bluuebunny/crossref_metadata_2025 huggingface dataset:
Recognition of Repeated Patterns: A Study of Short-Term Auditory Storage
Authors: Schubert Earl D. , West Roger A.
Published: October 2005

The parameters of waveform that enable listeners to recognize repetition of patterns within a signal were explored by using four types of waveform called random-amplitude constant-period, constant-amplitude random-period, random-amplitude random-period cophasic, and random-amplitude random-period antiphasic. The measure used for comparison was the number of repetitions per signal required to differentiate signals containing repetitions from random waveforms that did not contain repetitions. In the first experiment reported, the subject's performance was kept at 75% correct differentiation by varying the number of repetitions per signal. The comparisons were made among all four types of waveforms at each of three sensation levels: 20, 50, and 80 dB. Signals with zero-crossing information (random period) and signals of medium sensation level appear best for recognition of the repetition of patterns. In the second experiment, the same type of signals were high-pass or low-pass filtered, and similar comparisons were run. Although absolute comparisons were not possible, it appears that high-frequency information is more useful than low to the auditory system in identifying the repetitions within signals. A third experiment explored the possibility that one type of signal waveform is more readily learned than another. To make the task more difficult, segments of either noise or silence were inserted between the repetitions of the patterns, and were introduced with the same spacing into the nonrepeated waveforms. Repetition of pattern was still too easily recognized by the subjects, and no evidence of any difference in rate of learning to recognize patterns was found for the different types of waveform.
Hearing Threshold and Ear-Canal Pressure Levels with Varying Acoustic Field
Authors: Shaw E. A. G.
Published: October 2005

A well-damped circumaural enclosure is equipped with five independent acoustic driver units located at cardinal positions. The acoustic field near the external ear may thus be varied in a manner corresponding to angle of incidence. The acoustic pressure at a well-defined position at the ear-canal entrance is measured with a probe tube passing under the circumaural cushion. With each subject and frequency, the driver voltage level at hearing threshold LC and the ear-canal response REC are determined for each driver unit in turn. A double series of measurements has been made with six subjects from 1–12 kHz and three to six subjects from 13 to 16 kHz at 1-kHz intervals. The ear-canal pressure level at hearing threshold LE is found to be virtually independent of the acoustic-field geometry up to 12 kHz. Changes in LC and REC observed after a one-week interval can be related to three independent mechanisms: (1) changes in subject hearing sensitivity, (2) changes in coupling between probe-tube orifice and ear-canal wave pattern, and (3) changes in coupling between the various driver units and the ear canal. Changes in subject sensitivity are approximately 2 dB, independent of frequency, up to at least 13 kHz. Probe coupling changes are small below 9 kHz. At the higher frequencies, driver coupling changes are occasionally very large (more than 20 dB in extreme cases), generally much greater than changes in subject sensitivity, and dependent on frequency in a distinctive manner related to the geometry of the sound field.
Monaural Detection with Contralateral Cue (MDCC). I. Better than Energy Detector Performance by Human Observers
Authors: Taylor M. M. , Forbes S. M.
Published: October 2005

Human observers were given a monaural detection task. Information in the form of a “cue” derived in some manner from the signal was presented simultaneously to the other ear. The signal and the cue always had the same timing and spectral characteristics and were samples of low-pass filtered noise. The cue was always presented in each possible signal interval, whether or not the signal itself was presented. Different cue conditions were used, in which the cue bore different amounts of information relevant to the signal. When the cue and signal were independently generated but identically timed and filtered, performance was indistinguishable from the no-cue control condition, and was like that of an inefficient energy detector using a filter matched to the signal bandwidth. When the cue was an identical replica of the signal, performance was much better than that of an ideal energy detector and, for bandwidths less than 1600 Hz, approached that of an equally inefficient likelihood-ratio detector for signal known exactly. Efficiency in both cases was of the order of 25%–30%. When the cue was derived from the signal but passed through a wide-band 90° phase shifter, it provided an intermediate amount of information, and detection performance was also at an intermediate level. The results are taken to show that when relevant information is available to the detection mechanism, it can be used; and that the usual finding of energy-detector like monaural performance is due to lack of more precise information about the signal at the detector.
Free-Field Calibration of Earphones
Authors: Villchur Edgar
Published: October 2005

Probe-microphone measurements of the real-ear response of an earphone are subject to inherent problems of interpretation. The cushion-enclosed sound field is homogeneous only in the frequency region below 1 kHz, and measurements outside this band can differ by more than 15 dB from one probe position to another. Probe measurements at the earphone diaphragm do not provide enough information on earphone response, because the earphone can create or modify resonances in the outer ear that affect the pressure delivered to the eardrum. Measurements at the canal entrance provide too much information, because they include pinna gain characteristics that are not functions of earphone performance. In the present experiments, the response of an earphone is derived by subtracting, from earphone-induced sound pressures at the eardrum, the sound pressures produced at the same point by a loudspeaker that the pinna faces. The speaker is used to establish a reference of outer ear acoustic gain before disturbance by the earphone, less the effects of head diffraction. The eardrum position was selected for the probe-tube measurements after a preliminary experiment showed that a supraaural earphone can affect ear canal gain by constricting the canal entrance and lowering the canal's resonant frequency. The derived response curves were in agreement with earphone frequency-response data derived from subjective judgments by the corresponding subjects.
Loudness Judgments of Speech and Nonspeech Stimuli
Authors: Mendel Maurice I. , Sussman Harvey M. , Merson Richard M. , Naeser Margaret Ann , Minifie Fred D.
Published: October 2005

Listener's numerical estimations of loudness were compared for three sets of stimuli. The exponential loudness values for machine-generated signals varied from 0.80 to 0.86. The loudness functions for various speech conditions, recorded at normal effort levels and played back at seven different sound-pressure levels, varied from 0.74 to 0.84. The loudness functions of autophonically varied speech levels ranged from 0.86 to 1.20. Listeners in this study tented to respond differently to speaker-varied speech signal levels than to the electronically varied speech signals. Therefore, it is assumed that listener loudness judgments of speaker-varied speech levels are related to acoustic cues that vary as a function of amount of effort used by the speaker.
Perception of Vocoder Speech Processed by Pattern Matching
Authors: Smith Caldwell P.
Published: October 2005

Tests were conducted to assess speech discriminability with spectrum data from a channel vocoder compressed to values from 450 to 600 bits/sec by spectrum pattern matching, in comparison with speech discriminability for the same system operating with conventional pulse code modulation to encode spectrum data at rates from 900 to 2700 bits/sec. The pattern-matching method, in which each spectrum sample was processed by selecting and substituting a nearest neighbor pattern from a fixed digital memory, was tested in 12 configurations, ranging from 497 patterns (328 voiced, 169 unvoiced) to 3996 patterns (2893 voiced, 1103 unvoiced) with input speech consisting of recordings of eight scramblings of the 448-word diagnostic rhyme test described by Voiers. Tests with listening crews confirmed that pattern matching compares favorably with conventional 2400 bits/sec vocoder art in terms of consonant discriminability, with mean scores obtained with the 12 configurations of the pattern memory table as follows: sibilation, 97.9; nasality 95.1; compactness 93.0; voicing 88.4; graveness 86.7; sustention 67.0. The six features showed varying degrees of sensitivity to the composition and number of stored patterns. Total intelligibility scores ranged from 82.6 (using a total of 497 patterns and monotone pitch) up to 91.9 (using 3996 patterns and normal pitch at 300 bits/sec). Comparative data were plotted for feature discriminability versus spectrum data rate for pattern matching and for conventional pulse-code modulation.
Acoustico-Lateralis System of Fishes: Tests of Pressure and Particle-Velocity Sensitivity in Grunts, Haemulon sciurus and Haemulon parrai
Authors: Cahn Phyllis H. , Siler William , Wodinsky Jerome
Published: October 2005

Avoidance-conditioning studies on young grunts, the bluestriped Haemulon sciurus, and the sailor's choice, H. parrai, were carried out in a calibrated tubular plexiglas vessel, where the fish were subjected to either farfield conditions of sound, where sound pressure and particle velocity were equal, or to a nearfield situation, where the velocity exceeded the pressure by up to 35 dB. At 400 Hz, the fish were found to be sensitive to pressure only, at threshold levels. At 200 and 100 Hz, the threshold patterns were more complex, and the fish responded to either pressure or velocity irrespective of a near- or farfield pressure-velocity relationship, but probably dependent on previous conditioning and starting intensities. Our data suggest that as frequency is lowered, velocity sensitivity increases, and there appears to be a weak coupling of the pressure- and velocity-detection systems. This weak coupling is surprising view of the close relationship between the ear and the lateral-line sensory systems, the two receptors here involved. Studies are in progress to learn more about the various aspects of the low-frequency response.
Some Parameters Influencing the Perceptibility of Pitch
Authors: Bilsen Frans A. , Ritsma Roelof J.
Published: October 2005

A sound signal added to its repetition after a delay time τ is able to produce a pitch, repetition pitch, corresponding to 1/τ. When the repetition is attenuated relative to the original sound, the strength of the pitch sensation (the perceptibility of pitch) decreases. For white noise with its attenuated repetition and for sequences of pulse pairs with each second pulse attenuated, the threshold of perceptibility of pitch has been determined as a function of the pulse-pair interval T̄, the sensation level (SL), the bandpass center frequency f0, and the delay time (pulse interval) τ. The following conclusions can be drawn: (a) Somewhere in the hearing organ, timing information is preserved, rather perfectly, by means of some kind of autocorrelation process; (b) Above a certain minimum SL, the perceptibility of pitch is independent of the sensation level; (c) Dependent on the frequency value of the pitch, there is a specific spectral region for which the perceptibility of pitch is at a maximum; (d) The threshold as a function of f0 and τ shows a conformity between the existence region of repetition pitch and the existence region of the tonal residue.
Binaural Masking of a Tone by a Tone Plus Noise
Authors: Canahl Julius A.
Published: October 2005

Many investigators have indicated that release from masking does not occur for tone-on-tone masking. From this statement, it was hypothesized that the release from masking observed when noise is masking a tone signal would be affected by the addition of a tone masker. If the level of the tone masker is increased to a high enough value, there should be no release from masking. The results of the study showed that a pure-tone masker does reduce the size of the magnitude of the release from masking as a function of the level of the masking tone, but not to zero as was predicted. The effect was found to be differential with respect to the phase of the tone masker and is explained in terms of the interaural correlation of the total masker waveform. Some evidence is presented that indicates release from masking occurs when a tone is used to mask another tone.
Cooperation of Listener and Computer in a Recognition Task: Effects of Listener Reliability
Authors: Corcoran D. W. J. , Dennett J. L. , Carpenter A.
Published: October 2005

The purposes of the experiments were (a) to evaluate the influence of a computer display on the ability of listeners to recognize complex sounds, (b) to determine what effect variations in audio signal-to-noise (S/N) ratio would have on combined performance, and (c) to discover the strategy used by the listener to combine the computer with audio evidence. Thirty-three Naval Ratings were tested over twelve 112-h sessions. In the scored sessions, listening performance, computer performance, and listener-plus-computer performance (C & Li) were assessed. It was found: (1) that the computer display was effective in producing better recognition; (2) that the higher the S/N ratio, the greater C & Li performance; (3) that the lower the S/N ratio, the greater the utilization of the computer information; (4) that the utilization of the computer evidence did not improve with training; and (5) that a relatively simple additive model described the method by which the listeners combined the two sources of evidence.
Cochlear Innervation, Signal Processing, and their Relation to Auditory Time-Intensity Effects
Authors: Lynn P. A. , Sayers B. McA.
Published: October 2005

The detailed nature of the cochlear neural transduction process has been explored with the aid of new digital computer models that include features of known synaptic mechanisms and with the aid of recent data on cochlear neuroanatomy. The essential interest of this work is in the complex interactions between time and intensity observed both in binaural listening experiments with the human and in neural responses in the cat's auditory nerve. The results of these studies suggest the importance of the cochlear-innervation scheme for an understanding of cochlear signal processing; in particular, it has been shown that an interaction between afferent fibers associated with inner and outer hair cells could account for the major time-intensity effects discussed.
Binaural Fusion: Its Limits as Defined by Signal Duration and Signal Onset
Authors: Perrott David R. , Briggs Renee , Perrott Sharon
Published: October 2005

The results of two experiments on the interaural frequency limits for binaural fusion indicate that (1) the limits for binaural fusion decrease as a direct function of signal duration for both low- and high-frequency sine waves, and (2) signal onset is a significant factor in the determination of the spectral limits for binaural fusion only for high-frequency sine waves and low-frequency sine waves of short duration. In general, these results are consistent with a model of binaural interaction in which fusion is determined by a tonotopically organized mechanism, fusion being the product of binaural activity in a channel of limited bandwidth.
Pitch as a Voicing Cue
Authors: Haggard Mark , Ambler Stephen , Callow Mo
Published: October 2005

The pitch change at the onset of voicing after a period of articulatory closure for a consonant reflects the state of the glottis during that closure. In initial position, a low rising pitch indicates a closed glottis and high falling pitch a glottis that is still partly open. An experiment is reported which shows that, for about 90% of the subjects, this pitch change in the vowel can cue the voiced/voiceless distinction for a preceding stop consonant in English. Control conditions suggest that this cue depends not upon low-frequency energy content, but upon the pitch sensation.
Regulation of Voice Communication by Sensory Dynamics
Authors: Lane Harlan , Tranel Bernard , Sisson Cyrus
Published: October 2005

People speak more loudly in a noisy room or when momentarily deafened and more softly in a quiet room or when sidetone is artificially increased. The effort to compensate for these changes in the signal-to-noise ratio, or to match directly changes in the intensity of a model, typically falls about halfway short (in decibel units). This is probably because a speaker considers that he has doubled his own vocal level in half as many decibels as it takes to double the loudness of the signal or the noise. More concisely, the Lombard-reflex, sidetone-penalty and cross-modality matching functions have exponents of about one-half because the exponent of the loudness scale is half that of the autophonic scale of voice level. This amounts to saying that the speaker matches changes in signal or in noise to keep the signal-to-noise ratio nearly constant, but he is misled by the disparity in the sensory operating characteristics of speaking and listening.
Time Sharing in Auditory Perception: Effect of Stimulus Duration
Authors: Moray Neville
Published: October 2005

Listeners heard trains of tone bursts dichotically, one ear receiving bursts of one frequency, the other bursts of another. Listeners were required to detect increments in intensity, which might occur in either ear separately or in both ears at the same moment. Increasing the duration of the tone bursts was found to improve single-channel detectability in the classical way but to have relatively little effect on the detection of simultaneous targets.
A Nonparametric Detector for a Narrow-Band Signal
Authors: Shapiro Arthur
Published: October 2005

In 1962, Bryn derived the optimal processor for detecting a Gaussian signal in Gaussian noise with a three-dimensional array. Unfortunately, knowledge of the cross-spectral-density-function matrices for both the signal and the noise must be known before the detector can be implemented. Consideration of the optimal processor for narrow-band processes received on two units leads to the derivation of a detector that requires no a priori knowledge of the noise or signal characteristics, and that is significantly better than the standard detector when the noise is coherent. The direct extension of these results to larger arrays has thus far not been accomplished, but a simple application of the two-detector technique a uniformly spaced linear array indicates that even a rather crude innovation may achieve some improvement in detection.
Determination of the Elastic Constants of a Unidirectional Fiber Composite Using Ultrasonic Velocity Measurements
Authors: Zimmer J. E. , Cost James R.
Published: October 2005

Ultrasonic velocity measurements have been made to obtain the dynamic elastic stiffnesses necessary to determine fully the elastic properties of a unidirectional glass-reinforced epoxy-fiber composite. In units of 106 psi, these stiffnesses are C11=6.01, C22=C33=2.58, C12=C13=0.70, C23=1.42, and C44=0.49, where the subscript 1 refers to the fiber direction. Since more velocities were measured than were necessary to obtain the five constants required by the symmetry of this composite, the extra measurements were used to check on the experimental method. Analysis shows the ultrasonic technique to be satisfactory for measurement of the elastic stiffnesses of a fiber composite. The experimental results are compared with the elastic constants predicted for this composite from expressions based upon several theoretical models. Good agreement is obtained when the theoretical calculations are made using the dynamic (as opposed to the static) modulus of the epoxy matrix.
Propagation of Harmonic Waves in Composite Circular-Cylindrical Rods
Authors: Armenàkas Anthony E.
Published: October 2005

In this investigation, the general frequency equation for harmonic waves having an arbitrary number of circumferential nodes, traveling in composite traction-free, circular-cylindrical rods is established on the basis of the linear three-dimensional theory of elasticity. The composite rods consist of a circular core made of one material, bounded by and bonded to a circular casing of another material. Simpler degenerate cases of the frequency equation are reduced and discussed. A numerical evaluation of the frequency equation is presented. The results are obtained by programming an iteration procedure on a digital computer. The effect of the variation of the physical and geometric parameters of the rod on the frequencies and mode shapes of the first few modes is illustrated and discussed. Moreover, the feasibility of utilizing composite rods as delay media in guided-wave ultrasonic delay lines is considered briefly.
Optimum Damping and Stiffness in Nonlinear Single-Degree-of-Freedom Systems. I. Ground Acceleration Shock
Authors: Kemper John D. , Ayre Robert S.
Published: October 2005

The protection of a single-degree-of-freedom system from ground shock is examined; the shock is an acceleration pulse with a vertical front. The item to be protected is mounted on an isolator containing both nonlinear stiffness and nonlinear damping (exponentially “hardening” or exponentially “softening”). A large range of the system parameters and several values of pulse duration are examined, using a digital computer; a total of nearly 700 time-dependent solutions are involved. The results show that components possessing nonlinear stiffness and nonlinear damping can be used to significant advantage. If an allowable relative displacement specified, it appears that the peak absolute acceleration can be reduced as much as 40%; if an allowable absolute acceleration is specified, it appears that the peak relative displacement can be reduced as much as 30% to 40%. However, for small allowable displacements or for moderately large allowable accelerations, the results from nonlinear and linear systems are not significantly different. The smallest peak acceleration achieved by the nonlinear systems is 10% to 30% below the smallest peak acceleration of the linear systems, depending upon pulse duration. “Softening” damping functions proved to offer the greatest advantages, but the range of favorable stiffness functions included both “softening” and “hardening” types.
Optimum Damping and Stiffness in Nonlinear Single-Degree-of-Freedom Systems. II. Velocity Shock
Authors: Kemper John D. , Ayre Robert S.
Published: October 2005

Cases of landing impact (velocity shock), such as the dropping of a packaged item or the landing of an airplane or spacecraft, are investigated. The packaging material, or the shock-absorbing landing gear, is assumed to be nonlinear (exponentially “hardening” or exponentially “softening”) in both stiffness and damping. A large range of the system parameters is investigated, using a digital computer to solve the nonlinear differential equations, involving a total of about 500 individual time-dependent solutions. It is found that, for the range of parameters investigated, significant advantages are possible by using nonlinear systems, as compared to what can be achieved with purely linear systems. If an allowable displacement is specified, it appears that the peak acceleration can be reduced as much as 35%; with a given allowable acceleration, the peak displacement can be reduced as much as 25% to 30%. However, for moderately large allowable displacements or for small allowable accelerations, the results from nonlinear and linear systems are not significantly different.
Oscillatory Impact of an Inhomogeneous Viscoelastic Rod
Authors: Park Im K. , Reiss Edward L.
Published: October 2005

A stress is applied to the end of a semi-infinite, inhomogeneous, “standard” viscoelastic rod. The rod is initially unstressed and at rest. The applied stress is uniformly distributed over the end, and it is oscillatory in time. The propagation of small-amplitude, one-dimensional, longitudinal waves is studied. A formal asymptotic expansion of the solution is obtained. A partial justification of the method for homogeneous rods is given. The leading term in the expansion represents a modulated, oscillating, progressive wave that propagates with variable velocity. The modulation depends on the elastic and viscous moduli. The velocity depends only on the elastic moduli. The Maxwell rod is studied as a limiting case of the standard rod. Application of the method to finite rods is discussed.
Transient Analysis of Stress Waves around Cracks under Antiplane Strain
Authors: Ravera R. J. , Sih G. C.
Published: October 2005

This paper carries out a mathematical formulation of the antiplane strain problem of a crack with finite width subjected to any time-dependent loadings. It is based on integral tranforms and a technique employed originally by Cagniard and simplified subsequently by De Hoop in geophysical-layer problems. The procedure obviates the contour-integration difficulties and permits the explicit recovery of the transient result by insepction. An illustrative example is given for the case in which a finite crack suddenly appears in an elastic solid under anitplane shear. A Fredholm integral equation of the second kind is obtained in the Laplace transform domain and solved numerically on the computer. Asymptotic forms for the transient stresses near the crack tip are found and a dynamic stress-intensity factor, which is held important in the current theory of crack propagation, is defined. Numerical results showing that the transient stress reaches a peak very rapidly and then oscillates about the static value are displayed graphically.
Forced Vibration of Internally Damped Circular Plates with Supported and Free Boundaries
Authors: Snowdon J. C.
Published: October 2005

This paper considers the vibration response of circular plates that are driven at their midpoints by a sinusoidally varying point force. The plates have simply supported or free boundaries and are assumed to be internally damped. The corresponding solutions to the thin-plate wave equation are described. Because the solutions involve ordinary and modified Bessel functions of complex argument, methods for obtaining the real and the imaginary parts of these functions are described and their results compared. Expressions are derived for the driving-point and transfer impedances and for the force and displacement transmissibilities of the plates. Representative calculations showing the frequency dependence of these quantities for internal plate damping of the solid type are presented, and their physical significance is discussed. The effect of attaching lumped masses to the plates at their midpoints is also examined.
Sound Radiation from Rigid Flow Spoilers Correlated with Fluctuating Forces
Authors: Heller Hanno H. , Widnall Sheila E.
Published: October 2005

This paper presents the results of a theoretical and experimental study of the correlation of fluctuating forces on rigid flow spoilers with the resulting sound radiation. A system of force transducers was developed to measure simultaneously, yet independently, the drag and lift components of the fluctuating forces on flow spoilers confined within a jet-pipe system. A direct correlation of fluctuating forces with the radiated sound was found. A theory that considered the effect of the enclosure upon the sources and the effect of pipe-end reflection was developed to predict the sound power radiated to the free field from pipe-immersed flow spoilers. Both monopole and dipole sources were treated. An increase of the dipole sound-power output by a factor of 3 for frequencies below the pipe cutoff frequency was predicted and experimentally confirmed.
Third-Order Elastic Moduli of Cubic Crystals
Authors: Elkin S. , Alterovitz S. , Gerlich D.
Published: October 2005

The relations between the third-order elastic moduli and the “natural” velocity for pure-mode sound propagation and stress in the [111], [11̄0], and [112̄] directions in cubic crystals are derived. The advantages of determining the third-order elastic moduli from measurements in the latter directions are discussed.
Sound Speed in Pure Water and Sea Water
Authors: Del Grosso Vincent A.
Published: October 2005

New interferometric measurements of the speed of sound in pure water and standard sea water are presented, The pure-water results are reasonably consistent with other recent measurements while the sea-water results cast additional suspicion on the concept of salinity as a characterization of sea water.
Sampling Statistics for an Acoustic Mode
Authors: Waterhouse Richard
Published: October 2005

The distribution functions are considered for the random sampling in space of a three-dimensional acoustic mode. These functions are of interest when it is desired to estimate either the total acoustic energy present in the space, from a finite number of sample values, or the driving point impedance at an arbitrarily chosen point. Expressions are obtained for the probability density and cumulative functions for axial, tangential, and oblique modes set up in a rectangular space containing an ideal elastic fluid. The results are derived theoretically and checked by a numerical sampling procedure. It is found that the distributions are independent of the proportions of the enclosure and of the mode number. They are also the same for hard or soft boundary conditions, or for combinations of these.
BOND INSPECTION BY DYNAMIC TIME-AVERAGE INTERFEROMETRIC HOLOGRAPHY OF ULTRASONICALLY EXCITED PLATES
Authors: Erf Robert K. , Aas Herbert G. , Waters James P.
Published: October 2005

In thin plates, the visualization of ultrasonically excited plates modes by dynamic time-average interferometric holography can be used to detect some types of material defects. Representative results of a feasibility study, which dramatically demonstrate the potential of the method for nondestructive inspection of the bonds between boron-epoxy prepreg material and aluminum substrates, are presented. In particular, it is shown that an area of less than 1 cm2 can be easily identified with an excitation frequency on the order of 20–40 KHz.
EASY METHOD FOR MEASURING THE NATURAL FREQUENCY AND DAMPING RATIO OF ELECTROMAGNETIC SEISMIC VIBRATION PICK-UPS
Authors: Braun S.
Published: October 2005

A method is described for measuring the natural frequency and damping ratio of an electromagnetic seismic transducer. The method is purely electronic and is without any mechanical excitation.
Response of Neurons in the Cochlear Nuclei to Variations in Noise Bandwidth and to Tone-Noise Combinations
Authors: Greenwood Donald D. , Goldberg Jay M.
Published: October 2005

Experiments were performed in which bands of noise were widened (arithmetically) around the best frequencies of single units in the cochlear nuclear complex of the cat. Two types of effect that were noted earlier by Greenwood and Maruyama [J. Neurophysiol. 28, 863–892 (1965) and unpublished observations] were observed more precisely: (1) summation, in which increasing bandwidth from narrow widths (constant spectrum level) produced increases in firing and (2) “suppression,” in which increasing bandwidth beyond the range in which summation occurred produced systematic reductions in firing. In monotonic units, in which summation was more readily observed, increasing bandwidth was approximately equivalent to increasing the spectrum level of a narrow band of constant width; the subsequent suppression at larger bandwidths ranged from slight to very marked. The bandwidths at which summation ceased and suppression began decreased somewhat at higher spectrum levels and were similar in width on a log scale for units of differing best frequency but, for several reasons, these “turnover” bandwidths are not readily interpretable. Tone-noise-combination stimuli were also used to study some units, and it was possible to repeat and extend earlier observations by Greenwood and Maruyama to the effect that—depending on intensity—a band of noise centered at one frequency may eliminate, i.e., mask, a unit's response to a tone at a different frequency either (a) by inhibiting that response or (b) activating the unit itself so that the tone has no additional effect. These results are similar to recent observations of primary unit behavior.
Measurement of the Cochlear Potentials of the Guinea Pig at Constant Sound-Pressure Level at the Eardrum. I. Cochlear-Microphonic Amplitude and Phase
Authors: Laszlo C. A. , Gannon R. P. , Milsum J. H.
Published: October 2005

Accurate frequency-response data for the cochlear potentials of the guinea pig were required for the description of the electrical events in the inner ear in terms of a mathematical model. Previously used methods did not ensure constancy of the input stimulus to the ear, and it was, therefore, necessary to monitor the sinusoidal-input amplitude and phase at the eardrum. Simultaneously, the cochlear microphonic potential (CM) amplitude and phase were measured over the frequency range 100–10 000 Hz, with differential electrodes inserted in three turns of the guinea pig's cochlea. The CM-amplitude versus frequency curves showed a “tuning-curve” shape in general, but the exact shape of these curves was influenced by the location of the electrodes and the sound pressure level (SPL) used. The peak of the CM-amplitude versus frequency plots never appeared at frequencies higher than 2000 Hz owing to the “low-pass” characteristics of the middle ear. The CM-phase versus frequency plots showed increasing phase lag, but there was relatively slow increase of the measured phase delay in the basal turn. Both these observations and the CM-amplitude measurements indicated that the electrodes picked up the CM from many potential generators that were not excited in phase and that interference between the outputs of the individual hair-cell generators occurred.
Adaptation and Loudness Decrement: A Reconsideration
Authors: Petty Joseph W. , Fraser Winifred D. , Elliott Donald N.
Published: October 2005

The interpretation of data obtained with simultaneous dichotic loudness balance (SDLB) procedures as a reduction in the loudness response of the adapted ear to monaural stimulation is questioned. Since simultaneous homophonic presentation provides location cues as well as binaural loudness interaction cues, other interpretations than reduction in monaural loudness response are available. Further, the electrophysiological data cited to support the loudness-reduction interpretation bear little similarity to the typical SDLB adaptation curve. The method of delayed balance, in which it is possible to obtain relatively uncontaminated judgments of loudness in the adapted and comparison ears, has been utilized. With such a procedure, no evidence of loudness decrement was evident at exposure intervals from 1 sec to more than 7 min, for an exposure intensity of 60 dB SL. It is concluded that SDLB judgments reflect a conglomerate of imperfectly related cues whose potency may vary for different Ss and probably does vary for the same S during the adapting exposure.
Magnitude of Cochlear Microphonics Elicited by Components of Broad-Band Noise
Authors: Mainen Michael W. , Chiong Vicente T. , Glackin Robert N. , Elder James C. , Warfield Dickens
Published: October 2005

Cochlear microphonics from the round window of cats were studied when the stimulating frequency was a pure tone and when the frequency was a component of a band of noise. The sound pressure level (SPL) of the frequencies were equated under both conditions. Input frequency components of noise and corresponding output voltages were measured with a 3-cycle wave analyzer and corrected to a 1-cycle bandwidth. Eight frequencies were employed, each at several intensity levels up to the point of overloading. Measurements were made on five cats in which the ipsilateral eighth nerve had been completely sectioned 74–78 h earlier, and on 10 cats in which the nerve was intact. The same results were obtained with intact and sectioned nerves: the cochlear output to pure tines was in general greater than to identical frequency components of noise at equal intensities. The tone-to-noise output ratio increased with increasing intensity. Overloading occurred at much lower SPLs for frequency components of noise, the differences being as great as 50 dB. These phenomena are attributed to processes occurring within the cochlea prior to central influences. Nerve section was verified by absence of tunnel fibers and nerve action potentials.
Plane-Wave Tube for Low-Audio-Frequency and Infrasonic Acoustic Measurements
Authors: Brouns Austin J.
Published: October 2005

A plane-wave tube has been designed to measure microphone frequency response and polar response at frequencies as low as 1 Hz. The acoustic impedance presented at the end of an open pipe becomes vanishingly small as frequency decreases. Consequently, a planar cover set at the end of the pipe, having a specific acoustic resistance of ρc, provides the required nonreflecting termination. The cover is fabricated of layers of cloth sandwiched between aluminum honeycomb. The upper frequency limit for general polar-response measurements is determined approximately where λ equals 10 tube diameters. The lower frequency limit is determined only by microphone sensitivity and speaker response. A 10-ft-long by 30-in.-diam tube was built, using four large woofers as sound sources, with a 35-Hz upper frequency limit. Excellent polar responses of a cardioid microphone were measured at 1 Hz. Careful measurements were required to adjust the termination resistance to ρc.
Simple Measurement Technique for Small Relative Velocity Changes of Gigahertz Acoustic Waves
Authors: Edgerton Robert F.
Published: October 2005

A simple method for measuring small relative acoustic velocity changes of gigahertz acoustic waves over a temperature range from 1.7° to 50°K has been developed. It has been possible to extend the conventional pulse-echo method to the gigahertz frequency range by displaying the intermediate frequency (60 MHz) on an oscilloscope and recording the changes in the phase of the i.f. associated with a chosen echo as a function of temperature. Using a Tektronix 454 oscilloscope sweeping at 5 nsec/cm, a precision of about 10 ppm can be achieved. Results on KCl:Li+ and KCl:CN− illustrate the usefulness of the technique.
Efficiencies in the Exchange of Translational and Vibrational Energies in Cyclopropane-Argon Mixtures
Authors: Welsh Alan G. , Taylor Jay E.
Published: October 2005

The velocity dispersions in cyclopropane-argon mixtures are investigated as a means of characterizing the repulsive parameters both for cyclopropane and argon. It is found that the removal of energy from a vibrationally excited cyclopropane is more efficiently accomplished by another cyclopropane molecule than by an argon atom. Since there is virtually no mass effect in comparing the probabilities of translation-vibration energy exchange for cyclopropane-argon and cyclopropane-cyclopropane encounters, the difference is attributed to a steeper intermolecular potential in the case of cylcopropane self-collisions. Quantitative results are obtained by comparing the experimental values with those from the equation of Herzfeld and Litovitz.
Asymptotic Analysis of the Modes of Wave Propagation in a Solid Cylinder
Authors: Achenbach J. D. , Fang S. J.
Published: October 2005

An asymptotic method is used to analyze the free vibrations of a solid elastic cylinder of circular cross section. In this method, the displacement components and the frequencies are sought as power series of the dimensionless wavenumber ε, where ε = 2π × RADIUS/WAVELENGTH. By substituting the expansions in the displacement equations of motion and the boundary conditions, and by collecting terms of the same order εn, a system of coupled second-order inhomogeneous ordinary differential equations is obtained with the radial variable as independent variable. Subsequent integration yields the coefficients of εn for the displacement components and the frequencies for all modes and for the whole range of frequencies, but in a range of real-valued dimensionless wavenumbers 0 < ε < 1.
Multipath Reflections from a Random Surface
Authors: Martin John J.
Published: October 2005

A method for counting the expected number of multipath reflections from a random surface between a source with finite beamwidth and a target or receiver is presented. The analysis is carried out for both one- and two-dimensional roughness and for multiple bounces between grossly parallel boundaries of the transmitting medium. As asides, a comparison is made between theoretical results and a graphical experiment, and a computer methodology for the case of linear phase velocity gradient is presented. The results of this paper could be useful in estimating numbers of multipaths for transmissions between earthbound or airborne high-frequency radio source and receiver via earth and/or electron overdense ionosphere; between underwater sound source and receiver via ocean bottom and surface; and, in curvilinear coordinates, between earth station and space station via moon surface.
Vibrations of Elastic Surface Systems Carrying Dynamic Elements
Authors: Jacquot R. G. , Soedel W.
Published: October 2005

The set of problems where shells, plates, or membranes carry discrete dynamic systems at discrete points on their surface is treated in a general manner. Interaction of each discrete dynamic system with the surface system is assumed to be in direction of the normal to the surface only. General solution equations are given. To apply these general equations to a specific problem, the eigenfunctions and eigenvalues of the surface system alone and the displacement impedances of the discrete dynamic systems at their point of attachment are required. The eigenfunction and eigenvalue equations of a system consisting of a circular cylindrical shell carrying a dynamic absorber, which is also connected with a second spring to ground, are obtained as specific examples.
Vibration of an Aelotropic Spherical Shell
Authors: Ramakrishnan C. V. , Shah A. H.
Published: October 2005

In this paper, a separable homogeneous solution for the displacements and stresses in a freely vibrating deep spherical shell exhibiting spherical isotropy is derived. A six-mode shell theory is proposed that includes the effects of shear deformation, rotary inertia, and transverse normal strain. The frequency spectra, corresponding to three different materials with varying degrees of anisotropy, are analyzed for two values of thickness-to-mean-radius ratios. Also, open spherical shells under various boundary conditions are investigated and mode shapes are studied.
In-Plane Transient Response of a Sandwich Ring to Radial Impact
Authors: Sagartz M. J. , Keer L. M. , Herrmann G.
Published: October 2005

The transient response of sandwich rings to concentrated radial impulsive loads is studied on the basis of a Timoshenko-type theory. Solutions are obtained by integral transform techniques and also by representation in series of normal modes. Numerical results show that the ring's response is predominantly flexural and is highly dependent on the ratio of the extensional stiffness to the shear stiffness. It is also found that as the core stiffness decreases relative to the facing-sheet stiffnesses, the influence of the thickness-to-radius ratio becomes more important.
Existence and Stability of Periodic Motions of a Harmonically Forced Impacting System
Authors: Senator M.
Published: October 2005

A simple idealization of a vibratory plow, which is impacting against an immovable relatively rigid obstruction, is analyzed to determine possible periodic motions and the stability of these motions. The plow is idealized as a translating rigid body with an applied harmonic force and viscous damping. It is pushed against a wall by an applied bias force, with the resulting impacts characterized by a coefficient of restitution. Necessary conditions are found for the existence of periodic motions with one impact per motion cycle. The infinitesimal stability of these periodic motions is investigated, and it is found that either a motion with the highest number of crank revolutions per cycle is stable or none are stable. Some cases are investigated numerically, and it is found that the infinitesimally stable solutions are approached even for large departures from the periodic initial conditions. For unstable cases, the two dependent variables of greatest interest, average number of force cycles per impact and average impact velocity, can be approximated by using the formulas developed for the one-impact-per-cycle motions analyzed.
Zero-Crossing Shift as a Detection Method
Authors: Bom N. , Conoly B. W.
Published: October 2005

Rice first showed the theoretical relationship between the expected number of zero crossings over a unit time interval and the spectrum of stationary Gaussian random noise. If an additional signal causes the spectral content to change, then the number of zero crossings may change. It is the purpose of this paper to familiarize the reader with the recognition of the change in the zero-crossing rate as a possible detection method. The principle of the effect is illustrated by two examples, one using a simple artificial noise mixture and the other using a noise recording made at sea. Subsequently, the statistical properties of the zero-crossing rate and an appropriate detection criterion are discussed.
Dependence of Spatial and Temporal Correlation of Forward-Scattered Underwater Sound on the Surface Statistics. I. Theory
Authors: Clay C. S. , Medwin H.
Published: October 2005

The correlation of underwater sound forward scattered from a time-varying statistically rough surface has been studied for the low-roughness case. The surface was illuminated by a divergent sound beam. Directionality of the source and receivers was included in a surface-illumination function. As an alternative to solving the Fresnel integral, the illuminated area was divided into subareas, for which the plane-wave Helmholtz-Kirchhoff treatment was valid. We used the criterion that the wavefront should be within λ/8 of the plane tangent to the wavefront over the subarea. The sound signals reflected and scattered at each subarea were separated into coherent and incoherent components, and the coherent components from the subareas were added coherently. The covariance of signals observed at a pair of receivers was computed with the aid of the bivariate Gaussian distribution function. Computations of the sound scattered by a traveling roughness, such as a gravity wave, showed that the covariance of the signals scattered into the first receiver and later into a second receiver can be large at a time delay, which is related to the group velocity of the roughness. The temporal and spatial covariances were also computed for a surface roughness having a damped cosinusoidal dependence upon space and time. The main contributions to the modulations of the spatial or temporal covariances came from the sound that was scattered from the subareas in nonspecular directions.