Showing papers in "Canadian Acoustics in 1992"

On neutral-tone syllables in Mandarin Chinese

Abstract: One of the characteristic and hard to be grasped features in Mandarin Chinese is the so-called neutral-tone (hereafter NT) syllables, which is neutralized from corresponding normal stressed syllables. Perceptually, The NT syllable sounds quite weak, and must be attached to other syllable as a dependent morpheme in polysyllabic words. However, it does not equal to the unstressed syllables in common, in stead, it forms an important morphophonemic contrast to the normal type one in bisyllabic words. Consequently, it might be of benefit to Chinese speech processing to clarify the phonetic nature of the NT syllables. Many relevant approaches from different viewpoint have been contributed before, this study is concerned in their phonetic characteristics. The discussion is based on a relevant acoustic measurements and analysis referred to a corpus of materials including over 200 of NT syllables, all of them are occurred as second morpheme in different category of neutral type bisyllabic words. The hypothesis is that the perceptual feature of the NT syllables may be caused by a combination of multiple acoustic effects, in stead of any single factor. Therefore, this kind of syllables must own their special acoustic patterns

Can an inactivated hearing aid act as a hearing protector

Abstract: The authors assess the effectiveness of various models of inactivated hearing aids as hearing protectors. Insertion loss was measured in a free field using an acoustic head simulator specifically designed for hearing protector evaluation

A stationary approximation in matched-field processing for a moving underwater acoustic source

Abstract: A normal-mode model for the acoustic field due to a moving source was recently used in the development of procedures for applying matched-field processing (MFP) techniques to a moving source This approach involved matching `measured' array covariance matrices at multiple frequencies using replica matrices computed with a phase-expanded form of the Hawker model (1979) Excellent results were obtained, but the technique was compute-intensive A procedure is described for using snapshot vectors at a single frequency to generate the replica matrices By comparing the performance of the MFP techniques applied to simulated data, it is shown that this new stationary approximation procedure allows the position of a moving source to be estimated as accurately as, but much more efficiently than, the full multiple-frequency procedure

Shallow water acoustics: a review of DREA research

Abstract: From 1949 to 1989, the Defence Research Establishment Atlantic (DREA) conducted research in shallow water environmental acoustics in support of passive sonar applications in submarine detection. The emphasis was on collecting ambient noise and transmission loss data in a variety of geographical areas of interest with different seabed types in all seasons of the year. Significant progress was made in understanding the physical mechanisms governing the acoustic environment, especially the role of the seabed. The modelling capability improved substantially, drawing on computer codes developed inhouse and elsewhere. An important lesson learned was that passive detection is governed by the sum of transmission loss and ambient noise level, which varies from site to site much less than each component considered separately. Despite the progress made, much remains to be done, particularly with regard to the performance of hydrophone arrays in shallow water environments. The way ahead should include: experimental studies of array performance; environmental acoustics measurements relevant to active sonar in shallow water; bottom-mounted sensors (including geophones); and integration of oceanographic and geophysical databases with sonar models in three-dimensional environments

Modelling azimuthal and vertical directionality of active sonar systems for undersea reverberation

Abstract: Traditional methods for modelling undersea reverberation where either the transmitter or receiver has azimuthal directionality approximate the azimuthal component by sector coverage. Often, the effects from other than a main lobe are ignored. In some cases, the width of the sector is chosen such that the azimuthally-integrated response is the same for the sectored coverage as the original sonar in the horizontal plane. Unfortunately, should the sonar have both azimuthal and vertical directivity (which is often the case), accounting for only the main lobe or using a simple azimuthal integration may lead to erroneous reverberation estimates. Historically, inclusion of the full directionality or beam pattern has been too computationally costly to consider, but with the proliferation of modern high-speed computers, this is no longer the case. The full directionality can and in many cases should be included

`DETECTSOUND' and `dBOHS': a software package for the analysis of health and safety in noisy workplaces

Abstract: Every year serious injuries occur in noisy workplaces because a warning signal is not heard. Very few practical tools allowing direct prediction of the ability to detect acoustic signals in noisy environments are available. The Groupe d'Acoustique de l'Universite de Montreal (GAUM) has developed a computerized model called DETECTSOUND which runs on an IBM-PC compatible and which can predict the capability of workers to detect auditory warning signals in noise. To run DETECTSOUND, it is necessary to obtain 1/3 octave band levels at each work station. dBOHS was designed to obtain this information from a recording made on the site using a digital audio-tape recorder and a hand-held controller

Acoustic measurements of vocalic nasality in Mandarin Chinese

Abstract: The assimilation of nasality onto vowels spoken in the context of nasal consonants has been documented by research using various methods (aeromechanical, acoustical, biomechanical, perceptual). The research reported used acoustical analog recording and digital analysis techniques to quantify assimilation nasality patterns in Mandarin Chinese as a function of vowel height, place of articulation of the following nasal consonant, and tonal characteristics of the vowel

Application of modern room acoustical techniques to the design of two auditoria

Abstract: Recent advances in the study of room acoustics are formidable. The modern understanding of the behaviour of sound in rooms now allows for much more freedom and confidence in design. The design of two new rooms will be presented. The first is a 3500 seat Assembly Hall of Jehovah's Witnesses to be used primarily for speech. It features a terraced floor plan to provide early reflected sound throughout the audience. The second room is a 300 seat recital hall at Conrad Grebel College in Waterloo, Ontario. In this room, special attention has been given to platform acoustics using the recent findings of Grade (1989) and Naylor (1988). Both designs demonstrate the practical application of modern acoustical research

Hand-arm vibration associated with the use of riveting hammers in the aerospace industry and efficiency of `antivibration' devices

Abstract: Riveting hammers are widely used in the aerospace industry for assembling aircraft panels. The process of riveting usually involves punching strokes on the rivet head while a bucking bar is held on the other end of the rivet for closing it up. The installation of a rivet takes only a fraction of a second but is known to subject both the operators of the riveting hammer and of the bucking bar to significantly high levels of vibration. Such vibrations are susceptible to contribute to the development of vibration white finger disease of which Raynaud's phenomenon is most widely known. The authors evaluate the exposure levels associated with the use of typical riveting hammers and bucking bars used in an assembly plant some of these devices being characterized as `antivibration' devices, in an effort to evaluate their efficiency for reducing vibration exposure following the ISO 5349 guidelines. In addition, an evaluation of specially designed vacuum pads, mainly aimed at reducing the noise radiated, to establish their potential effect on hand-transmitted vibration levels

Preliminary simplified models for predicting sound propagation curves in factories

Abstract: Predictions of factory noise levels are based on predictions of the factory sound propagation curve-the variation with distance from an omnidirectional point source of the sound pressure level minus the source sound power level; SP(r)=L p (r)-L w . While more accurate approaches such as ray tracing exist, from a practical point of view there is considerable scope for developing simplified empirical prediction methods. In fact, several such models exist. However, these have short-comings which warrant the development of a new model. The approach taken was to predict the slope(s) and absolute level(s) of the sound propagation curve, approximated by one or more straight-line segments. With this in mind, octave-band sound propagation measurements were made in a number of empty and fitted factories. The curves were approximated by one or two straight-line segments. The intercepts and slopes of the segments were then determined. The development of preliminary simplified prediction models from the results is discussed

Sound masking systems: a guideline

Abstract: Sound masking is suitable for both open and closed offices to improve acoustic privacy. Space planning with sound masking can avoid the need to build partition walls above the ceiling to achieve confidential privacy between closed offices (when the door is closed). The judicious use of sound masking around closed offices and meeting rooms can increase acoustic security by reducing the signal to noise ratio ratio in the surrounding areas

Sound power determination using the sound intensity scanning technique

Abstract: Sound intensity is the primary quantity required to compute the sound power of sources, which is given by the surface integral of the product of the normal component of the sound intensity and the associated elemental area over any surface fully enclosing the source. In the scanning method, the probe is moved continuously along one or more prescribed paths on the surface. The surface average value of the normal component of sound intensity is obtained in a few scans, instead of independent measurements at several points. This method is relatively quick and easy to perform and gives good results for measurements requiring engineering grades of accuracies. The author examines the range and effect of some of the major parameters associated with the scanning technique, for providing guidance to the user and to the standardization of the procedure

Application of FIR digital filters to model human auditory perception of short-time amplitude in low-frequency rapid spectrum change

Abstract: FIR (finite impulse response) filters are applied using CSL, in the quantization of the SPL amplitude component of linguistic resonant pharyngeal consonants in word-initial CV environments. Only the onset consonant amplitude responses are modelled, with FIR transfer functions corresponding of SPL acoustic responses: glottal excitation (forced response), separate from the pharyngeal transmission (natural response). The FIR transfer function (impulse response) system design has the following properties: pharyngeal transmission interpreted as odd amplitude/even phase; this is differentiated from glottal source characteristics: even amplitude/odd phase. This motivates a DTLTI system

Trains, planes, & fishing boats: a geophone sensor for underwater acoustics

Abstract: Usually, ocean acousticians use hydrophones (i.e. pressure sensors) for very-low-frequency measurements, either placed on the seabed or suspended in the water. Occasionally, they use transducers that sense the particle velocity associated with the acoustic wave in the water. Some investigators have been using geophones (i.e., velocity sensors) coupled to the seabed itself. Geophones measure the motion at the seabed, which can be different from that in the adjacent water mass. In particular, geophones-unlike hydrophones-can sense the propagation of shear waves in the seabed. Seismologists have been using geophones in their Ocean Bottom Seismometer (OBS) packages for years. The author describes the configuration, testing, and calibration of an OBS for underwater acoustic experiments

Digital generation of the high quality audio signals with the NeXT computer

Abstract: A computer-based digital function generator can generate any arbitrary type of signal in the frequency range from 0 Hz to 20000 Hz, S/N=95 dB, and with no harmonic or intermodulation distortion (when based on 16-bit, 44.1 kHz-sampling rate D/A converter). Frequency stability is determined by a quartz clock in the D/A converter which has an accuracy in the order of 1/10 7 . Generation of sinusoidal waves is of primary importance in digital synthesis since due to the Fourier theorem any periodic wave may be constructed via additive synthesis (an addition of pure tones with appropriate amplitudes and phases). There are many alternative methods to digitally generate pure tones. Very often real-time synthesis is accomplished by using a sine function look-up table. A limitation to this approach is the short length of the sine table. In order to synthesize any arbitrary frequency using the look-up table method, one has to synthesize the values of the sine function using an interpolation process. Interpolation between sine samples leads to the generation of harmonic and intermodulation distortion by this algorithm. Another problem is that synthesis of more complex signal (combinations of several sinusoids with certain amplitudes and phases) in real time could put too much performance demand on the computer's DSP chip or microprocessor

The effect of aging on reaction time in auditory detection and discrimination tasks

Abstract: This research investigated the effect of aging on sensory information processing and decision-making. Detection thresholds in quiet and in noise and temporal acuity, and their associated choice reaction times were measured in two groups of normal-hearing subjects, differing in age. All three psychophysical tasks utilized a four-interval forced-choice procedure. The results indicated that there were no differences in duration discrimination or choice reaction time as a function of aging. However, the variability in choice reaction times was significantly greater for the older group, signifying greater heterogeneity in the time for decision-making. Erroneous responses generally took longer to make than correct responses. For the younger group, the erroneous response time increased with task complexity

Performance of combustor with acoustic augmentation of primary zone air-jet mixing

Abstract: Earlier work established that the dilution-air mixing processes of a small tubular combustor of normal design could be beneficially controlled by acoustic means; specifically a desired exit plane temperature distribution may be achieved. From these results it was inferred that the entrainment rate and mixing of the dilution-air jets was increased by the acoustic pulsation. These encouraging results promoted detailed investigations into acoustically pulsed free-jet mixing, and showed that the entrainment and entrainment coefficient of the jet could be considerably increased, by up to six times. Also, work on acoustically pulsed jet mixing with a confined crossflow, showed that mixing was significantly increased and penetration at least 100% increased. The success of these activities has now resulted in the technique being applied to the air jets of the combustor primary zone, because of the potential for control and improvement in combustor performance

Modelling auditory scene analysis: a representational approach

Abstract: Speech is normally heard in the presence of other interfering sounds, a fact which has plagued speech technology research. A technique for segregating speech from an arbitrary noise source is described. The approach is based on a model of human auditory processing. The auditory system has an extraordinary ability to group together acoustic components that belong to the same sound source, a phenomenon named auditory scene analysis by Bregman (1989). Models of auditory scene analysis could provide a robust front-end for speech recognition in noisy environments, and may also have applications in automatic music transcription. Additionally, the authors hope that models of this type will contribute to the understanding of hearing and hearing impairment

It's a small world: underwater sound transmission from the southern Indian Ocean to the western North Atlantic

Abstract: Sounds transmitted through the air are rarely detectable more than a few kilometers from their source. Beneath the sea, however, acoustic signals at frequencies less than a few hundred Hertz can often be detected at ranges of several thousand kilometers. The authors show that low-frequency acoustic signals entering the ocean near Heard Island in the southern Indian Ocean can be detected off the east coast of North America and that relatively crude modelling is sufficient to reproduce the signal levels observed, despite the long path length of approximately 17000 km (17 Mm)

Separation of acoustic multipaths in Saanich Inlet

Abstract: Acoustical scintillation measurements can provide a basis for determining the properties of ocean structure in coastal waters and can be used as a tool to remotely measure oceanographic processes (e.g. current and turbulent structure) which differ markedly from processes in the open ocean. A scintillation experiment in 1989 was carried out in a coastal environment in British Columbia, Canada in order to relate acoustic characteristics to the oceanography. The experimental site was Saanich Inlet which is a deep (220 m), quiescent (maximum currents 10 cm.s -1 ) and stratified fjord. The goal is to compare acoustic propagation through this relatively undisturbed, coastal environment with previous measurements in a turbulent tidal channel

On the Modelling and the Prediction of the Vibroacoustic Behaviour of an Aircraft Structure

Abstract: This paper summarizes the first step of a long-term research program focusing on the modeling and prediction of the vibrational and acoustical behavior of an aircraft structure. The final goal pursued is to provide the aeronautical industry with guidance for cabin sound-proofing with the help of a versatile, physical and easy-to-use model. Two main subjects tackled in this paper are: ® The free vibrational behavior of the aircraft structure. © Effects of the rear pressure bulkhead on the cabin noise.

Insertion loss of multi-chamber mufflers

Abstract: Expansion chamber mufflers are commonly used as noise control devices in piping systems, when the application of passive silencers is not possible. Single expansion chamber mufflers has been studied extensively. Lamancusa (1988) conducted a parametric study on the transmission loss of double expansion mufflers. However, insertion loss is more meaningful than transmission loss for the effect of the inlet and tail pipe lengths are properly taken into account. A parametric study on the insertion loss of two chamber and three chamber mufflers was conducted and preliminary results of our study are presented. The results assume anechoic termination at the tail pipe exit and hence the tail pipe effects are neglected. Further, the damping due to the flow medium and the pipe walls is negligible

Discrimination of frequency transitions as a function of varying spectral cues among young and elderly adults

Abstract: Next to the changes that are noted in hearing sensitivity loss, the deterioration in speech discrimination is the most commonly recognized characteristic of age-related changes in auditory function. This well-documented reduction in speech discrimination is a pivotal auditory problem associated with aging given that elderly individuals without a high sensitivity loss report difficulty in understanding speech in optimum conditions; that is speech perception difficulties are greater than would be expected on the basis of pure tone sensitivity levels. One relevant aspect underlying the difficulties that elderly adults experience may be a function of the brevity and rapid spectral changes which characterize some speech segments. Indeed, reduced spectral and temporal resolution has been reported for elderly listeners who demonstrate normal pure tone thresholds (Cranford and Stream, 1991; Maden and Feth, 1992; Robin and Royer, 1989; Trainor and Trehub, 1989). The authors investigated how various spectral characteristics influence discrimination of short duration, dynamic signals as a function of age

Etude de L'efficacite d'un Belier Amortisseur

Abstract: The aim of this work was to check the efficteveness of a steel bucking-bar with two half-filled mercury pits in reducing the sound pressure level of a riveting gun. For that purpose, a sound pressure level comparison for the two kinds of bucking-bar, standard and with mercury, was realized. The effects of some parameters, like the bucking-bar applied force or the impedance of its support were investigated. The behaviour is similar to that of a band-stop filter.

Reciprocal travel time scintillation analysis

Abstract: During a study of the Arctic boundary layer. Menemenlis and Farmer used acoustical reciprocal transmissions to obtain line-averaged velocity measurements along 200 m horizontal paths in the mixed layer beneath ice. The present discussion is motivated by a desire to interpret the observed high frequency velocity fluctuations in terms of the advection and evolution of turbulent velocity fine structure. Kaimal et al. (1968) discussed the problem of line-averaging in the context of extending the useful range of sonic anemometers to scales shorter than the acoustic paths. They derived transfer functions that relate measured and ideal one-dimensional power spectra. The present authors investigate the asymptotic behaviour of the spectral transfer functions, as the length of the measuring baseline is increased, and derive analytic expressions. The spectral transfer functions are shown to vary with dimensionless wavenumber and with angle between the measuring baseline and the mean velocity. The analysis is extended to anisotropic and inhomogeneous flows. Finally, some experimental data taken in the boundary layer beneath ice is compared with the theory

Continued development of an IMELDA based voice recognition system for persons with severe disabilities

Abstract: The general design of the authors' speech recognition system is such that the acoustic features are first extracted from the speech signal in the front-end component. Subsequently, these features are passed on to the back-end component where they are compared with stored templates through the technique of dynamic programming. The front-end processing in their speech recognition system is a mel-scale fast-fourier-transform based spectral filter-bank analysis followed by a linear transformation. This linear transformation, which is called IMELDA, was developed and tested and is based on linear discriminant analysis. Comparisons with other systems indicate that it is the `state of the art' for front-end processing in a robust speech recognition system, outperforming other transforms and recognition systems, particularly in degraded speech

Precautions and procedures for precision phase match of microphones

Abstract: Since the publication of the measurement data obtained with the NRC three-port coupler for the precision phase match of condenser microphones, an effort has been made to extend the high frequency performance of the device to cover the phase response of 1/4 inch microphones. The aim is to present current research data, and to discuss some often encountered but less familiar aspects of precision measurement and instrumentation that are necessary to ensure precision phase match

The effects of inhalation of oxygen and carbon dioxide mixtures on noise-induced temporary threshold shift in humans

Abstract: Sixteen subjects breathed either oxygen, carbogen, air with 5% carbon dioxide or air while subjected to 10 min of 100 dB noise and for a further 10 min in order to explore the effect of the various gases on the establishment and recovery of noise-induced temporary hearing threshold shift. Oxygen and carbogen were found to be effective but not different in effectiveness in reducing the establishment of temporary threshold shift suggesting that the role of carbon dioxide in the process is minimal. No evidence was found to suggest that oxygen or carbogen inhalation assists in recovery from temporary threshold shift

Finite element modelling of machinery vibration isolation systems

Abstract: Vibration isolation of ship machinery is needed to achieve low radiated and habitable space noise levels. Shipboard isolation systems can be more difficult to design than similar systems on land due to space restrictions, weight limitations and ship motion considerations. Supporting foundation structures are often lightweight and relatively flexible and can influence the isolation system effectiveness. DREA is enhancing an in-house finite element vibration and strength analysis code VAST to facilitate the analysis of passive vibration isolation systems. The author describes the application of VAST to two problems. The first examines a simple machine decoupled from a flexible foundation structure using sixteen resilient isolators. The second considers the prediction of the natural frequencies of vibration of a helical compression spring isolator

Robust pitch detection for normal and pathologic voice

Abstract: It is known that most of the laryngeal pathologies produce a change in the vocal quality of the patient. The pitch period (To) is significantly affected by these diseases. In most of the pathological voices there are present: (a) large deviations of To and in magnitudes of the peaks of the pitch; (b) deformation of the shape of pitch impulses; (c) abrupt changes in To and the magnitude of the peaks of the pitch; (d) interruptions of pitch generation during sustained vowel phonation-voice breaks; (e) noisy components having a significant amplitude. In order to overcome these difficulties a method is proposed for calculating To by analysis of different domains of the signal