bluuebunny/crossref_metadata_2025 huggingface dataset:
Improving Naturalness and Intelligibility of Helium Speech, Using Vocoder Techniques
Authors: Golden Roger M.
Published: September 2005

Previous analysis of helium speech has shown that the peculiar characteristic of this speech is due primarily to changes in formant frequencies of the speaker. Even though some change does take place in the fundamental pitch frequency of the speaker, this effect is small and usually can be neglected. Computation of the resonant frequencies of the vocal tract as a function of the gas mixture occupying the tract gives a reasonable estimate of the changes that take place in the formant frequencies. A modified self-excited channel vocoder was designed to restore approximately the normal values of the talker's formant frequencies while preserving his fundamental pitch frequency. This “formant-restoring-vocoder” (FRV) separates the spectral energy of the helium speech into a number of narrow bands that then amplitude-modulate lower-frequency pitch harmonics derived directly from the hedium speech. The lower-frequency harmonics are separated by bandpass filters that are proportionately narrower and lower in frequency than the spectral-energy separating filters. Helium speech from SEALAB II was processed by an FRV simulated on a digital computer. Results of several simulations indicated that considerable improvement in naturalness and intelligibility of helium speech can be achieved.
Baseband Excitation of the Formant Vocoder
Authors: Campanella S. J.
Published: September 2005

This paper presents the results of recent experiments into the baseband excitation of the formant vocoder for use at data rates of 2400 and 4800 bit/sec. Among the various techniques that have been considered are the use of 1-, 2-, and 3-bit amplitude sampling of the voice-excitation baseband from 200 to 700 cps at rates compatible with the fulfillment of the total-data-rate objectives of 2400 and 4800 bit/sec, respectively. The paper is accompanied by tape recordings of system performance at the above data rates and sampling conditions.
Intelligibility versus Number of Transmitted Spectral Parameters in a Laguerre Autocorrelation Vocoder
Authors: Howard C. R. , Manley Harold J.
Published: September 2005

In this paper, an experiment is described in which articulation scores were measured as the number of transmitted spectral parameters was varied from 6 to 16 in a Laguerre autocorrelation vocoder. The transmitted spectral parameters were the expansion coefficients of the short-time-averaged speech autocorrelation function in terms of Laguerre functions. Thus, these parameters are the same as the expansion coefficients of the speech power spectrum in terms of the Fourier cosine transforms of the Laguerre functions. The analysis and synthesis filters in this vocoder were synthesized from a number of identical RC transistor circuits. The time constant of the Laguerre analysis and synthesis filters was 125×10−6 sec. The system was operated in an analog back-to-back mode for these tests. The results presented show that about 16 parameters are required to achieve performance comparable to contemporary filter-bank vocoders. The intelligibility tests were performed by Bolt Beranek and Newman Inc., in early 1965.
Interpretation of the Speech Oscillogram
Authors: Dudley Homer , Aho Everett
Published: September 2005

Due to the dynamic nature of sound, it is difficult to observe speech characteristics quantitatively by ear and make precise reproducible measurements unless of a rather coarse nature. However, we can stop the motion and obtain static measurable elements by taking pictures of the sound waves. If the picture is a spectrogram, there is an innate distortion that blurs many details, but if the picture is a high-quality oscillogram, then we can make precise reproducible measurements at great length. The visible display contains all the detail that can be heard in the original sound and actually much more. Any speech characteristic that we can hear now becomes visually observable and measurable. The chief application discussed is in the broad field of phonemic analysis. Some other areas of application are mentioned briefly. Consideration is also given to observing on a syllabic-message basis rather than the usual carrier-wave basis so as to reduce the amount of superficial or unnecessary information considered and to speed up the interpretation of the speech waves.
Voiceprint Classification for an Extended Population
Authors: Kersta L. G.
Published: September 2005

The binary-code automated classification system for Voiceprints previously described for a 12-member population has been extended to a 120 member population [Voiceprint classification, J. Acoust. Soc. Am. 37, 1217(A) (1965)]. The classification system is based upon the uniqueness of a selected quantized amplitude, frequency vs time matrix. Experimental data indicate unique speaker selection of better than 90 per cent for the tested population. When the classification is based serially on five selected cue words and subgrouping the selection accuracy is improved. The goal sought was for a method, preferably automated, by which the population in which a subjective search must be made for unique identification could be reduced. This has been accomplished. An automated identification method equating that of trained subjects has not yet been achieved. The major part of the work reported here was done at the Bell Telephone Laboratories.
ALTEXT: A Multipurpose Processing Language
Authors: Stark R.
Published: September 2005

ALTEXT, a multipurpose programming language has been used extensively at Lockheed Missiles and Space Company for linguistic research and for processing textual data: for example, the conversion of orthographic form of words into corresponding phonetic forms and the formatting of the phonetic data according to source dictionary and to regional dialects [B. V. Bhimani and R. Mitchell, J. Acoust. Soc. Am. 38, 934(A) (1965)], correlation studies, etc. In processing dictionary entries, an ALTEXT program required 18 min to process over 73 000 words for which the rate of processing was 8000 words/h with a COMIT program. A program that processed 2000 records with SNOBOL in 70 min was written in ALTEXT and the operating rate was increased to 10 000 records in 3.62 min. The speed of ALTEXT is a result of efficient input-output and of coding that is similar to that in assembly languages. Statements in ALTEXT consist of self-descriptive English words and algebraic expressions that resemble those in FORTRAN, making it an easy language to learn. [Work supported by Lockheed Independent Research.]
Optimal Computer Programs for Monosyllabic English Words
Authors: Bhimani B. V. , Mitchell R.
Published: September 2005

Detailed discussion of the performance of company programs that generate the phonetic transcriptions of lexed items monosyllabic according to the Shorter Oxford Dictionary for each of five distinct sets of transcriptions is given in this paper. [B. V. Bhimani and R. Mitchell, J. Acoust. Soc. Am. 38, 934(A) (1965).] Programs that are “optimal” in the sense that they yield transcriptions from the orthographic forms of lexed items for each dialect recognized by each of the five sources, without regard to actual citations by the authorities, have been written. Programs that are ldquo;optimal” in the sense that they yield transcriptions for at least one of the recognized dialects in each of the five sources have also been prepared. A program has also been written that is optimal in the sense that it generates the transcriptions of lexed items for at least one of the dialects in all five sources at once. Comparative analysis of both the performance and the results of these computer programs is given. [Work supported by Lockheed Independent Research.]
Underwater-Sound Scattering from an Irregular Surface
Authors: Mitchell S. K. , Osborne W. H. , Barnard G. R.
Published: September 2005

The scattered field of underwater sound from a randomly irregular surface has been measured under laboratory conditions. A 85×85-cm surface was accurately modeled from expanded polystyrene. From 4225 sample points, it was determined that the surface had a relief of 5 cm, a height of 0.925 cm, and a root-meansquare slope of 0.22. The sound sources were piston transducers with 8° beam widths at the half-power points driven at frequencies of 100 and 200 kHz, which corresponds to acoustic wavelengths of 1.5 and 0.75 cm, respectively. Calculations of the scattered field were made with a formula de6rived from the Helmholtz theorem. Terms in the integral involving surface heights were statistically represented. This approach was outlined by C. Eckart but was developed by T. G. Muir for a linear autocorrelation function that characterized this model. The usual approximation that the normal derivative of the scattered field on the boundary equals that of the incident plane wave is not valid for this surface, even for the cases of no shadowing. It was found that an alternate assumption, that the normal derivative of the scattered field be zero on the surface, leads to results that are in better agreement with the experimental measurements. [Work sponsored by the U. S. Navy Bureau of Ships.]
Model Tank Measurements of the Coherence of Underwater Acoustic Signals Reflected from Plates and Cylinders
Authors: Aukward J. A. , Johnson B. L. , Weinstein Marvin S.
Published: September 2005

The spatial coherence of signals reflected from steel plates and cylinders both water- and air-backed was measured for angles of incidence between 6° and 70°. The five plates employed as targets ranged in thickness between 0.006 and 0.074 in. The wall thickness of the 2- and 4-in.-diam cylindrical targets varied between 0.035 and 0.156 in. The spatial coherence of the reflected signals was observed to be essentially constant, approximately 0.9, for all targets over the range of incident angles measured. The coherence of signals transmitted through the plates was also observed as a function of the angle of incidence. For plate thickness ≧ 0.018 in., degradation of the coherence was observed, particularly in the region of the critical angle for the dilatational wave. Correlation was determined by tlle polarity-coincidence method, using a wide-band noise transducer, approximately 0.6–1.2 Mcps, as signal source. [Work supported by the Bureau of Weapons, U. S. Department of the Navy.]
Results of Volume-Reverberation Tests
Authors: Keane John J.
Published: September 2005

Reverberation tests were conducted as part of an over-all NAVAIRDEVCEN program for improving both sonar systems and the capability for predicting system effectiveness. A 15.4-kHz sound source was used to investigate volume reverberation levels as a function of source level, pulse length, and FM sweep width. Explosive sound sources were used to investigate diurnal variation and the spectral distribution of reverberation levels. The data show that the relationship between volume-reverberation level and source level is linear. An equation is empirically derived that expresses a less-than-linear dependence of volume reverberation levels on pulse length. The amplitudes of the deviations from the mean levels are shown to be lower for the FM mode than the sinusoid mode and inversely proportional to the swept bandwidth. The mean levels, however, exhibit no significant differences. Nighttime reverberation levels for the systems used are shown to be significantly higher than daytime levels.
Analytical Study of Underwater Acoustic Backscatter
Authors: LeBlanc Lester R. , Hill R. F.
Published: September 2005

A mathematical model of the scattering of underwater acoustic energy from the surface has been derived that considers the surface to be composed of differential facets with dipole beam patterns [J. Acoust. Soc. Am. 37, 1191(A) (1964)]. The autocorrelation of the received signal is obtained by statistical analysis of the individual facet-related signals and is shown to be related to the spatial correlation and the mean-squared magnitude of the surface as well as the transducer characteristics and incident angle. This backscatter autocorrelation function is utilized to obtain average backscattered power curves and backscattered power spectra. The analytical results compare favorably with model-tank experiments. [Work supported by the U. S. Office of Naval Research at the University of Rhode Island.]
Reverberation from the Ocean Surface
Authors: Brown J. R. , Scrimger J. A. , Turner R.
Published: September 2005

Measurements of surface reverberation made in the North East Pacific are presented. Sounds produced by 1-lb explosive charges detonated at depths between 175 and 1000 ft yielded scattering strength results in the frequency range 320–10 240 cps, and between grazing angles of 2° and 75°. The scattering-strength values are generally lower than those reported in the literature. Although the range of wind speeds over which the data were gathered was not great, a wind-speed dependence is indicated, as is a frequency dependence. A program of surface-wave measurement in conjunction with surface-reverberation measurement has been initiated in an effort to resolve the variation in the results obtained by different investigators.
Compressional Sound Velocity in Marine Sediments
Authors: Duykers L. R. B.
Published: September 2005

Shumway [Geophysics (1960)] found agreement between laboratory measurements in unconsolidated marine sediments by a resonance technique and values calculated from a formula, assuming the rigidity to be proportional to the volume fraction of sand grains. The same formula applied to deep-sea sediments fails to agree with laboratory measurements, using the same resonance technique. The failure seems to be due to pressure effects. Values calculated from a new formula, assuming the rigidity to be a product of both the pressure and the volume fraction of sand grains, seem to agree with the measurements. In addition, a simplified formula is proposed that allows the sound velocity to be calculated to a reasonable approximation from the in situ bulk density, the compressibility of sea water, the porosity, and the depth.
Experimental Investigation on the Reflective Characteristics of a Deep Ocean Bottom
Authors: Karmargin Michael C.
Published: September 2005

The frequency dependence of reflectivity from a deep ocean bottom is investigated over a frequency range 100–3000 cps at several angles of incidence. Both explosives and pulsed single-frequency projectors are utilized as sources for illuminating the ocean bottom. The absolute magnitude of the transfer function representing the bottom is approximated from a measure of reflected levels from both source types. The results are interpreted in the light of the presence of thin layers in the sediment, bottom roughness, and the frequency dependence of attenuation in the bottom.
Ultrasonic Investigation of Ion Association in Solution
Authors: Atkinson Gordon
Published: September 2005

Understanding ion association is a necessary prerequisite for an understanding of electrolyte solutions. It is important not only to solution chemistry but also to such diverse fields as oceanography, polymer chemistry, and biochemistry. Unfortunately, classical-solution techniques such as conductance have proven inadequate based as they are on a continuum-solvent model. The introduction of relaxation techniques and, in particular, ultrasonic absorption has provided an extremely powerful approach for the resolution of this problem. We describe recent results in this laboratory, obtained by conventional transmitted-pulse ultrasonic measurements in the range 2–300 MHz. A general model for ion association is presented, based on extensive work in aqueous MnSO4, MgSO4, and CoSO4 solutions. The model is extended to recent data on 1-1 salt association in nonaqueous solvents. Finally an analysis is given of the association of some lanthanide sulfates in water. An attempt is made to identify the important parameters that govern the thermodynamics and kinetics of ion association in a molecular solvent.
Ultrasonic Relaxational Behavior of Biological Macromolecules
Authors: Edmonds Peter D.
Published: September 2005

Possible relaxation mechanisms are considered that may account for the observed interactions of low-amplitude ultrasound with macromolecules in dilute aqueous solution and also in high concentration. Such studies are relevant to the kinetics of association and dissociation of hydrated macromolecules in the former case and of ordered liquid structures, such as membrances, in the latter case. [Work supported by grants from the National Institute of General Medical Sciences, National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare, and the National Science Foundation.]
Ultrasonic Vibration Potentials in Polyelectrolytes
Authors: Zana Raoul , Yeager Ernest
Published: September 2005

The propagation of ultrasonic waves through a solution of a polyelectrolyte gives rise to ac potentials of the order of 10−5 V per unit velocity amplitude (1 cm/sec). The magnitude depends on the mechanical and electrical properties of the charged polymer ions and the other ionic constituents. Although a theoretical description is still lacking, polyelectrolyte vibration potentials appear capable of providing interesting information concerning these propperties and the interaction of other ionic constituents with the polyelectrolyte. Studies of this effect have been carried out with pulse-modulated ultrasonic waves at 200 kcps with a double platinum-probe assembly for measuring the ac potentials. With polyelectrolytes such as poly-L-glutamic acid, substantial changes in the magnitude of the effect have been observed with increasing pH due to a change in configuration (helix-coil transition). Other polyelectrolytes exhibiting a random-coil configuration (e.g., polyacrylic acid) also have been studied and the dependence of the effect on such parameters as type and concentration of other ions and degree of neutralization established. [Research supported by the U. S. Office of Naval Research.]
Chemical Reactions Caused by Ultrasound Waves in Liquids
Authors: Weissler Alfred
Published: September 2005

Chemical reactions caused by ultrasound waves in liquids are surveyed, with some attention to recent research abroad, such as that in the USSR. Consideration is given to the mechanism of the effects and the importance of the nature of the dissolved gas. Hemoglobin, amino acids, enzymes, and other biochemical molecules are included in the discussion. Sonochemistry in nonaqueous systems, a new area, is also described briefly.
Sonolysis of Coal Derivatives
Authors: Kessler Theodore , Sharkey A. G. , Friedel R. A.
Published: September 2005

The purpose of this investigation was to determine what new organic compounds or high concentration of a particular organic species can be formed by exposure of coal derivatives to ultrasonic energy. Tetralin, 1-methylnaphthalene, and pyridine were used as model compounds. Gaseous and solid reaction products resulting from the ultrasonic irradiation of the above coal derivatives were determined, using mass spectrometry. Products from the irradiation of tetralin were studied as a function of time, atmosphere, and sample size. The sonolysis of tetralin produced C2H2, HCN, CH4, H2, CO, and CO2, depending upon the experimental conditions. The cleavage of organic liquids by ultrasonic cavitation in the absence of water, recently reported by Weissler, Pecht, and Anbar, was also observed in this study.
Noncavitating Ultrasonic Irradiation of Enzyme Solutions
Authors: Macleod R. M. , Dunn Floyd
Published: September 2005

The inactivation of enzyme solutions by cavitating ultrasound has been reported previously. Whether cavitation is necessary to cause inactivation of enzymes in solution is an important question to those seeking an explanation for the effects of noncavitating ultrasound on tissues, and hence it is the subject of this investigation. Five enzymes (α-chymotrypsin, ribonuclease, trypsin, aldolase, and lactate dehydrogenase) were irradiated with noncavitating ultrasound under a variety of conditions. Frequencies were in the range of 1 to 30 Mcps, intensities ranged between 0.5 to 500 W/cm2, depending on the frequency, and irradiation times were between 0.1 to 600 sec, depending on the intensity. The temperature, pH, and concentration of the solutions depended on the properties of the enzyme being studied and where appropriate, these variables were altered to determine if they affected the results of irradiation. Analytical procedures employed included measurements of enzyme activity, specific rotation, ultraviolet absorption spectrum and sedimentation coefficient. Qualitative information was provided by chromatograpbic analysis. The results of these analyses indicate that noncavitating ultrasound has no effect on enzyme solutions in vitro. [Work supported by the U. S. Office of Naval Research Acoustics Branch, and the National Science Foundation.]
Changes Brought about at Surfaces by Small-Scale Acoustic Streaming
Authors: Nyborg Wesley L. , Packard R. E. , Parsons D. H.
Published: September 2005

Acoustic streaming generated at interphase boundaries is characterized by modest speeds but high-velocity gradients near these boundaries. Because of its small-scale characteristics, and also because it can be pulsed in time (by pulsing the sound source), such “microstreaming” offers unique possibilities for applying stresses or bringing about convection at surfaces. The stresses so produced are capable of removing weakly adhering surface layers or, in the case of films continuously formed (such as oxide layers in passivation of iron), of affecting their formation. Order-of-magnitude estimates, based on available data on surface self-diffusion coefficients, indicate that the stresses should cause migration of surface atoms on solids at temperatures just below those for melting. Through its effects on surface structures, as well as by convective action, microstreaming causes changes in potentials and/or current at electrodes, as well as in reaction rates. In this paper, recent results are presented on surface stresses caused by microstreaming, and on effects of microstreaming on surface reactions. [Work supported in part by the U. S. Air Force Office of Scientific Research.]
Theories of Musical Structure as a Source for Problems in Psychoacoustical Research
Authors: Randall J. K.
Published: September 2005

Electronic media have opened two paths that research into the perception of musical sound is now following: the first is a path toward answers to traditional psychoacoustical questions, and the second is a path toward exposing more fully the musical misconceptions that may lie at the root of these questions. The purpose of this paper is to explore the second of these paths. In order to cast doubt on the idea that psychoacoustical research is, in fact, independent of any theory of musical structure, the argument proceeds from an elaboration of the familiar premise that the “perceived characteristics” of a musical sound are enmeshed in and partly determined by a perceived or imagined musical context to the suggestion that such research is on occasion handicapped by the parochial nature of those particular theories of musical structure upon which it knowingly or unknowingly tends to rely. Tapes produced at Princeton's Music IV facility are offered in evidence.
Some Notes on Computer-Generated Music
Authors: Roberts Arthur
Published: September 2005

Continued use of MUSIC4F, a FORTRAN version of the Bell Telephone Laboratories music-generating program “Music IV” has occasioned observations onu the nature of the sounds produced and their utility as “instruments” in extended music compositions. The quality disparagingly called “electronic” by musicians appears to be owing, at least in part, to the linear-amplitude characteristics of the sound generators, in contrast to the nonlinear characteristics of conventional instruments. Consequently, the listener cannot distinguish the original-instrument loudness level as distinct from the reproduction level. The program requires excessive computer time in certain cases, notably for the generation of aperiodic but nonrandom waveforms. The computer-performer interface characteristics are a major drawback to rapid mastery of the computer regarded as a musical instrument, being notably inferior even to those of the electronic-analog sound-generating devices. The use of small computers, or time-shared larger ones, and special simplified on-line music-generating programs offers a significant improvement.
Frequency-Selective Detection of Signals in Noise
Authors: Greenberg Gordon Z. , Larkin W. D.
Published: September 2005

A probe-signal method was developed and used to study differential detection as a function of the signal frequency when observers were instructed to listen for signals of a single fixed frequency. All signals were presented in a continuous background of noise, with a two-alternative temporal forced-choice procedure. Response characteristics were found that are consistent with the idea of an underlying frequency-selective mechanism similar to a fairly narrow bandpass filter. A discussion is given of various applications of the method to produce data that will identify the strategies that an observer uses to process certain auditory stimuli selectively. [Work supported by the National Institute of Neurological Diseases and Blindness, National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare.[
Effects on Detectability of Frequency Variation during an Observation Interval
Authors: Hafter Ervin R. , Henderson Donald , Bourbon Walter T.
Published: September 2005

In many cases, observers are highly sensitive to variations in a stimulus parameter. In order to ascertain whether this sensitivity to change would increase the detectability of such a stimulus, noise-masked detection was measured for equal-duration, equal-intensity signals, some of which were held at a constant frequency and some of which were varied in frequency during the observation interval. The continuous signals were gated sinusoids of 250, 450, 950, 1750, 2550, and 3550 Hz; the frequency-varying signals were linear FM slides centered at the frequencies of the fixed tones and with a bandwidth of 100 Hz. A second category of frequency-varying signals included “housetop” FM slides that covered the 100-Hz bandwidth in half the duration of the first slides and then linearly returned to the starting frequency in the second half of the signal duration. Thus, they exhibited the same frequency, bandwidth, and intensity, but twice the rate of change in frequency. The noise was wide-band, Gaussian. The single frequency signals were more detectable than the linear FM slides, which were more detectable than the housetop FM slides.
Replication and Revisions of Egan's Method of Free Response
Authors: Watson Charles S. , Nichols Thomas L.
Published: September 2005

Listener performance was measured under several condittions similar to that described by Egan as the “Method of Free Response” [J. Acoust. Soc. Am. 33, 993–1007 (1961)]. In addition to randomly spacing 10 signals of low detectability, 150 msec in duration, 500 Hz, within each 5-min listening period, 10 “noise-alone intervals” were also defined in each period. The latencies of first responses were measured, timed from the onset of each observation interval. Distributions of these response latencies were separately constructed for signal-plus-noise and for noise-alone intervals. Indices of detectability calculated from these distributions support Egan's conclusions that (a) signal strength must be increased by approximately 2 dB when observation intervals are not defined for the listener, if he is to maintain his performance at the level achieved with defined intervals, and (b) this decrement in performance is largely a function of uncertainty about the exact instant of signal occurrence, and not of the sparcity of signals. [Work sponsored by a grant from the National Aeronautics and Space Administration to the Defense Research Laboratory.]
Correlations of Auditory and Visual Signal-Detection Parameters
Authors: Gunn Walter J. , Loeb M.
Published: September 2005

It was hypothesized that individuals adopt characteristic criteria for responding to signals and that criteria for responding should correlate when signals are presented through different sensory channels. In the present experiment, 20 subjects were to detect auditory signals (40, 0.5-see pulses of white noise 1.8 dB more intense than 200 other pulses in a train), or in a different session, visual signals (40, 0.5-see pulses of light 3 dB more intense than 200 other pulses in a train). Interstimulus interval was 2 sec; position of the signal pulses within the train was randomly determined. Detections and false responses were scored for each subject and β and d′ computed. Moderately large and statistically significant correlations between modalities were observed not only for β but also d′; i.e., not only does there appear to be a characteristic attitude toward criterion for responding that is common to the auditory and visual moralities, but apparently, there is also some mechanism that determines differential sensitivity that is common to the two modalities.
Testing for Sequential Dependencies
Authors: Levitt H.
Published: September 2005

Some psychophysical procedures assume that successive judgments are statistically independent. A method for testing the validity of this assumption using the up-and-down procedure is described. Two identical up-and-down strategies are run concurrently. Observations for each strategy are interleaved according to a rule designed to produce a large difference between the resulting estimates should a sequential dependency exist. The null hypothesis is postulated that no dependency exists, and the two estimates are compared for differences significantly larger than could have occurred by chance. The experiment reported here was designed to test for the possibility that responses of the same type are more likely to follow in sequence than would occur with statistically independent judgments (i.e., all factors being equal, the probability of ++ or −− greater than the probability of +− or −+). The threshold for a 250-cps tone in wideband noise was measured for five subjects on three separate occasions. Two of the five subjects showed a small, but consistent difference between the two concurrent estimates, indicating a slight tendency for like responses to follow in sequence.
Modest Computer-Controlled Psychoacoustical Facility
Authors: Pollack Irwin , Headly Peter , Maas Eugene
Published: September 2005

A psychoacoustical facility, built around a small digital computer (Digital PDP-5), is briefly described. In contrast with a previously reported computer-controlled facility [McQuillin et al., J. Acoust. Soc. Am. 34, 1999(A) (1962)], no direct mechanical control of conventional audio generators has been attempted. Instead, the computer is assigned the entire task of carrying out the psychoacoustical experiment. Stimulus generation is presently confined to trains of monopolar pulses with well-defined temporal properties. Interpulse intervals, generated by programmed “delay loops,” provide for temporal differences as small as 0.75 μsec between successive intervals. Several psychophysical procedures have been employed for efficient experimentation. The implementation of sequential sampling procedures permits termination of the psychophysical experiment when the results meet a previously determined criterion of precision. Sample experiments are illustrated. [Research supported by National Science Foundation.]
Acoustic Wave Produced in a Conical Horn by Stopping a Converging Steady Flow Instantaneously
Authors: Blackstock David T.
Published: September 2005

A rigid, infinite, conical horn containing a converging, steady flow of water is considered. The flow velocity is u=−u0 at the horn throat r=r0. The throat is open to empty the water. At time t=0, the opening is suddenly closed. The abrupt stoppage of the water generates a strong compressional wave, which propagates in the direction of the horn's mouth. A description of the wave, with finite-amplitude effects included, is desired. In the linear approximation, the pressure waveform is headed by a sharp jump of magnitude ρ0C0u0r0/r. The head appears at the point r=r0+c0t and is followed by an exponentially decreasing tail. When finite-amplitude effects are taken into account, it is found that linear theory underestimates the propagation speed of the pulse and overestimates its amplitude. The true magnitude of the pressure jump is the small-signal value multiplied by the factor 2/[1+(1+2βε ln r/ro)12], where ε=u0c0 and β ≐ 4. Therefore, if attenuation caused by nonlinear effects is to be kept negligible, ε must be chosen small and r0 large. [Work supported by General Dynamics/Electronics, Rochester, N.Y.]
Creeping-Wave Pulses on Circular Cylinders
Authors: McNicholas J. V. , Überall H.
Published: September 2005

Many recent studies of the transient behavior of diffracted waves have been concerned only with the field in the small neighborhood behind the pulse front. Some authors have given the forms of the field of plane pulses far behind the pulse front. The present work was initiated in order to bridge the gap and find the total pulse shape on the cylinder surface. These waves on the cylinder surface are the creeping waves of W. Franz. It is found that, near the front of the pulse, the field builds up slowly and also near the end of the pulse the field falls off slowly; what happens in between, of course, depends upon the type of incident pulse. [Work supported by the David Taylor Model Basin and the U. S. Office of Naval Research.]
Representation of Lightly Damped Transients
Authors: Wiseman W. J. , Wolff S. S.
Published: September 2005

Historically, Fourier techniques have been used extensively for the representation of all types of signals. More recently, Huggins, Young, Sopko, and others have been successful in representing signals on bases of lower dimensionality than Fourier methods would require by matching their basis elements to the signals considered. This paper presents a comparison of the results obtained when certain underwater acoustic signals of a lightly damped, oscillatory nature were represented, using both Fourier techniques and a basis more closely matched to the signals: orthonormalized decaying complex exponentials. It is further shown that improved practical techniques rcsult from considering the signals as envelopes of a sinusoidal carrier. [Work supported in part by the U. S. Office of Naval Research.]
Study of Jet-Engine Noise at Low Exhaust Speeds
Authors: Gordon Colin G.
Published: September 2005

The dependence of the noise output of the jet engine upon the eighth power of the exhaust velocity has been firmly established both theoretically and experimentally—at least for the higher subsonic speeds. The advent of the bypass engine and the continued increase of the bypass ratio of these engines have produced a very considerable reduction in the radiated noise. In some instances, however, the reduction has fallen short of that expected, on the basis of an eighth-power law. It seems probable that other noise sources having a lower velocity exponent now dominate the radiated power. In order to investigate the transition and the nature of these sources, an experimental study using model air jets has been initiated. The effects of both fixed and rotating flow spoilers upon the radiated power have been investigated. Some results of this study are presented in this paper and conclusions drawn regarding the application of these to the real-life problem of predicting and controlling the noise of the modern jet engine. [Work supported by National Aeronautics and Space Administration, Langley Field, Virginia.]
Rôle of Refraction in Jet Noise
Authors: Atvars J. , Schubert L. K. , Grande E. , Ribner H. S.
Published: September 2005

Recent experiments in the UTIAS anechoic chamber have delineated this rôle and appear to prove that outward refraction and diffraction alone account for the marked falloff normally found in jet noise near the axis (e.g., below 40° for turbojets). [Extremely cold jets (−180°C) were found to exhibit an inward refraction or focusing effect that produces a marked lobe of enhanced emission along the jet axis.] The experiments show in addition that the basic jet noise—the noise with refraction and convection effects corrected out—has a polar pattern resembling an ellipse in cross section, rather unlike Lighthill's four-leaf clover. The evidence lies in the comparison of the polar refraction patterns for pure tones injected into a jet (“point” source) with the polar directional patterns of narrow-band filtered jet noise: at each frequency, the corresponding curves match quite well near the jet axis. The basic directivity pattern is deduced by correcting out the refraction via the injected sound curves and the convection by a theoretical factor on which there is substantial agreement. [Work supported by National Research Council (Canada), U. S. Air Force Office of Scientific Research, and National Aeronautics and Space Administration.]
Noise Radiation from Impinging Jet Flows
Authors: Montegani F. , Dosanjh Darshan S.
Published: September 2005

Experimental investigations of the noise from an underexpanded axisymmetric (d=38 in.) main jet flow at 100 psig stagnation pressure interacting with a transversely impinging concentric annular (34-in. diam by 364 in. wide) jet flow have been conducted in an anechoic chamber. The impingement location of the annular flow (within one diameter downstream of the main jet nozzle exit) and percent impingement (here equal to the annular jet stagnation gauge pressure) were varied. Between 0% and 8% impingement, the total acoustic power radiated increased from 142 dB re 10 13 W to 148 dB. Significantly, between 8% and 33% impingement, the power radiated decreased to a relative minimum that occurred between 15% and 25% impingement, depending on the impingement location. This relative minimum was within 2 dB of the power radiated by the main jet flow alone. Spark shadowgraphs of the underexpanded main jet flow and its interaction with annular jet flow revealed interesting changes in the shock pattern. Possible bearing of these changes on the observed behavior of the acoustic power is discussed. [Research sponsored by the National Aeronautics and Space Administration.]
Surface-Pressure Correlation Function for a Cylinder in a Diffuse Reverberant Sound Field
Authors: Wenzel Alan R.
Published: September 2005

A theoretical calculation of the surface-pressure correlation function for a rigid, infinitely long cylinder in a diffuse sound field (i.e., a sound field in which waves having all frequencies impinge on the cylinder from all directions) is given. The analysis includes the effects of scattering of the sound waves by the cylinder. A general expression is derived that gives surface-pressure spatial correlation as a function of both circumferential and longitudinal separation for any arbitrary distribution of sound amplitude versus frequency. With the aid of a computer, numerical results are obtained for the case of a narrow-band acoustic noise. These results show a decrease in spatial correlation with increasing circumferential and longitudinal separation, as well as with increasing frequency. The results also show the characteristic damped oscillatory behavior of the spatial correlation function with increasing spatial separation. [Work supported by NASA-Marshall Space Flight Center, directed through Brown Engineering Company, Huntsville, Alabama.]
Surface-Pressure Fluctuations due to Shock-Turbulence Interaction
Authors: Lowson Martin V.
Published: September 2005

High levels of pressure fluctuation have been observed on surfaces beneath shock waves in turbulent flow. These levels contribute substantially to the buffet loadings experienced by aircraft and space vehicles in transonic and supersonic flight. It has usually been suggested that these fluctuations are associated with an oscillating shock phenomenon. However, it is shown here that the interaction between the turbulence and shock is sufficient to account for the observed fluctuating pressure field. Computations have been performed following the methods of Ribnet (NACA Rept. No. 1233), but explicitly including the nearfield pressure terms. It has been found that, for instance, the interaction of turbulence of intensity 0.05 with a typical separation shock at M=2.0 will generate a near field noise level of 169 dB. The interaction between shocks and sound has also been studied following Moore (NACA Rept. No. 1165). The predicted magnification of incident sound behind the shock (4.5 dB for a M=2.0 separation shock) is probably sufficient to account for the observed “sensitivity of an oscillating shock to wind-tunnel noise.” [Work supported by the National Aeronautics and Space Administration.]
SST Sonic-Boom Evaluation Status
Authors: Thompson J. R.
Published: September 2005

Nearfield sonic-boom theory shows that design modifications can result in reduction of the peak positive overpressure predicted for the critical low supersonic climb régime of an SST. Such modifications, however, may result in performance penalties. In order to perform the indicated tradeoff, values of structural damage potential and human response are needed for the predicted signatures. This paper explores these effects for two candidate SST configurations differing only in area distribution. Generalized structural response envelopes computed by transient time-history methods indicate little difference in response to the different shaped signatures of the two designs even though the peak positive overpressures differ by a factor of about 1.7. In a simulator of the variable volume type, human subjects judged the signatures to be equally loud at the predicted peak overpressure ratio of 1.7. These results imply that the two designs do not differ significantly in structural-damage potential or judged loudness and that peak positive overpressure is not a valid criterion for comparing different shaped signatures. Possible explanations of the results are discussed.
Origin of Subharmonics in the Peripheral Auditory System
Authors: Dallos Peter J. , Linnell Craig O.
Published: September 2005

Undertones were investigated in guinea-pig and chinchilla ears by recording cochlear-microphonic potentials and sound pressure at the eardrum. Two fundamentally different types of subharmonics were demonstrated. The first type, which we have described in the past, appears at one-half the stimulus frequency. This type of undertone was shown to originate as a consequence of the nonlinear vibratory pattern of the eardrum-malleus complex, by recording subharmonics in the sound in front of the eardrum at various stages of destruction of the cochlea and middle-ear structures. The second type of undertone appears in pairs at frequencies that are equally placed above and below one-half of the driving frequency. At threshold only certain frequencies are seen, but above threshold the undertone frequencies can be systematically changed by varying the sound intensity. The hypothesis that these strange undertones originate in the cochlea was tested by bypassing the middle ear in the process of eliciting cochlear microphonics. [Work supported by the National Institutes of Health, U. S. Department of Health, Education, and Welfare.]
Noise Control for Natural-Gas-Engine Installations
Authors: Hoover R. M.
Published: September 2005

Natural-gas engines are being used frequently as an alternative to electric motors to drive refrigeration equipment, and electric generators. These units are being installed not only in new buildings such as motels, office buildings, and apartments, but also in existing buildings to either replace or supplement existing equipment. In all instances, and especially in the latter type of installation, the owner is justifiably concerned about the noise or vibration produced by the gas engine. Data presented in this paper, obtained from several installations, show, however, that adequate noise control can be provided for the gas engine, using reasonable measures. Data are also included to show that, as with most mechanical systems, there are a number of noise sources associated with the typical gasengine installation. These other sources such as fans, cooling towers, and compressors should also be considered when designing noise-control measures for the installation in order to achieve adequate noise control for the complete system.
Design of Aerospace-Oriented Acoustic Facilities
Authors: Dendrinos Steve
Published: September 2005

Present-day aerospace acoustic facilities are outgrowths of the reverberation room-anechoic room pair that has been used for years in architectural acoustics. There are serious difficulties in use of the reverberation rooms and their outgrowths in the simulation of acoustic environments produced by large rocket vehicles. The requirements for present and future acoustic facilities for use in aerospace work are examined. Current facilities are examined for their applicability in meeting these future requirements. Since there are many approaches toward the design of a facility, several design criteria are presented as guidelines toward the development of an acoustic facility that will meet future aerospace requirements.
Attack on tha Number Two
Authors: Ladefoged Peter
Published: September 2005

The Jakobson-Halle description of speech in terms of binary distinctive features is not valid. There are logical inconsistencies if features such as tone and compactness are defined in physical terms. It is impossible to give adequate definitions of features when they are required to be autonomous and relative, and when there are three contrasting linguistic units (such as tones in Yoruba) that differ only in the relative degrees in which they exhibit a particular property (rate of vibration of the vocal cords, or fundamental frequency, or nonlinguistically defined pitch). If the features are not required to be autonomous, the definitions lead to a disguised ternary (or n-ary) system with a hierarchy of features. If recourse is made to definitions in terms of linguistically determined perceptual classes, then the system is trivial and cannot be said to permit phonetic specifiability of linguistic units is accordance with a universal phonetic alphabet. A better view is that phonological descriptions consist of an ordered set of necessary and sufficient statements linking grammatical statements with physical events. This view requires a new phonological theory.
Auditory Search
Authors: Davis Julia
Published: September 2005

Auditory search was examined by measuring responses to syllables embedded in sentences. Sentence length, position of a syllable in a sentence, the grammatical class of the word containing a syllable were variables studied. Observers were required to listen to a sentence followed by a syllable and to determine whether or not that syllable appeared in the sentence. Sentences ranged in length from 15 to 55 syllables. 96 iudividuals served as observers. Accuracy of syllable identification and search time were measured; observers also reported their mode of search. Analysis of variance was employed to assess relevance of variables to auditory search. The results indicated that search involved rehearsal of a sentence, processing of a sentence in units that are probably related to syntactical structure, and was more efficient when time of search was short. Results are discussed relative to theoretical concepts of auditory filtering, chunking, storage, and retrieval.