volume reverberation index, Jv (usually considered a constant), is also discussed.
Volume Scatterring at 3 kHz and 12 kHz off Southern California
Authors: Batzler W. E. , Vent R. J.
Published: November 2005

Directional sound sources aimed vertically downward and using pulses of 25 and 50 msec duration at 3 and 12 kHz were used to obtain volume scattering information in a 2000-fathom area about 200 miles southwest of San Diego. Results during a two-day period expressed as average scattering strength for a water column of unit cross section show −77±2 dB at 3 kHz and −72±2 dB at 12 kHz. Prominent scattering layers were measured at both frequencies during the daylight hours; that at 3 kHz maintained position and strength throughout the night while the 12-kHz layer moved toward the surface at night. These tests of December 1964 tend to agree with similar data obtained in March, November, and July, and with earlier data off Southern California at 18 and 24 kHz. Near-surface scattering was not measured during the 1964 tests, but recent nighttime tests at 3 kHz show high levels near the surface. Scattering levels in this region of high organic productivity are higher than in most of the 50 or more other areas sampled in the Eastern and Western North Pacific.
Relationship between Deep-Water Ambient Noise and Local Wind Field Fluctuations
Authors: Huff Lloyd C.
Published: November 2005

The results of two comprehensive independent investigations on ambient noise and wind field fluctuations versus wind speed are combined to postulate an interconnection between deep water ambient noise and the short term fluctuations about the local mean wind field. The model considers the air/sea interface to be a time changing acoustic impedance and that energy is extracted from the wind field via a turbulent boundary layer. The combined results indicate that for frequencies above 446 cps, the sound pressure level in dB is linearly related to 20 log of the short-term speed fluctuations, and that for lower frequencies down to 112 cps, the SPL approaches this relationship for mean wind speeds above 22 knots. This model affords a reasonable explanation for the observed fact that at high wind speeds, the level of ambient noise is less sensitive to changes in wind speed. Data that represent a direct evaluation of the postulate that ambient noise is physically linked to the kinetic energy of the local wind-speed fluctuations will be presented.
Free Vibrations of Thin Orthotropic Oblate Spheroidal Shells
Authors: Penzes Leslie E.
Published: November 2005

The problem of the free vibrations of a thin orthotropic, oblate spheroidal shell has been solved by the assumptions of orthotropic membrane theory and harmonic axisymmetric motion. The theory has reduced the differential equations of motion to a single ordinary second-order differential equation with variable coefficients. The resulting eigenvalue problem is solved by Galerkin's method. The principal directions of the elastic compliances are assumed to be along parallels of latitude and along meridians. Both the oblate spheroidal and spherical shells were studied by varying the orthotropic constants. The existence of finite bounds for the corresponding mode shapes has been shown. Special consideration is given to the isotropic shell as a limiting case of the orthotropic problem. The present theory in the isotropic case yields to the author's previously published results for the isotropic oblate spheroidal shell as well as the well-known exact solution of the isotropic spherical shell.
Shape Factors in Low-Frequency Noise Reduction
Authors: Bailey J. Ronald , Hart Franklin D.
Published: November 2005

An analysis is made of noise reduction of small enclosures in the low-frequency range where both panel and volume are stiffness controlled. The strong dependence on geometry of the compliance of flexible panels defined in terms of volume displacement and internal-external pressure difference is illustrated. Shape factors for low-frequency noise reduction are established through expressions for the acoustic compliance of enclosures and the compliances of rectangular, circular, cylindrical, and spherical panels, and a comparison of the noise reduction of enclosures involving these elements that have equal volume, panel thickness, and exposed surface area. It is observed that the stiffer, membrane-controlled spherical and cylindrical enclosures have greater noise reduction than enclosures having flexure-controlled flat panels. A companion experimental investigation is described and the results are discussed and compared with the theory. [Work supported by NASA.]
Additive Property of Modal Density for a Composite Structure
Authors: Hart F. D. , Desai V. D.
Published: November 2005

It has been postulated that the modal density for a composite structure is equivalent to sum of the modal densities of the idealized substructures. A demonstration of the validity of this postulate for a particular composite is given by analyzing a structure consisting of two beams joined at right angles to form an L-shaped frame. The frequency equation for the composite and its asymptotic representation are utilized to determine the cumulative number of modes for the structure as a function of frequency. Modal density is determined from a graphical presentation of these results and compared with the sum of the modal densities of the two substructures. Consistent agreement is obtained for all frequencies giving rise to the additive property of modal density for the structure analyzed. [Work supported by NASA.]