bluuebunny/crossref_metadata_2025 huggingface dataset:
Orientation to Speech Sound
Authors: Myers T. F. , Zhukova R. , Chistovich L. A.
Published: October 2005

A series of experiments are described in support of a model of speech recognition. The vowel /a/ from a complex signal generator was presented binaurally, each ear channel being independently controlled for signal intensity and duration of a medial silent interval (0–90 msec), such that a fused percent /a/, /ara/, /ala/, or /a-a/ resulted in the center, or to one or other side of auditory space. Analysis of categorical response probability and lateralization of a percept as functions of duration of the interval and interaural intensity difference enabled the functional levels and operations represented by the model to be substantiated.
Spoken Digit Recognition Using Partial Autocorrelation Coefficients (PAC)
Authors: Nakano Y. , Ichikawa A. , Nakata K.
Published: October 2005

Spoken digit recognition using autocorrelation coefficients (PAC or k parameters) is investigated with a digital computer. Speech samples are 10 spoken Japanese digits uttered by a single male speaker. Each digit is uttered 10 times. Each sample is analyzed at every 10 msec to give time series of PAC. Principle of recognition is a simple pattern matching with nonlinear time adjustment by DP procedure. When the dimension of PAC is greater than 4, recognition score is fairly good, but does not exceed the value of 98%. The cause of error seems to be the accuracy deterioration of computation of PAC. The computation of PAC is strongly correlated to a signal amplitude. Weighting PAC by amplitude information, the recognition score is improved and reaches at 100%, with the dimension of PAC greater than 4. When PAC is computed by fixed-point arithmetic with short accumulator length, the score become worse with the increase of the dimension. Further improvement of recognition score and time is expected by the variable use of PAC dimension controlled by the computation accuracy.
Analysis of Nasal Consonants
Authors: Fant G. , Erikson Ylva
Published: October 2005

Spectral analysis has been made of 12 Swedish speakers' nasal consonants /m/ and /n/ followed by four different vowels. Typical patterns of nasal murmur and assimilated nasality in the vowel portion are discussed with respect to established pole-zero models and results from earlier studies including sweep frequency measurements of the vocal and nasal tract. The perceptual significance of various pattern aspects are discussed.
The Effect of Nasal Oral-Cavity Uncoupling on the Sound Levels of Selected Stimuli
Authors: Zimmerman R. L. , Hoshiko M.
Published: October 2005

Sound level measurements of five selected narrow-band noises 30-Hz wide (center frequencies at 250, 730, 1090, and 2440 Hz and 4 kHz) and two pure tones (250 and 500 Hz) were made at the external aperture of the left nostril of each of 12 trained male subjects. A miniature transducer, positioned in the oral cavity of the subjects was used for stimulus presentation. Measurements were made during each of two subject generated physiological states. The first measurement was made when the subject's oral and nasal cavities were in open communication. A second measurement was made with the two cavities separated through velopharyngeal sphincter action. The recorded sound levels for the two conditions for all stimuli were statistically compared. The narrow-band noise with the center frequency at 250 Hz and the 250-Hz pure tone were found to be statistically different from the other stimuli. In all significant comparisons, the difference values were shown to be indicative of less attenuation of the 250-Hz narrow-band stimulus and of the 250-Hz pure-tone stimulus.
Dimensional Analysis of a Full Vowel Set
Authors: Wright R. D.
Published: October 2005

Previous investigators (Li et al.; Pols et al.; Singh; Watanabe; Wright and Boehm) have reported on the dimensional analysis of sets of Dutch and English vowels. The present investigation used a vowel set larger than that available in any of the single-language sets previously analyzed. The vowel set used contained all combinations of high-low, back-front, and rounded-unrounded distinctions. Representative spectra were measured for twenty-two vowels and analyzed for principal components. The resulting dimensions of maximum variance are compared to the previously reported physical and perceptual dimensions for vowel sounds.
Analysis of Tongue Parameters for Vowels
Authors: Rice Lloyd
Published: October 2005

A computer system is described that will accept a spoken vowel as input and then adjust the area function of a vocal-tract synthesizer to duplicate the input vowel quality as nearly as possible. The synthesizer output is matched against the input vowel spectrum using the Markel inverse filtering system. The program allows the definition of alternative parameter models for controlling the vocal-tract area function and represents a preliminary attempt to simulate the major vocal articulators. Each of three to six parameters is defined in terms of its contribution to the movement of each of the 18 sections used in the line analog synthesizer. Thus, the action of parameter Pi is defined by the 18-element vector of weights Wi1, Wi2, ⋯, Wi18. Any vocal tract shape within the range of the model is specified by assigning the appropriate value Pi to each of the parameters. The deflection of the jth section away from the neutral tract position is then given by the sum of products P1W1j+P2W2j+P3W3j+⋯. Various parameter models will be explored to determine their usefulness in providing unique and reasonable tongue shape descriptions.
More Visible Speech
Authors: Baker Janet M. , Baker James K. , Lettvin Jerome Y.
Published: October 2005

This paper presents a method for visual display of acoustical waveforms with which different phonemes are more readily distinguished than with spectrograms. The visual display is based on the interval between successive up crossings of the zero axis in the waveform. Although zero crossings and tip crossings have been used by several investigators since Licklinder's studies demonstrating that zero-crossing information is sufficient for intelligibility of speech, most investigators have ignored an essential property of up-crossing analysis. Analysis of up crossings is a time domain technique and as such, allows a perfect resolution of events in time, a resolution which is lost if the up-crossing data is averaged over intervals of time. Such precise time resolution is critical for the recognition of certain distinguishing features in various consonants. These features permit a visual display in which the phonemes can easily be distinguished, even in connected speech. Furthermore, the important features for discriminating among the consonants are highly speaker invariant.
A Factor Analysis of Competing Message Testing in Hearing Aid Evaluations
Authors: Bode Daniel L. , Dodds Elizabeth F. , Carhart Raymond
Published: October 2005

Retrospective data compiled from routine clinical hearing aid evaluations were examined to identify the primary factors influencing test performance of hearing-impaired listeners. Results were analyzed from representative and similarly conducted evaluations with 68 patients. Unaided test measurements were obtained bilaterally, and included pure-tone thresholds, slope of the audiometric contour, speech reception thresholds (SRT), and speech discrimination scores. Aided tests included speech reception threshold, speech discrimination in quiet, and speech discrimination against a competing message. When intercorrelations among 27 test variables were subjected to factor analysis, five factors emerged: speech discrimination, nontest ear thresholds, unaided sensitivity-test ear, interear high frequency thresholds, and aided SRT. The 68 sets of data were subdivided into two groups on the basis of severity of hearing impairment, and new factor analysis were run. Here the same array of factors emerged with the addition of (1) a nontest ear high-frequency factor for the milder loss subgroup and (2) two factors designated as SRT—poorest aided performance, and discrimination—poorest aided performance for the greater loss subgroup.
Discrimination Loss and Masking by Low-Frequency Vowel Formants
Authors: Martin E. , Osberger M. J. , Pickett J. M.
Published: October 2005

Most persons with sensorineural hearing loss have some impairment of speech discrimination ability. In most cases, discrimination of consonants is poorer than discrimination of vowels. This study investigates the ability of hearing-impaired Ss to discriminate one type of consonant cue—a vowel formant transition. Our purpose was to study the effect of the presence of F1 on discrimination of F2 transitions. The test stimuli were synthetic vowels whose spectra approximated those of [a]; [i]; they were 250 msec in duration. When an F2 transition was presented, it occurred over the initial 100 msec, after which F2 did not change. The Ss were 23 persons with moderate to severe sensorineural hearing loss and four normal-hearing persons. Results: Some hearing-imparied Ss showed essentially normal discrimination with F1 present. However, in most of the Ss, F1 produced large amounts of masking in both [a] and [i]. The amount of masking was greater in [i] than in [a]. In this respect, the effect is not the same as the “classical” upward spread of masking. When the normal Ss were tested at sound levels approximating those used to test the hearing-impaired Ss, they showed large amounts of masking. The high sound levels at which hearing-imparied persons must listen appear to be a factor in their discrimination loss. [Work supported partly by the U. S. Public Health Service.]
Speech Feature Perception by Listeners with Severe Sensorineural Hearing Loss
Authors: Pickett J. M. , Martin Ellen S.
Published: October 2005

How well do persons who show discrimination loss for speech perceive the different phonetic features, i.e., consonant voicing, place and manner of articulation, and vowel features? Would the pattern of feature perception be radically different between groups of listeners with different amounts and frequency contours of hearing loss? We present preliminary answers to these questions based on group confusion matrices of the responses to a speech perception test given to 99 impaired listeners. Results show that the feature of place of consonant articulation is heard more poorly than the features of voicing and low-frequency continuance, over a rather wide range of listener groups. Groups formed according to frequency contour of hearing loss showed some significant, but relatively small, differences in feature reception.
A New System for Performing Sensorineural Acuity Level (SAL) Testing
Authors: Yates James T.
Published: October 2005

A system for SAL testing has been developed which alleviates the problems previously experienced with SAL-Rainville procedures. The occlusion effect, the primary problem area in SAL testing, was circumvented through the design of a non-occluding earphone which incorporated an especially constructed miniature transducer. The use of a narrow-band masking effectively extended the useful range of the SAL procedure. The system is now in limited clinical and research application.
Pure-Tone Masking in Normal and Cochlear Impaired Ears
Authors: Richards Alan M.
Published: October 2005

Pure-tone masking patterns were obtained using equivalent sensation levels (SLs) of a 500-Hz masking tone in both normal hearing and cochlear impaired subjects. When the level of the masker was set at a relatively low intensity (35 dB SL), the two groups yielded equivalent threshold shifts at all of the masked frequencies (125–8000 Hz in octave increments). However, when the masker level was increased to 55 dB SL, it was found that those cochlear impaired subjects who exhibited particular audiometric criteria below 2000 Hz (e.g., 20 dB HL threshold at 500 Hz) generally showed greater threshold shifts at 1000 and 2000 Hz, while those impaired subjects not meeting these criteria yielded masking patterns that differed in no essential manner from the normals. These results were evaluated relative to those studies that have used narrow-band noise to investigate the spread of masking phenomena in normal and pathological ears.
Effects of Testing Methods on Békésy Thresholds
Authors: Young I. M.
Published: October 2005

Thresholds and amplitude measurements of fixed-frequency Békésy tracings were made for continuous tones using the method of adjustment on normal hearing subjects. Attenuation rates were 1, 2, 4, and 8 dB/sec with 0.2 dB steps. Results indicated that while the thresholds measured at the midpoints of amplitudes were practically constant with differ-attenuation rates, the thresholds at the tops and the bottoms of amplitudes showed a distinct difference for changing attenuation rates. As attenuation rates increased, the thresholds at the tops of amplituded improved and the thresholds at the bottoms of amplitudes became worse. Amplitudes increased in size as attenuation rate increased but there was no constant correlation between amplitude and attenuation rate. Conventionally, the midpoint of the Békséy amplitude has been considered the best estimate of the threshold. This is true only when the Békésy audiogram was obtained by using the method of adjustment.
Auditory Thresholds using a Single Sweep Frequency Modulation
Authors: Young I. M. , Wenner C.
Published: October 2005

Békésy thresholds were obtained for frequency-modulated tones in normal-hearing subjects. Measurements were made at a fundamental frequeucy of 1000 Hz by using combination of four frequency deviations, four “on times,” and three “off times.” In each case, the on time consisted of a single sweep of frequencies. Attenuation rate of Békésy-type recording attenuator was 1 dB/sec. Results indicated that for a given frequency deviation, the thresholds improved with longer on time (slow sweep of frequencies) and longer off times. For a given on timne, as frequency deviation increased the threshold improved. Combination of long on time, long off time, and wide frequency deviation resulted in the best threshold.
Sound Pressure Transformation from the Free Field to the Eardrum
Authors: Shaw E. A. G.
Published: October 2005

The sound pressure transformation by the human head and external ear has been the subject of many measurements over a long period of time. The average acoustic properties of the external ear are now established sufficiently well that diverse data can be brought into a common set of reference frames. Data from 10 studies in five countries are presented in terms of eardrum response at eight azimuthal angles as functions of frequency from 0.2 to 12 kHz. Data from the same pool are also presented in terms of azimuthal variations and interaural level differences at 18 frequencies. Where there is lack of agreement between studies, the presentation often indicates the probable causes. A critical examination of all the data leads to self-consistent families of average response at the eardrum position as a function of frequency and angle of incidence in the azimuthal plane. An extension of the method should provide useful estimates of average response at angles of incidence not on the horizontal plane.
Aural Noise as a Function of the Cardiac Cycle
Authors: Soderquist D. R. , Lindsey J. W. , Harter M. R.
Published: October 2005

Investigators have suggested several internal noises that affect absolute thresholds (e.g., heart sounds, circulatory pulsations, muscle tremors). Furthermore, it has been suggested that blood flow may modulate aural noise in the external canal. Since mental blood vessels cannot expand outward due to bone encasing the canal, an inward expansion is suggested which induces an increase in aural noise by decreasing mental volume under the earphone. In short, the meatal pulsation hypothesis (MPH) suggests a modulation of aural noise as a function of blood flow through the ear canal. This study examines the MPH under three conditions (tight and normal fitting supraaural cushions and an insert earmold) as a function of the cardiac cycle. Three dependent measures were obtained, viz., EKG, blood flow at the earlobe, and pressure changes within the ear canal (positive pressure indicating, according to the MPH, an inward expansion of the blood vessels). The EKG R-wave keyed a signal averaging computer which in turn averaged the data over 32 separate heartbeats. Results indicate: (1) a maximum positive pressure approximately 225–250 msec after the R-wave with rapid decreases prior to and immediately after the maximum (tight fitting earphones); (2) no systematic pressure change with normally fitting earphones; (3) an inverse relationship between blood flow at the earlobe and pressure change within the meatus. The maximum negative pressure occurring near 225–250 msec after the R-wave.
Anatomical Correlates of a Temporary Shift in the Threshold of Hearing
Authors: Bohne B. A.
Published: October 2005

When chinchillas are continuously exposed for more than 24 h to an octave band of noise centered at 500 Hz, the behavioral TTS for 715-Hz tone stabilizes at an asymptotic value proportional to band level [Carder and Miller, Trans. Amer. Acad. Ophthal. Otolaryng. 75, 1346 (1971)]. Recovery to normal thresholds requires from two to seven days. Chinchillas were exposed to this same noise for two days at 65, 75, 85, or 95 dB SPL. The organ of Corti was immediately fixed and prepared as a flat, whole-mount specimen in plastic suitable for both phase contrast and electron microscopy. Other ears exposed at 95 dB SPL were allowed to recover 7, 28, or 70 days before fixation. The number of cisternae in the peripheral membrane system of many outer hair cells was increased from three to six to as many as 30. Similar membranes appeared as whorls within the cells. The proportion of altered cells was greatest in upper second and lower third turns and increased with exposure levels. Recovery toward normal membrane configuration was evident at seven days and only minor variations remained after 28 and 70 days.
Physiological Aspects of Certain Laryngeal Features in Stop Production
Authors: Hirose Hajime , Lisker Leigh , Abramson Arthur S.
Published: October 2005

Multichannel EMG recordings were made of the instrinsic and extrinsic laryngeal muscles during production of intervocalic labial stops of five phonetic types: explosive voiced inaspirate, implosive voiced inaspirate, voiced aspirate, voiceless inaspirate. and voiceless aspirate. The recorded data, computer processed to obtained average EMG values, indicate that abductor and adductor muscle groups follow coordinated patterns of activity corresponding to opening and closing of the glottis. In particular, the interarytenoid and posterior cricoarytenoid muscles showed reciprocal patterns both in degree and timing of activity. In addition, the sternohyoid showed marked activity for the implosive stop, presumably correlated with an abrupt lowering of the larynx. In a second experiment using the same speaker and the same syllables, motion pictures of the glottis were taken by means of a flexible fiberscope. The overall conclusion suggested is that active adjustments of the glottis in terms of coordinated muscle activity, and the timing of this activity relative to supraglottal events, are the decisive factors by which the various stop consonant types are differentiated. [This research was supported by the National Institute of Dental Research through an NIH grant]
Activity of Some Extrinsic and Intrinsic Tongue Muscles in the Articulation of American English Vowels
Authors: Harris Katherine S. , Raphael Lawrence J.
Published: October 2005

Most previous electromyographic studies of tongue muscles have been limited to those extrinsic muscles which are easily accessible: the genioglossus and palatoglossus. Recent experiments have provided access to the styloglossus, among the extrinsic muscles, and to the intrinsic fibers of the tongue. Thus, a fuller picture of muscular synergisms in the positioning and shaping of the tongue is beginning to appear. This study reports findings from three subjects who spoke 10 American English vowels in a labial consonant frame preceded by schwa. All electromyographic activity was recorded from hooked-wire electrodes inserted into the various muscles by means of hypodermic needles. The results reveal as many differences as similarities between the articulatory strategies of the subjects. It appears that the similar articulatory configurations that underlie the linguistically relevant acoustic structures of the vowels can be achieved by a variety of muscular patterning. [This research was supported by the National Institute of Dental Research.]
Tongue and Lip Activity During Australian Aboriginal (Walbiri) Articulation
Authors: Proffit W. R. , McGlone R. E. , Barrett M. J.
Published: October 2005

Recording equipment was transported to Yuendumu, N. T., Australia, to obtain data on tongue and lip activity of aboriginals during speech and swallowing. Strain gauge pressure transducers were fitted into custom constructed plates to be placed in the speaker's mouth to record tongue and lip contact at several locations. Eighteen speakers whose native language is Walbiri acted as subjects. Eight prerecorded Walbiri words and four nonsense words, five repetitions each, were presented to the subjects. These tokens contained three of the Walbiri modifications of the phoneme /t/ situated intervocalically in each word. Distinct articulation patterns of both tongue and lips were found for the three phonemes regardless of whether they were located in meaningful or nonsense words. Furthermore, pressure patterns for the phoneme most like the American language /t/ were very similar to patterns for American speakers. This was true even though tongue and lip movements during swallowing were quite different from Americans. [Kenneth Hale assisted in preparing the speech stimulus. Support from the Fulbright program, NIDR, and Southern Society of Orthodontists is gratefully acknowledged.]
A Two-Dimensional Strain Gauge Transducer System for the Lips and Jaw
Authors: Abbs J. H. , Gilbert B. N.
Published: October 2005

A strain gauge transduction system was designed and constructed for simultaneous observation of the movements of the upper lip, lower lip, and jaw in both inferior-superior and anterior-posterior dimensions. Empirical verification of the system's structural loading factor, frequency response, linearity, and phase response suggests that it provides a favorable alternative to earlier lip and jaw monitoring devices. Some examples of the two-dimensional multistructure movement patterns obtained with this device will be provided and discussed. [Research supported in part by NIDR/grant.]
Palatoglossus Function in Normal Speech Production—Electromyographic Implications
Authors: Lubker James , Salinard Judith Berezin , May Kenneth
Published: October 2005

Fine-wire-inserted electrodes were placed in the right and left palatoglossus muscles of 14 subjects. Two to four simultaneous placements were accomplished for each subject. Electromyographic signals were recorded while each subject produced a speech sample designed to consider palatal and lingual movements. The data strongly suggest that, while palatoglossus function for the nonspeech act of swallowing is highly consistent within and between speakers, its specific function in speech production is less consistent. !n some subjects, the palatoglossus appears to function to actively lower the palate for nasals and at the end of utterances, while for other subjects it does not. In some subjects activity appeared related either to tongue movements or to stretch reflex. Finally, within any one subject, function was often variable. The data are discussed primarily with regard to palatoglossus function, although other aspects, i.e., its variability, which will be discussed in detail in subsequent papers, are also mentioned. [Research supported by NIDR, PHS grants.]
Piezoelectric Arrays
Authors: Mueller R. K.
Published: October 2005

The first practical piezoelectric array was demonstrated by Langevin early this century. It was a composite quartz transmit/receive unit for underwater search and surveillance. A wealth of new piezoelectric materials have since been developed. Sophisticated array processing techniques evolved and became practical with increasing speed and capacity of digital computers. These developments led to the present wide range of piezoelectric arrays with widely differing design objectives. A general survey of the state of the art will be given, and, as a specific example, some design features of a 96 × 96 holographic receive array presently under construction will be discussed.
Condenser-Transducer Arrays for Recording Acoustic Holographic Data in Real Time
Authors: Nigam A. K.
Published: October 2005

Two-dimensional transducer arrays consisting of a mosaic of condenser-microphone elements appear to be ideal acoustic analogs of the photographic plate for recording holographic data in real time. Such transducer arrays, employing either external or electret biasing, are reviewed in the present paper. In particular, two relatively simple and inexpensive designs [see for example A. K. Nigam, K. J. Taylor, and G. M. Sessler, Acoustical Holography, Volume 4, G. Wade, Ed. (Plenum, New York, 1972), pp. 173–194] are described in detail. Simplicity of design is achieved by using a single solid-dielectric diaphragm, which is shared by a large number of microphone elements of the array, and by employing sequential data sampling, which eliminates expensive repetition of similar signal-processing equipment for each element of the array. Electrical and acoustical characteristics, such as interelement cross talk, element sensitivity, frequency range of operation, and the real-time capability for the two array designs are reported. These are found to compare favorably with the characteristics for the more conventional piezoelectric arrays. Acoustic images made with 16 × 6 element prototype arrays of the present design are also discussed.
Statistical Parameters under Stationary Random Excitation
Authors: Piersol A. G.
Published: October 2005

Fundamental statistical parameters used to describe stationary random vibrations are viewed with emphasis on those parameters of special concern in structural response and failure prediction problems. Included in the review are correlation and spectral density functions, instantaneous and peak value probability density functions, arbitrary level crossing statistics, and elementary considerations in the first passage problem. The relevance of the various statistical parameters to the prediction of structural fatigue and extreme value failures, assuming simple failure mechanism models, is introduced in qualitative terms. Both theoretical and experimental results are displayed to illustrate important relationships. Special attention is given to the importance of underlying assumptions inherent in classical applications, in particular, the excitation normality and system underlying assumptions. Data are presented to demonstrate the impact of common nonlinearities on such response parameters as the instantaneous and peak value probability density functions. Finally, the importance of the stationarity and associated constant parameter system assumptions are discussed from a practical viewpoint. Illustrations are included to clarify the types of errors that result when nonstationary random excitations and responses are analyzed as if they were stationary.
Fatigue and Crack Propagation Analyses under Stationary Random Excitation
Authors: Leybold H. A.
Published: October 2005

An accurate analytical method for predicting the fatigue life of an aircraft structure under actual operating conditions is not a reality today. Four major parameters (i.e., material behavior, environment, structural configuration, and operational loads) plus the three phases of the fatigue process (i.e., initiation, crack propagation, and fracture) are involved in the prediction process and attest to the complexity of the problem. In addition, each parameter has its own statistical variability, which further complicates the problem. Even when treating each of the variables as independent events, the prediction process is still a complex one. This paper will deal with only one of the variables involved in the overall prediction process, namely, operational or random loads. Many investigators have proposed techniques for predicting life under random loading—with varying degrees of success—based on experiments, empirical rules, and/or past experience. The most noteworthy of those techniques are reviewed, and their capabilities and limitations assessed. The prediction of crack growth in aircraft structures is also of interest from a safety and reliability standpoint, as well as for setting up inspection and maintenance schedules. Current crack-growth prediction techniques, which incorporate fracture mechanics methods, are reviewed and assessed. A bibliography of pertinent references is included.
First Passage Analyses under Stationary Random Excitation
Authors: Yao J. T. P.
Published: October 2005

A structure fails whenever its response to excitation reaches one or more limiting values. Structural responses include deformations and internal forces, of which the limiting values are based upon various failure criteria for the material. The failure probability of a structure subjected to random excitation can be found as the first passage probability of the response process across the most severe limiting strength values or deformation barriers. This problem can be solved in principle when the structural response is represented by a Markov process. However, exact solutions are available only for some first-order Markov process. Consequently, approximate methods have been suggested by various investigators. In this presentation, an attempt will be made to summarize and review the Poisson approximation with several independence assumptions, two-state Markov process assumption, clump-size estimation, use of an equivalent first-order Markov process or a renewal process, simulation and numerical diffusion, upper and lower bounds, nonapproaching excursions, and the principle of maximum entropy of the total number of excursions.
A Study of Very Low-Frequency Attenuation in the Deep Ocean Sound Channel
Authors: DiNapoli F. R. , Powers M. R. , Browning D. G.
Published: October 2005

The fast field program (FFP) is used to study sound propagationin a deep ocean sound channel for the frequency range 1–200Hz. Typical sound velocity profiles from the Atlantic and Pacific Oceans are used. Both the velocity profile and bottom depth are assumed to be invariant with range. The channel cutoff frequency is determined and the bottom loss contributionto the measured values of attenuation is estimated. Comparison is made with recent experiments.
Probability Density Function of the Time Average of Sound Pressure Level Measurements in a Reverberant Room Excited by Random Noise
Authors: Ingalls Douglas J.
Published: October 2005

The probability density function of the time average of the sound pressure levels (measured in decibels) of a reverberant room excited by a finite bandwidth of random noise is (approximately) Gaussian for a stationary source and stationary receiver. The mean of the distribution for a finite integration time is less than the mean for an infinite integration time. The difference (in decibels) is given by 4.8/BT, where B is the bandwidth in hertz and T the integration time in seconds. The normalized variance of the distribution is given by 19/BT. The results imply that narrow-band measurements in a reverberant room need to be carefully defined if errors in the measurement due to finite integration times are to be minimized.
New Reverberant Room Acoustic Test Facility
Authors: Holmer Curtis I. , Andersen Douglas W.
Published: October 2005

A test facility recently constructed at BBN consisting of a pair of reverberant rooms for transmission loss (TL) measurements and sound power level measurements is described. Because of space limitations, existing facilities, and the need to measure models to high frequencies, the rooms were limited to 3100 ft3 a volume. The principle instrumentation used for measurements includes an electrically scanned multiple microphone array and a real-time analyzer. A unique feature of the facility for TL measurements is a modular demountable steelfiller wall which permits easy alteration to accommodate samples from 3 ft × 3 ft to 9 ft × 14 ft in size. A major concern during the evaluation of the facility was the intention to make sound power level measurements in accordance with ANSI S1.21. It was found that by using an eight microphone array and a rotating diffuser the rooms easily meet the requirements for measuring broad-band noise. For measuring tones, however, a low-frequency absorber and two suitably chosen source positions were also required in order to meet the performance requirements of the standard. Criteria for the selection of source positions and rotating diffuser operating conditions are discussed.
Transportation Noise—Airplane Noise Reduction
Authors: Hubbard Harvey H.
Published: October 2005

Current Federal noise regulations will be discussed along with their impact on community noise exposure. Brief references will be made to specific technical areas where significant advances in noise reduction have been made and to noise reduction goals for the future.
Community Noise—Surface Transportation
Authors: Thiessen G. J.
Published: October 2005

Noise due to surface transportation is still rising, but there is evidence that it is leveling off. The important change in the last five years has been the increase in knowledge of the relative importance of the noises from exhaust, intake, engine radiation, tires, and airflow and the extent to which they can be modified at reasonable cost. Trucks and motorcycles are still the most intrusive noise sources, with the latter showing some signs of improvement with the introduction of a water-cooled model by Suzuki. Radically new engines, such as the Wankel and gas turbine engines, are still too close to the experimental stage to show what they can do to decrease noise and abide by emission standards. Legislative control is the primary mechanism for overcoming the competition problems, which make manufacturers reluctant to incur the cost of noise reduction in the worst noise sources. More inclination to experiment has been shown by public bodies in road layout, design, and construction of barriers, but not always with full knowledge of the pitfalls and limitations of this approach.
Noise Intrusion from Police Helicopters over Los Angeles Communities
Authors: Meecham W. C. , Lane S. R.
Published: October 2005

Measurements of police helicopter noise were made during surveillance flights over communities in several cities in the Los Angeles area. Small light observation-type helicopters (Hughes 269 and 300 and Bell 206) are used for emergency and surveillance work by the police departments of most cities in the Los Angeles area, and by the sheriff's departments in the southern California seven county area. These helicopters typically fly over the various communities several times each day and during the late evening hours. Operation of these helicopters at 500- to 1000-ft altitudes results in noise levels of 70–80 dBA in the residential communities. Helicopter flights over schools and colleges caused noise levels of 65–75 dBA inside the classrooms. This is 10–20 dB above the maximum allowable limit of 55 dBA for acceptable speech communication in offices and classrooms. In the Santa Monica area, late night flights and search patterns caused noise levels of 100–115 EPNdB over hospitals and convalescent homes. These levels are in violation of municipal noise codes and exceed the federal landing noise limits for new jet aircraft.
The Effect of Sample Size on Freeway Noise Measurements
Authors: O'Neall J. Stephen , Wallace C. E.
Published: October 2005

Traffic noise levels were recorded along two freeways having significantly different traffic densities. These recordings were analyzed to yield the A-weighted noise levels L50%, L10%, and L1% for a range of sample sizes. Standard deviations of these noise levels were computed and plotted against both the duration of the sample and the number of vehicles passing within the sample. The results show that the standard deviations of the measurements vary with traffic density when plotted versus sample duration but do not depend on traffic density when plotted against the number of vehicles in the sample. For the measurement of L50%, L10%, and L1%, a 1-dBA standard deviation requires 100, 160, and 300 vehicles, respectively. Similarly a 3-dBA standard deviation requires 19, 25, and 90 vehicles, respectively.
A Study of Harshness in Low-Pitched Musical Tones
Authors: Kohut J. , Mathews M. V. , Miller J. E.
Published: October 2005

Low-pitched tones with many harmonics as typically generated by musical synthesizers often sound rough or harsh. A theory of the quality of musical tones is proposed which relates harshness to the spacing of harmonics relative to the critical bandwidths of the ear. If the harmonics are sufficiently closely spaced so that more than one strong harmonic falls within a critical band, the tone quality will be characterized as harsh. The lower the frequency of a tone, the closer the spacing of its harmonics and, hence, the greater its tendency to be harsh. Such a tone can be smoothed by attenuating selected harmonics so as to leave only one prominent harmonic in each critical band. Tones with controlled harmonic amplitudes were synthesized by both digital and analog devices and evaluated with listening tests. The frequency range from 500 to 1500 Hz seems most critical in the generation of harshness. Attenuation of selected harmonics by 12 dB is optimum for smoothing tones. Greater attenuation produces a too hollow sounding timbre.
Consulting Experience with the New Federal Highway Noise Standards
Authors: Copley Lawrence G.
Published: October 2005

In April 1972, the Federal Highway Administration issued its interim noise standards [Policy and Procedure Memorandum 90-2: Interim Noise Standards and Procedures for Implementing Section 109(i) of Title 23 U.S.C.]. These standards will apply on an interim basis to all Federal Aid highway projects submitted for location approval after 1 July 1972. This paper addresses procedural aspects of the Standards rather than policy questions. The paper draws on experience in performing noise evaluation studies in accordance with the Standards for several typical highways projects. Three key features of the Standards are discussed. First, L10 as a measure of community noise level at different times of the day is reviewed in comparison with L50, which is easier to forecast accurately and less expensive to measure in the field. Second, the use of maximum traffic volume noise levels is reviewed, given that highway noise may be more annoying in off-peak hours such as evening or nighttime, when traffic volumes are less and the highway noise generally has a much different character. Finally, the highway noise forecast procedures prescribed in the Standards are discussed.
A Comparison of the Predicted and Actual “Noise Pollution Level” for Vehicular Traffic on Limited Access Highways
Authors: Oslac M. J.
Published: October 2005

A superhighway near a suburban community formerly connoted convenience and instant accessibility to job, recreation, shopping, etc. Today, land values are more often relating to environmental serenity. This awareness of highway noise has prompted Environmental Impact Studies prior to the final design of new highways. The surrounding environment must be protected at least to the extent of the recently adopted FHWA Policy and Procedure Memorandum 90-2, which for a 24-hour period sets the noise limits which may not be exceeded more than 10% of the time. While this may be a good starting point, the Policy lacks the requirement that a measure of the background be made. Robinson's Noise Pollntion Level (NPL) provides a more realistic value of annoyance from vehicular traffic in that it provides for inclusion of the background. It thus offers a possibly better guideline. The recent study described in this paper utilized the L10 and L90 values calculated from the NCHRP Report No. 117 to predict the NPL for four eastern United States communities adjacent to limited access highways. Measurements were made at the four sites and an exact NPL was calculated using the energy mean value and the standard deviation. An attempt was then made to correlate these values with community response questionnaires. These values were also compared to the L10 levels in PPM 90-2. The implications of using NPL in Environmental Impact Studies is discussed.
Noise Generation Mechanisms for Passenger Car Tires
Authors: Siddon T. E.
Published: October 2005

Starting with the premise that intense aerodynamic mechnisms are responsible for a significant fraction of the noise radiated by a “relatively smooth” tire rollling on a “relatively smooth” surface, experiments have been conducted to identify and quantify such mechanisms. The experiments, conducted on a passenger car vehicle equipped with rib-type tires, include flow visualization studies and fluctuating pressure measurements both in the vicinity of the tire-road interface and in the acoustic far field (i.e., with the microphone mounted at the end of a 5-ft boom). A unique technique, involving cross correlation between the near-field pressure and the far-field sound measured by the boom mounted microphone, yielded significant information on the distribution of acoustic sources in the vicinity of the tire. These measurements indicate that a strong unsteady flow field does indeed exist in the region immediately behind the tire-road interface, and that this unsteadiness makes a dominant contribution to the noise. Alternative models for the aerodynamic mechanism, based on Hayden's “air-pumping” hypothesis, and a newly advanced “vortex interaction” process, are described and compared.
A Low Cost Approach to Area-Wide Community Noise Monitoring
Authors: Siddon T. E. , Harford K. D.
Published: October 2005

A new approach to noise survey work emphasizes the importance of spatial and temporal noise level variations with less stress on frequency content. It is shown that a low cost sound monitoring package, A-weighted at the input stage, and with a dynamic range of 45 dB, yields adequate information on which to base a concise, statistical model of the acoustic landscape. Because of the low cost of individual terminal units, a large number of units may be operated over an extended land use area. This ensures that important spatial information is not lost. Such a detailed picture is not possible with the more conventional sequential (point to point) techniques that are normally employed. The format for a typical area-wide noise level survey is presented, and the usefulness of the data obtained to urban planners and legislators is briefly described.
In-Service Tire Vibration Investigation
Authors: Reiter William F. , Harper Leon J. , Eberhardt Allen C.
Published: October 2005

An experimental research program has been initiated to measure and correlate the sound and vibration spectra of in-service truck tires. The objective of this work is to obtain a detailed bank of tire sound and vibration data that will aid in a better understanding of tire noise generating mechanisms and how they are influenced by important parameters such as load, tread type, tread wear, and speed. This work extends the recent work completed by the National Bureau of Standards entitled “Peak A-weighted Sound Levels Due to Truck Noise.” Initial results of the telemetered vibration data for typical truck tires will be presented. [The Office of Noise Abatement, U. S. Department of Transportation, is acknowledged for support of this project.]
Twenty Years of Medical Ultrasonic Imaging
Authors: Reid John M.
Published: October 2005

Ultrasonic imaging systems are becoming important in medicine. Our growing understanding of fundamental acoustical-tissue interactions may contribute important new abilities. Absorption and velocity of the sound vary with the structure of tissue and together determine the resolution and penetration of any diagnostic system. The reflecting and scattering properties of tissues are little known although much can inferred from clinical studies. Quantitative work in scattering is only beginning. Imaging systems can be classified on the basis of their range-versus-depth resolution and scanning time-versus-complexity tradeoffs. Early pulse-echo scanners had such “new” features as real-time imaging and gray scale response. Many medical centers now use contact and waterbath scanners. Newer pulse-echo and CW systems require complex electronics that were not feasible before integrated circuits were available. A promising new area is use of special target properties to identify reflecting objects. For example, working systems identify the Doppler-shifted backscatter from moving blood to map areas of flow. Present systems are adaptable to such imaging techniques.
High Resolution Ultrasonic Scanning System
Authors: Hurwitz M. J.
Published: October 2005

We have built and tested several focused-arc ultrasonic transducers for use in nondestructive characterization of flaws in thick metal sections. These transducers transmit and receive ultrasonic pulses at frequencies 2.25 or 4 MHz and produce diffraction limited beams at all ranges including the classical nearfield region since the beams are essentially in focus at all ranges. We have used both contact and immersion transducers in conjunction with a mechanical scanner and display package and have produced B-scan images of holes and flaws from 1- to 20-in. depths into metal specimens. Images of patterns of drilled holes have been made demonstrating the resolving of 132- in.-diam holes about 116 in. apart through 212 in. of aluminum. Several other ultrasonic images and comparisons of these with other NDT techniques will be shown. [This work has been supported by the U. S. Navy under contract.]
Speech Producing Abilities of Primates and Human Evolution
Authors: Klatt Dennis H. , Lieberman Philip , Crelin Edmund S.
Published: October 2005

Comparative anatomic and acoustic studies of the supralaryngeal vocal tracts of living and extinct primates indicate that speech production has been an important factor in human evolution. The sounds of human speech make human language a rapid medium of communication through a process of speech “encoding.” The presence of the human vowels /a/, /i/, and /u/ facilitates this process. The supralaryngeal vocal tracts of newborn Homo sapiens and the living nonhuman primates are similar and resemble the reconstructed vocal tracts of fossil Australopithecine and Neanderthaloid hominids. Vocal tract area functions that were directed towards making the best possible approximations to the human vowels /a/, /i/, and /u/, as well as certain consonantal configurations, were modeled by means of a computer program. The lack of these vowels in the phonetic repertoires of these creatures, who lack a pharyngeal region like that of adult Homo sapiens, may be concomitant with the absence of speech encoding and a consequent linguistic ability inferior to modern man.