bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectrographic Study of Vowel Reduction
Authors: Lindblom Björn
Published: November 2005

Our knowledge of the acoustic nature of reduced vowels as found in rapid speech or short syllables appears to be rather limited. It is generally assumed that a vowel that is shortened, e.g., owing to its occurrence in a weakly stressed syllable, tends to approach [ ə ] both articulatorily and perceptually. This paper reports some of the results that have emerged from a spectrographic study of vowel reduction in Swedish. The speech material consisted basically of 24 nonsense words formed by commutation of /ɪ, ɛ, ʏ, œ, a, θ, ɔ, ʊ/ in three consonantal environments /b-b/, /d-d/, and /g-g/. Preliminary experimentation preceded the selection of sentence frames that generated durations of the above vowels within 100–300 msec. The results indicate continuous shifts in formant frequencies as a function of vowel duration. As the vowel grows shorter, this shift, which is most conspicuous in the second formant, takes the form of an increasing displacement away from a hypothetical “bull's-eye” formant frequency and is directed towards the adjacent consonant locus. The magnitude of the displacement seems to be dependent on the distance in frequency between the vowel target and the locus. The results are interpreted as indicative of constraints inherent in the articulatory mechanism.
Vocoder Performance on Voiceless Fricatives
Authors: Karis C. , Howard C. R. , Dolansky L.
Published: November 2005

A series of intelligibility experiments has been conducted, utilizing an 18-channel vocoder-multiplex system. The test material consisted of CVC nonsense syllables containing the fricatives /s/, /∫/, /ɾ/, and /θ/. Listener-test results demonstrated that vocoder performance on these speech samples was poor. The low intelligibility was found to be primarily attributable to erroneous listener responses to prevocalic fricatives. Although classical ambiguities such as /f/-/θ/ confusion were present, there was, in addition, a predominance of voiced-fricative responses to the initial fricative. The possibility that this was due to improper voiced-unvoiced vocoder decisions was ruled out by a test in which only unvoiced excitation was used in the synthesizer. Voiced responses were still in evidence, indicating that these errors were due primarily to spectral-energy distributions. Consequently, the properties of fricatives and fricative-vowel transitions were investigated in detail. The results of (a) sonagram analysis of the samples, (b) digitized power-spectrum information provided by the AFCRL digital speech processor, and (c) waveform analysis are discussed. [The research reported in this paper was supported by the U. S. Air Force Cambridge Research Laboratories, Office of Aerospace Research, under Contract AF 19(628)-389.]
Transmission Loss of Leaded Building Materials. II.
Authors: Ostergaard Paul B. , Goodfriend Lewis S.
Published: November 2005

A total of 24 partitions with lead laminated to the core or one face have now been tested for sound isolation. The results confirm that lead will improve the transmission loss of many partitions above what can be achieved with the same weight and thickness of the base material. The superiority of lightweight sheet lead on each leaf over a single heavy sheet on only one side is indicated. A 312-in.-thick panel of plaster on gypsum lath with lead supported each side of 138-in. steel studs and yielded an average of 48 dB (9 frequency) and a sound-transmission class of 50 dB. The lead, weighing 3.85 lb/sq ft (0.65 in.), was laminated to the lath on each side. Total panel weight was 21.8 lb/cu ft, less than many masonry partitions. [This work was supported by the Lead Industries Association-Expanded Research Program.]
Dynamic Encoding as Applied to a Channel Vocoder
Authors: Steele Robert W. , Cassel Lawrence E.
Published: November 2005

In a conventional channel vocoder, the output of the analyzer is encoded on the basis of a preset dynamic range. The number of quantizing steps utilized to describe the totality of analyzer outputs is, therefore, a function of the correspondence of the sampled analyzer dynamic range and the preset dynamic range of the encoder. If the analyzer level variation for every sampling interval perfectly matched the dynamic range of the encoder, then the encoder would provide complete and efficient description of the analyzer outputs. The process of dynamic encoding provides just such a match. It automatically varies the encoder dynamic range to match the range of the analyzer outputs. This paper describes the technique for accomplishing the dynamic encoding principle in a channel vocoder. Results indicate a 3% to 4% PB word-score improvement in a conventional 2400-bit channel vocoder. Such a technique is also applied to lower the channel-vocoder bit rate to 1200 bits/sec.
Effect of Transmission Errors on the Intelligibility of Vocoded Speech
Authors: Steele Robert W. , Cassel Lawrence E.
Published: November 2005

Much time and study is being devoted to the improvement of vocoder-speech quality and intelligibility. One factor that is being neglected, however, is the effect of transmission errors on the intelligibility of vocoded speech. To evaluate this effect, a full duplex 16-channel Philco vocoder is employed. Errors are inserted into the PCM output of the transmitter at various rates and in a random fashion. Intelligibility tests are run to determine the loss of intelligibility with increasing error rates. Curves are plotted showing these effects for a number of speakers. Fixed-position errors are also inserted within the pitch portion of the bit frame and similar intelligibility test, are run. Results for the random insertion of errors indicate that an error rate of 1%–2% (1 to 2 bits per 100) is tolerable, before any appreciable loss in the zero-error PB word intelligibility of 85% is apparent. At a transmission-error rate approaching 5% (5 incorrect bits per 100), the channel vocoder is capable of a PB word intelligibility of 75%, corresponding to a sentence intelligibility of 93%. Comments on the loss of speech quality with increasing errors are also given. Error insertion in the pitch portion of the frame indicates a surprising ability of the channel vocoder to tolerate error while maintaining intelligibility.
Comparative Evaluation of Pitch-Signal Indicators
Authors: Wallace John C.
Published: November 2005

An evaluation of several pitch-extraction methods has been carried out with respect to, e.g., the time delay between the presentation of the speech signal and the pitch period indicating pulses for that signal, the occurrence of spurious pitch-period indications, etc. For comparison, an ideal pitch-period-indicating signal was generated. The method of generating this ideal signal consists of a manual recording of the individual pulses to indicate accurately the onset of each pitch period, as determined by eye. Results obtained with both instantaneous and short-time average fundamental-frequency pitch indicators are presented and their relative merits discussed. [The work reported was sponsored by the National Science Foundation under Grant GP-590.]
On Spectra and Directivity of Jet Noise
Authors: Ribner H. S.
Published: November 2005

The present study develops a more quantitative picture of the relationship of jet noise to the turbulent structure of the jet. The work appears to predict qualitatively the changing directivity in different octave bands and at least in part the apparent paradox of a “reverse Doppler shift” of the spectrum peak. On the assumption of locally isotropic turbulence superposed on the mean jet flow, the broadly peaked noise spectrum is derived in terms of a sum of two bell-shaped spectra peaked an octave apart. The proportions vary with direction θ from the jet axis, being dominated by the “bass” spectrum at small angles and the “treble” spectrum beyond, say, 70°. This is accomplished by a factor ∼cos4θ for the “bass” spectrum. For small angles (e.g., 30°), points of the resultant curve are amplified (vertical shift) by convection of the eddies and “Doppler-” shifted (less than the full amount) in frequency. It is suggested that an increase in amplification toward the left may move the amplified peak in that direction. This could occur if, somewhat downstream of the potential core, the dominant noise emitters were located sufficiently close to the axis to be convected substantially faster than those in the mixing region.
Transition to Turbulence near a Flexible Interface
Authors: Karplus Henry B.
Published: November 2005

Transition to turbulence was observed in water flowing in a narrow rectangular channel provided with a flexible interface by making use of measurements of instantaneous velocity, as indicated by a deposited-film constant-temperature anemometer. The characteristics of the transition from laminar flow near the entrance of the channel to the fully turbulent condition downstream may be described as consisting of a series of random bursts of flow fluctuations separated by steady-flow conditions. The number of turbulence bursts in unit time interval increases monotonically on a sigmoid curve in the transition region. A measure of the degree of turbulence based on a counting technique was developed for this study. Transition to turbulence sets in earlier for some types of flexible surfaces than it does for rigid walls. However, the rate of increase was greatest for the rigid walls. [This work was sponsored by the David Taylor Model Basin.]
Properties of Cylindrical Arrays of Circular Rings
Authors: Camp Leon
Published: November 2005

This report is concerned with the properties of transducers using no pressure release and, consequently, unaffected by hydrostatic pressure. Experimental results show that cylinders of a height 0.1 λ of the projected sound are free of spurious resonant effects and may have an efficiency of 75%. The radiation pattern is a toroid 120° wide at −6 dB and is down 20 dB along the cylinder axis. Such cylinders, or rings, are suitable as elements in a cylindrical array when properly spaced. For example, four elements having a diameter-to-wall-thickness ratio of 60 and being evenly spaced to a total length of 0.75 λ result in a Q of 4, a toroidal beam pattern 68° wide, down 30 dB on the axis, and 75% efficiency.
Propagation of Spherical Pulses from Water to Air
Authors: Dyer I. , Malme C. I.
Published: November 2005

The generation of a pressure pulse in air by an underwater explosion may involve several physical mechanisms, such as the transmission of the underwater pulse through the interface, and the dome formation, plume formation, and gas venting at the interface. We consider initially the mechanisms of the underwater-pulse transmission and dome formation. Except for very intense underwater explosions, it is expected that the transmission of the pulse through the water-air interface will be predicted closely by linear (infinitesimal} theory. Dome venting is associated with underwater cavitation of the reflected rarefaction wave at the interface and may occur even when the underwater pulse is infinitesimal. To study these mechanisms experimentally, we use small nonfragmenting and nongasproducing explosives that generate underwater pressure peaks equivalent to those generated by about 10−7 lb of TNT. The pulses generated in air above the water are measured. An analysis of the data relevant to the mechanisms of the underwater pulse transmission and the dome formation is presented. [This research is supported by the U. S. Naval Ordnance Laboratory.]
Propagation of Explosive Energy in Water near a Model Ocean Floor at Very Near Ranges
Authors: Spitznogle Frank R.
Published: November 2005

The problem of the prediction of the acoustic pressure field in a liquid near a solid interface due to an explosive sound source in the liquid is discussed. Ranges of interest are of the order of a few wavelengths or less. A recent theory by E. Strick is considered and found to be applicable to the stated problem. Extended model data similar to those gathered by Roever and Vining in verifying the aforementioned theory are presented, which show remarkable experimental-theoretical agreement. The extension of the theory to a stratified solid media is carried out and model results are presented that appear to agree with theoretical results. Results illustrate that the presence of interface arrivals is strongly dependent on the mean wavelength emitted by the explosive source and the thickness and rigidity of the layers in the assumed solid, as might be expected. It is concluded that this theory may prove useful in investigating the propagation of low-frequency acoustic energy from impulsive or explosive sound sources near a solid ocean bottom at ranges of a few wavelengths or less.
Spontaneous Activity of Single Auditory Nerve Fibers in Cats
Authors: Kiang Nelson Y.-S.
Published: November 2005

In a study of over 100 auditory nerve fibers, every fiber exhibited spontaneous spike discharges although the rates ranged between <1/sec to 100/sec. Histograms of the interspike interval of this activity all show a mode at about 4 msec and a tail that decays exponentially. This pattern is consistent with that generated by a Poisson-like process with a dead time. A histogram of the number of fibers encountered vs spontaneous rate shows that certain ranges of rates occur more frequently than others. Distinct peaks occur at <5/sec and 40/sec with less distinct peaks at 60/sec and 70/sec. This distribution of spontaneous activity can be seen in individual cats and is apparently unrelated to either physiological condition or level of anesthetization of the animal. There is no correlation of rate of spontaneous discharge with the frequency of tone to which the unit is most sensitive. However, there is some indication that units with low rates of spontaneous discharge have higher thresholds to acoustic stimuli than units with high spontaneous rates. [This work was supported in part by the U. S. Army, U. S. Air Force Office of Scientific Research, and the U. S. Office of Naval Research; in part by the National Science Foundation (Grant G-16526): in part by the National Institutes of Health (Grant MH-04737-02); and in part by research grant B-1344, National Institute of Neurological Diseases and Blindness, National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare.]
Some Parameters of Unit Response Patterns in Cochlear Nerve of Cat
Authors: Moushegian George
Published: November 2005

Electrophysiological experiments show that single units of the cochlear nerve of cat exhibit a variety of responses. Some units discharge with interspike intervals that are equal to or some multiple of the period of the stimulating tone. In contrast, other units discharge with spike intervals that can not be related to the period of the stimulating tone. With increase in intensity, some units show a systematic decrease in interspike intervals, unrelated to the period of the sinusoid. Instead of transmitting frequency information, these units perhaps convey primarily intensity information. It is shown that the spontaneous discharges of afferent as well as efferent nerve fibers are inhibited by sound, the former promptly with the onset of the tone and the latter over a much longer time course. Evidence is presented that two modes of inhibition—herein called afferent and efferent inhibition—occur in cochlear-nerve units. The role of efferents in auditory activity has recently been investigated by Fex. With regard to afferent inhibition, Hartline et al. have shown inhibition of impulses from an ommatidium of the Limulus eye upon illumination of a neighboring ommatidium, presumably via fibers between their axons. The possibility that such a plexus exists within the cochlea merits some consideration for understanding afferent inhibition.
Auditory Activity in Crossed and Uncrossed Olivocochlear Neurons and Effects of the Crossed Efferents on Intracochlear Events
Authors: Fex Jörgen
Published: November 2005

In decerebrate cats, the vestibulo-cochlear anastomosis was exposed through the vestibulum. Activity of crossed and uncrossed olivocochlear fibers identified as such was recorded with micropipette electrodes in the anastomosis. Sound stimulation of the contralateral ear activated both kinds of efferents, as did electrical stimulation of the ipsilateral cochlear nerve. The fibers responded characteristically with a low, regular firing rate. In some fibers, there was summation for the two modes of stimulation. Some of the uncrossed efferents could be inhibited by sound. Fibers in the basal fascicle of the vestibulo-cochlear anastomosis generally responded to higher tone frequencies presented to the contralateral ear than did fibers in the apical fascicle. This suggests that afferents and efferents, both crossed and uncrossed, from homotopic cochlear points in opposite cochleae are connected. In decerebrate cats with both inner ears intact, the effect of electrical stimulation of the crossed efferents was studied with macroelectrodes at the round window and with microelectrode recording from single primary auditory neurons. Such efferent stimulation diminished the action potential (Galambos, 1956), increased the cochlear microphonics (Fex, 1959), and increased the resting potential at the round window. Resting activity, as well as sound-evoked activity, in single primary auditory neurons was inhibited.
Simple Harmonic Source in a Slightly Irregular Waveguide
Authors: Clay C. S.
Published: November 2005

The normal-mode solution of the problem of the radiation field of a simple harmonic source in layered waveguide is extended to the case of small irregularities in the surface. The theory is used to calculate the radiation field of a 147.8-cps simple harmonic source in about 20 m of shallow water over a thick layer of unconsolidated sediments. The calculations indicate that the effects of small surface roughness (i.e., rms waveheight about 12 m) are to increase the attenuation as a function of range and to decrease the mode-interference maxima and minima. The experimental dependence of the acoustical pressure upon source distance is similar to that calculated with the theory. [Hudson Laboratories, Columbia University Informal Documentation No. 26. This work was supported by the U. S. Office of Naval Research.]
On the Acoustic Modeling of rf Propagation
Authors: Lee David A.
Published: November 2005

Model measurements of the radio frequency (rf) scattering patterns of complicated objects and radiation patterns of new reflector or array antennae are often desirable. Unfortunately, it is difficult to generate and control rf energy of sufficiently short wavelengths for models of convenient size. Acoustic radiation of very short wavelengths is relatively easy to produce, and one has hopes of determining rf scattering and radiation patterns from measurements made with conveniently small acoustic models. In this article, the farfield intensities of rf and acoustic plane waves scattered by perfectly reflecting objects are found to be identical only in the geometric-optics limit, and a simple relation is found between the farfield patterns of certain acoustic and rf-dipole arrays.
Propagation of Longitudinal Waves in a Weakly Ionized Gas
Authors: Sessler Gerhard M.
Published: November 2005

The propagation of longitudinal waves in a weakly ionized gas consisting of three species of particles (neutrals, ions, and electrons) is analyzed, giving full consideration to the influence of collisions between all three kinds of particles. The calculations are based on Euler's and Maxwell's equations. Damping and phase constants for the neutral-particle sound wave, the ion wave, and the electron wave are presented for different values of particle densities and for frequencies lower than or comparable to the plasma frequency of the ions. The limitations of this approach, especially at frequencies higher than the plasma frequency of the ions, are discussed. The main result of the calculations is that in a certain frequency range the damping of the ions wave can be smaller than the damping of the neutral-particle wave. This suggests the stimulation of ion waves by means of acoustic transmitters. Such an ion wave would be free of the potentially disturbing neutral-particle wave at some distance from the source. In contrast to other methods, this method makes it possible to stimulate a purely longitudinal plane wave.
Sound Absorption in Liquid Metals
Authors: Letcher S. V. , Beyer R. T.
Published: November 2005

Sound absorption in liquid sodium and potassium has been measured from the melting point to 150°C in the frequency range 20–80 Mc/sec. Best available data for the classical absorption coefficient indicate that α/f2 for sodium has the classical value, whereas α/f2 for potassium has a slightly higher value. Measurements in mercury over a comparable range also yielded α/f2 slightly greater than the classical value in agreement with Hunter, Storey, and Lewis [J. Acoust. Soc. Am. 34, 742 (1962)]. Velocity measurements (accurate to ±1%) are in agreement with those of Pochapsky and Quimby [Phys. Rev. 79, 892 (1950)] and Ilgūnas and Baršauskas [Kauno Politech. Inst. Darbai 5, 157 (1957)]. The dependence of the absorption in liquid sodium on the sound frequency and field intensity in an external, dc magnetic field up to 12 kG was also studied. Qualitative agreement with the predictions of the equations of Anderson [J. Acoust. Soc. Am. 25, (1953)] was found, indicating the onset of magnetohydrodynamic interaction in the region below 15 Mc/sec.
Sound Radiation from Spinning Vortices
Authors: Powell Alan
Published: November 2005

The basic theory of sound fields induced by vorticity [see “Vortex Sound,” Dept. Eng. Rept. 61–70 (1961)] is briefly reviewed, and applied to the following situation. Two parallel rectilinear vortices of length l and of the same circulation Γ are distance 2y apart, and spin about the axis lying between them. The sound field is like that of a lateral quadrupole, rotating with the spinning flow field, the directional pattern somewhat resembling a doughnut, without a hole, threaded on the axis of spin. The maximum amplitude of the pressure perturbation at distance x is very easily shown to be (ρ0/xc02)(Γ/4πy)4l, where ρ0 is the fluid density and c0 is sound speed. This simple result applies to weak vortices, Γl/(2πy2c0)≪1. The rotating quadrupole may be represented by sinusoidally varying fixed quadrupoles, either by one lateral one together with longitudinal ones of opposite sign aligned along each of the axes of the lateral ones, or by two lateral ones that have their axes bisecting each other. The sound power is shown to be (16/15π)(ρ0/c05)(Γ/4πy)8l2. Since Γ/4πy is the induced velocity of the vortices, the sound power follows the eighth-power law of aerodynamic noise. [Partial support for this work has been provided by the U. S. Office of Naval Research under contract.]
Simplified Treatment of Scattering
Authors: Harrison Mark
Published: November 2005

For the scattering of a scalar wave, the total scattering cross section is generally expressed as σ = (4π/k2) × Σ(2l+1) sin2δl. This expression and the values for the phase shifts δl are usually obtained from given boundary conditions at the scatterer. It apparently has not been recognized in the acoustical literature that the above formula can be argued by considering only asymptotic conditions far from the scatterer. This procedure has been used in nuclear physics where, due to the absence of knowledge concerning the scatterer, asymptotic arguments are necessary. While a little thought renders it evident that such a procedure can be adopted to acoustical scattering, apparently it has not been specifically pointed out. In this paper, it is shown how to obtain the above scattering formula independent of the nature of the scatterer. Of course, there leaves the problem of obtaining the phase shifts δl. It is also shown that for an arbitrarily specified scattering region it is also possible to use the asymptotic arguments to obtain a general formula for computing the phase shifts in many practical problems. [This work has been supported by the U. S. Office of Naval Research.]
Passive Vibration-Cancelling Isolation Mounts
Authors: Sykes Alan O.
Published: November 2005

The design of passive vibration-cancelling isolation mounts is discussed. Design criteria for a single-frequency vibration-cancelling mount and experimental data for a crude prototype are presented.
Lateral Vibrations of a Beam with the Added Effects of an Axial Force on Many Support
Authors: Saunders H.
Published: November 2005

A method is presented for determining the natural frequency in bending of a beam subjected to an axial force. The analysis involves the use of “transfer matrices” to represent the characteristics of point and field elements of the column. The transfer matrix is defined as an array of coefficients that relate conditions on load, deformation, shear, moment, and slope across an element of the structure. The transfer matrix for an element is actually a square array. For the case of a beam in lateral bending, this is 4×4 matrix. The general method of “transfer matrices” is applied in determining the natural frequency of a multisupport beam under axial force consisting of restrained linear and torsional springs, sliding support, and a concentrated load.
Resonance of a Periodically Supported Beam and Its Coupling to Sound
Authors: Smith P. W.
Published: November 2005

The periodically supported beam is an example of a linear chain of identical structures with coupling between nearest elements. A sequence of pass- and stop-bands of frequency exists for wavemotion in the infinite structure. Resonances of a finite structure cluster in the passbands. The analysis accounts for nonvanishing rotary impedance of the supports. Because of the supports, each passband has modes with acoustically effective wavelengths ranging from twice the support spacing to twice the over-all length. Coincidence effects and efficient and directional coupling to sound occur at much lower frequencies than in the case of the unsupported beam. [This work was supported by the National Aeronautics and Space Administration.]
Overpressure and Dynamic-Pressure Impulse Resulting from High-Intensity Explosion
Authors: Wong D. M. , Lee S. Y.
Published: November 2005

This paper discusses the overpressure and dynamic-pressure impulses resulting from a disturbance of the air caused by high-intensity explosion. The impulses as functions of distance from the center of explosion are theoretically investigated and compared with the latest available experimental data on explosion. The parameters discussed include an explicit investigation of the definition of the shape and the duraction of the positive and negative phases of both the dynamic pressure and the overpressure impulses. The experimental data are evaluated with the aid of an IBM computer program to calculate the total momentum resulting from the pressure-time profiles of the full-scale explosion tests. Following the theoretical approach of G. Taylor and H. L. Brode, the positive overpressure phase is given by IP+ = K1(W/P0)12/R. The positive dynamic-pressure phase is IQ+ = A(W/P0)1/6/R12×[B + R2(W/P0)12]. The negative overpressure impulse is IP− = K2Pm, and the negative dynamic-pressure impulse is IQ− = CQm. The notations are R the distance from the center of explosion, P0 the initial atmospheric pressure, Pm the minimum overpressure, Qm the minimum dynamic pressure, W the total energy released, and K1, K2, A, B, C are constants to be determined from the experimental data obtained by the Ballistic Research Laboratories.
Light Diffraction by Ultrasonic Waves (Oblique Incidence)
Authors: Mayer Walter G.
Published: November 2005

The diffraction of light by plane, progressive ultrasonic waves in water is investigated experimentally for conditions where pure diffraction effects and Bragg reflections might be expected to occur simultaneously. Experimental results are given for frequencies between 3 and 12.3 Mc/sec and for angles between the direction of sound and light propagation within ±1° of normal incidence. The results are compared with theoretical predictions. [Supported by the Office of Naval Research, U. S. Navy.]
Effects of an Absorbing Bottom on Shallow-Water Normal-Mode Propagation
Authors: Bucker H. P. , Keir D. L.
Published: November 2005

Recordings have been made of the arrival of sound produced by explosives in shallow water of from 100–160 ft in depth and at ranges up to 80 kyd. Vibrational analysis of these recordings clearly indicates that the sound travels as normal modes. The dispersion of the first 3 modes can be determined in most cases and 5 modes appear in several records. This paper presents some of these experimental mode-dispersion curves and outlines a theory that explains the experimental results. The theory utilizes the ray approach to the normal-mode problem, with the effects of an absorbing bottom introduced into the theory as a consequence of the phase shift of the ray on bottom reflection. Since the recorded sound can be resolved into normal modes, the energy that arrives at a certain time with a particular frequency can be identified as the arrival of a ray with a definite angle. With this method of identification, the reflection coefficient of the bottom can be determined as a function of frequency and angle for small grazing angles and low frequencies.
Long-Range Sound-Transmission Measurements in the North Atlantic Ocean
Authors: Urick R. J.
Published: November 2005

Although the qualitative aspects of long-range transmission in the deep sea have long been known, little has been reported about its quantitative features, other than travel time, since the pioneering work of Ewing and Worzel nearly 20 years ago. In the present work, standard Navy Sofar bombs, dropped by an aircraft at intervals of about 100 miles between Bermuda and the British Isles, were recorded at Bermuda on hydrophones at various depths. For a Sofar-axis hydrophone and for shots dropped between Bermuda and the Azores, an energy-transmission loss of the form 10 log r0r+ar was found, where r0 is a transition range between spherical and cylindrical spreading and a is an attenuation coefficient. r0 was found to be about 2000 yd, in rough agreement with the hypothesis that the energy carried by a ray bundle becomes diffused throughout the channel width it occupies. The attenuation coefficient was found to be of the form A+Bf, and to be much higher than that caused by absorption alone. The mid-Atlantic ridge produced a loss of 5 and 15 dB for shots at 1500 and 3500 ft. In the absence of this loss, a maximum range of 7000 miles for a 4-lb Sofar bomb would be predicted.
Pressure-Sensitivity of Accelerometers
Authors: Schloss Fred
Published: November 2005

The pressure sensitivity of accelerometers has been determined in the frequency range from 20–2000 cps by immersing the transducer in a vibrating column of liquid, as has been suggested by Sykes. If the sensitive axis of the transducer is oriented perpendicular to the axis along which the liquid column vibrates, the transducer will remain at rest, since the pressure gradient along the sensitive axis of the transducer is zero. The pressure sensitivities thus obtained are lower than the acoustic sensitivities obtained in air, using other methods. Various aspects are discussed, such as the frequency dependence of the pressure sensitivity and the pressure sensitivity of cables.
Analysis of a Computer Simulation of a DIMUS System
Authors: Rodgers George F.
Published: November 2005

In the usual shift-register/delay-line arrangement, as detailed by Anderson (1960, 1961) and Rudnick (1960), geometry of the array, in conjunction with sound velocity in the medium, establishes a time delay for each wavefront arrival at a particular phone. The pressure waveform is then stored in each shift register, and is then clocked at a rate sufficiently above the Nyquist frequency, such that degradation of zero crossover information is avoided. Sampling the shift-register matrix, at points appropriate to the array geometry, will result in a gain for the signal emanating from a given direction. One characteristic feature of the DIMUS system is an amplitude normalization, which devolves from the binary nature of quantization. Thus, from the maximum signal-to-noise ratio to the minimum, from +∞ to −∞ dB, a response ratio corresponding to the directivity index is achieved. For 100 hydrophones, this range would be 20 dB (re power); for 10 phones, 10 dB, etc. The levels are thus predictable, regardless of pressure level of the source as seen at the array. The paper discusses the analytic and computer simulation aspects of these phenomena. Correlation functions are derived analytically and compared with simulation results for several cases.
Application of Experimental Vibration Data to the Design of Viscoelastic-Damped Structures
Authors: Ruzicka Jerome E.
Published: November 2005

Various theoretical analyses of idealized structural elements embodying a viscoelastic shear-damping mechanism are available in the technical literature. The damping properties of viscoelastic-damped beams, plates, and simple structural junctions have been investigated with simplifying assumptions made with regard to the uniformity of structural-member cross section, the type of mass-loading distribution, and the nature of physical constraints and boundary conditions. Actual structural fabrications associated with electronic and electromechanical equipment require appropriate consideration of concentrated mass loadings, boundary conditions, fastening devices, strength requirements, and environmental conditions. This paper discusses the application of experimental vibration data to the design of viscoelastic-damped structures and presents a number of examples in which viscoelastic shear-damping materials have been employed in the fabrication of structures for modern electronic and electromechanical equipment. Experimental data are presented for a laboratory electronic-chassis model, an antenna gearplate, an aircraft equipment-mounting rack, a gyroscope-mounting system, a missile flap-actuator relay panel, two missile-arming and -fusing structures, and a satellite decoder-receiver electronic equipment. In most cases, the structural-damping property of the system is measured before and after the application of a viscoelastic damping treatment in order to indicate the degree of vibration control that has been provided.
Use of Damping Materials for Noise Reduction on Railway Carriages and Other Equipment
Authors: Cheesman G. C. N.
Published: November 2005

Noise-level measurements are described that were carried out on a British Railway's buffet car both untreated and with two different levels of treatment. The whole carriage, walls, floor, and roof were sprayed with a high-efficiency vibration-damping material that reduced the noise over the whole frequency spectrum. There was also high-frequency airborne noise coming up through the floor, which required a separate treatment. The average drop was 7 dB. Possible alternative damping systems and alternative methods of application, such as preformed heat-fusible damping sheets, are discussed. Noise-level measurements are also described for the driver's cab of a diesel locomotive and for domestic equipment, such as washing-machine spin driers.
Effect of Noise Crosscorrelation on Binaural-Signal Detection
Authors: Langford T. L. , Jeffress L. A.
Published: November 2005

This is an extension of a study of the effect of the interaural correlation for a masking noise upon the detection of a tonal signal reported in 1953 by Jeffress, Blodgett, and Deatherage. As in the previous study, the crosscorrelation of the noise in the critical band was varied by introducing a time delay into the noise channel to one ear. Data were obtained in a two-interval forced-choice experiment, and the data for the time-delayed conditions are presented as masking-level differences (MLD) relative to the undelayed condition (homophasic). There is a rapid release from masking as the crosscorrelation is reduced from unity with a less rapid release for the negative values of correlation. The function relating MLD's to values of correlation is cyclic and becomes damped as the noise delay is increased through several periods of the signal frequency. Data for conditions in which the signal is reversed in phase at one ear are also presented. The results are compared with those of a study reported by Robinson and Jeffress in 1962 in which the interaural correlation of the noise was varied.
Intensity Discrimination for Thermal Noise
Authors: Campbell Richard A.
Published: November 2005

The ability of human observers to detect a thermal-noise signal (S) immersed in a thermal-noise background (N) has been studied. Subjects were asked to correctly identify, in a two-alternative forced-choice situation, the time interval in which S occurred. Signal-to-noise ratios in dB based on steady-state voltage measurements (S/N), were varied automatically according to the subject's performance on a block of 12 trials. The S/N was varied in 1-dB steps until a 75% correct-detection level was maintained. The raw data were the median S/N presented in a 252-trial session. Variables considered were the duration of S and the sensation level (SL) of N S/N's obtained decreased linearly with log time from 1 msec (+4 dB) to 100 msec (−7 dB), then approached a minimum (−9 dB) at 1 sec duration. If these same S/N's are converted to increments [(S+N)/N]] and expressed in dB, a nonlinear decrease, with log time, results, decreasing from 5.5 dB at 1 msec to a value approaching 0.5 dB at 1 sec duration. The question considered is whether S/N or (S+N)/N is the effective stimulus to the subject. S/N is a negatively sloped nonlinear function of SL, decreasing between 10 and 90-dB SL. Deviations from this function are seen around 60 and 70 dB SL. These deviations and the placement of the function on the S/N axis are related to rise/fall time of S and bandwidths of S and N.
Model for Monaural-Pulse Interval Discrimination
Authors: van Bergeijk Willem A. , Harmon L. D. , Levinson J.
Published: November 2005

A model is proposed to account for some auditory click-fusion results obtained by Guttman, van Bergeijk, and David several years ago. These results showed that the critical time interval between the members of a click pair at which each member could just be separately perceived (as measured by binaural fusion) was a function of the repetition frequency with which the pairs were presented. As repetition frequency went up, the critical interval decreased. The model postulates that each click is represented in the nervous system by a short burst of spikes. A low-pass neural filter (or integrator) is assumed not to resolve the individual spikes in a burst, but rather to “see” the burst as a single event. With an interburst interval longer than the interspike interval within a burst, the filter would see two events. The shorter the bursts, the closer the events can be spaced. A single-neuron model is proposed that generates bursts in response to single input spikes; the length of these bursts decreases with increasing input frequencies. The model has two critical parameters: one is the time constant of the excitatory input, which is short, and the other is the time constant of an output-derived inhibitory feedback, which is long.
Pitch Discrimination by Air Conduction and by Bone Conduction for Sonic and Ultrasonic Frequencies
Authors: Corso John F. , Levine Murray
Published: November 2005

In an earlier paper (1962), the principal investigator reported bone-conduction thresholds from 5–100 kc/sec and indicated that high-intensity bone-conducted sounds were capable of producing auditory sensations in normal-hearing subjects. The present study was performed to investigate pitch discrimination for sonic and ultrasonic frequencies presented monaurally by air conduction and by bone conduction. Five groups of 5 subjects each, screened for normal hearing and high-pitch ability, were tested in an anechoic chamber from 2–54 kc/sec at a loudness level of 20 phons by the method of constant stimuli. The results indicate that (1) from approximately 4–14 kc/sec, the difference limens for pitch discrimination by bone conduction are smaller than those for air conduction, and (2) pitch discrimination is absent for bone-conducted tones in the ultrasonic region. The difference limens for bone conduction vary from a minimal value of 7 cycles at 2 kc/sec to 134 cycles at 14 kc/sec; for air conduction, the difference limens vary from a minimal value of 7 cycles at 2 kc/sec to 148 cycles at 14 kc/sec. The significance of these data for auditory theory is discussed. [This research was supported by Grant B-2006 (R1) from the National Institute of Neurological Diseases and Blindness, National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare.]
Computer Simulation of a Formant-Vocoder Synthesizer
Authors: Crystal Thomas H. , Meinhart Dagmar
Published: November 2005

An extremely versatile, moderate-speed, sampled-data simulation of a resonance vocoder has been achieved. The synthesizer is an elaboration of its predecessor [J. L. Flanagan, C. H. Coker, and C. M. Bird, J. Acoust. Soc. Am. 34, 2003 (A) (1962)]. It accepts voicing, hiss resonance, and antiresonance data at a 100-cps rate and computes 20-kc/sec, 4096-level, sampled speech. The versatility in the form of easily programmed changes in circuit wiring and tuning is being exploited to test quality factors of synthesized speech. The moderate simulation speed of approximately 70 times real time on an IBM-7090 with IBM-1401 input-output will provide for economy in an extended testing program. Versatility has been accomplished by programming the synthesizer in the block-diagram-compiler (BLODI) format and by devising new circuit blocks for special functions and for decreasing computation time. Particular care has been taken to achieve proper s-plane synthesis, using z-plane techniques, and to minimize quantization noise, errors, and instability.
Digital-Computer Simulation of a Sampled-Data Voice-Excited Vocoder
Authors: Golden Roger M.
Published: November 2005

A sampled-data system representing a 10-spectrum channel voice-excited vocoder (VEV) has been simulated on an IBM-7090 digital computer. The usefulness of the simulation lies in the fact that it permits studying readily the effects of changes in major vocoder parameters, such as excitation, analyzing and resynthesizing filter bandwidth, etc., without the lengthy waiting periods required for equipment changes. In addition, the program can be used for studying vocoder-channel multiplex problems. Programming for the simulation was expedited by the use of a special program compiler developed at Bell Telephone Laboratories. The compiler permits specification of a sampled-data system in functional-block form. The system represented by the simulation was, in general, realized by determining sampled-data equivalents of the filters and circuits used in an analog VEV. However, the great number of bandpass filters needed were synthesized by using a unique and computation-time-saving design. Speech processed by this simulated sampled-data system is of excellent quality and often is better than that processed by some analog VEV's. The program requires about 172 sec to process 1 sec of recorded speech.
Voice-Communications Method, Using Pattern Matching for Data Compression
Authors: Smith Caldwell P.
Published: November 2005

A pattern-matching technique for compressed digital voice communication was investigated. The method, based on the use of vocoders for input- and output-speech processing, used digital spectrum pattern matching for real-time compression and expansion of speech. From analysis of speech samples, catalogs of voice patterns were compiled together with data on the probabilities of occurrence of the voiced and unvoiced spectrum patterns comprising the distributions, and the average intensity level at which patterns occurred, as functions of the fidelity criterion used in classifying patterns. A strategy was established for constructing tables of pattern stereotypes, in which the fidelity criterion assigned to pattern classes was ordered as a function of pattern probability, such that frequent patterns would be matched and encoded with high precision, infrequent patterns with a larger tolerable input/output error, on a 7-valued fidelity scale. The pattern tables assembled in this manner were utilized for real-time pattern matching, in which voice samples were analyzed, categorized in terms of a “best match” among the pattern stereotypes, and synthesized from the “standardized” patterns. Speech-data items were encoded as independent samples at 50 items per second; the information-data rate was 250 bits per second for pitch data (5 bits per sample), plus 50 (n) bits per second for pattern data, where 2n = Np (number of pattern items comprising a catalog). Input/output pattern error distributions were compiled to test the efficacy of this strategy in minimizing the average errors between input and output patterns for a given catalog size for pattern matching.
Spectrum-Pattern Data for Speech Samples Measured with “Differencing” Filters in Comparison with Data from Conventional Filtering
Authors: Smith Caldwell P.
Published: November 2005

Recorded speech samples were measured with an 18-channel spectrum analyzer of contiguous 3-pole bandpass filters covering the range from 200 cps–5 kcps using conventional rectifiers and lowpass filters, in comparison with an arrangement in which analog combining circuits were used to perform “second differencing” of the output-voltage signals from the spectrum analyzer. The differencing technique, first proposed by Huggins, combines signals with groupings of three adjacent channels, using weights of −1, +2, and −1 to derive a “sharpened” filter-response characteristic. The data were digitized and distributions were compiled to determine effects of spectrum-pattern simplification as revealed in pattern statistics and in cumulative level distributions for the 18 spectrum channels. Speech was synthesized from the “sharpened” spectrum data to examine effect on speech intelligibility and quality. The differencing technique tends to simplify spectrum data such that the channel signals in the vicinity of major peaks of the voice-spectrum patterns are retained.
Report on the Feasibility of Multiplexing Teletype Data into the Nonspeech Times of Vocoded-Speech Transmission
Authors: Smith C. P. , Ziemer D. R.
Published: November 2005

This paper presents the results of an analysis to evaluate the feasibility of multiplexing teletype data into the nonspeech times of vocoded speech transmission. The increase in channel-utilization efficiency that acrues due to the multiplexing is described in detail. In the course of appraising the merits of the multiplexing technique, a full-scale simulation of the postulated system was performed on a digital computer. In this manner, the efficiency of transmission rate was studied with regard to (1) number of teletype channels available as input, (2) required buffer storage, and (3) statistical characteristics of speech and nonspeech distributions in spoken text and typical conversation classifications of long-distance voice communication. A discussion of the simulation procedure is given, complete with operational curves. The equipment necessary for implementing the multiplexing operation within the polymodal vocoder designed and built for AFCRL is described in detail.