摘要:

For short‐range sound propagation problems, the acoustic energy reaches a remote receiver via a straight direct ray and a ground‐reflected ray and the total pressure at the receiver can be precisely computed considering the geometrical spreading, the atmospheric absorption, and the ground effect [Piercyet al., J. Acoust. Soc. Am.61. 1403 (1977)]. For long‐range sound propagation problems, additional effects have to be considered: mainly, the refraction due to temperature and wind gradients that curve the rays and the turbulence that destroys the coherence between the rays. To evaluate the effect of refraction, a constant linear sound‐speed gradient is assumed. This assumption allows an analytical determination of the curved rays and it also permits the determination of additional reflected rays that may appear in the presence of positive gradients, or of the position of the shadow zone in the presence of negative gradients. The total sound pressure at the receiver is computed by summing up the contribution from all the rays existing between the source and the receiver and, if the receiver is in the shadow zone, the diffraction solution of Berry is used [A. Berry and G. A. Daigle, J. Acoust. Soc. Am.83, 2042–2058 (1988)]. The comparisons between theoretical and experimental results show the accuracy of the proposed model.

ISSN:0001-4966    

DOI:10.1121/1.2027876

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The Federal Highway Administration's “Highway Noise Abatement Criterion” uses the peak hour equivalent sound level for setting limits in highway noise impact studies. In studies conducted by Cavanaugh Tocci Associates, Inc., it has been observed that the FHWA criterion is generally adequate during the day when the traffic mix is such that traffic sound levels are relatively uniform with time, i.e., when the difference between the intrusive sound levels (defined here as the 1 percentile level,L01) and the background sound levels (defined here as the 90th percentile level,L90) are less than 10 dBA. At night, although the FHWA traffic noise criterion remains satisfied, the difference between theL01sound levels produced by truck passbys and theL90sound levels significantly exceed 10 dBA. Once this 10‐dBA margin between theL01and theL90sound levels is exceeded, community response to traffic noise is affected. This large difference between the intrusive and background sound levels seems to explain the “but I can still hear the trucks” syndrome. This experience suggests that highway noise acceptability criteria and environmental impact assessments should also include a limit on the difference between intrusive and background sound levels. Preliminary criterion limits based on studies to date are described.

ISSN:0001-4966    

DOI:10.1121/1.2027936

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

This paper presents a new objective measure for speech quality testing to be used with speech coding systems. This measure is presented in the context of an ongoing 15‐year study of objective measures for speech quality. As part of this research, well over 3000 measures have been evaluated in a study that has done well over a million separate correlation analyses. Included in the study were parametric forms of virtually all commonly used objective measures as well as a large number of new, complex composite measures. The new objective speech quality measure to be presented is a composite measure based on the line spectrum pair (LSP) decomposition of the linear predictive coding (LPC) polynomial. The measure is intended specifically to be used for the design of LPC quantizers for use in a wide variety of speech coding systems. This new measure is the first measure developed in this research that has both very high performance in terms of its ability to predict listener subjective responses as well as the properties necessary to be used explicitly in the design of LPC quantizers.

ISSN:0001-4966    

DOI:10.1121/1.2027980

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Coding (i.e., analysis and resynthesis) of speech signals on the basis of physiological models of speech production mechanisms has received considerable attention during the past several years. One of the reasons for this renewed interest is that the known coding algorithms give unacceptably poor quality of speech at low bit rates (e.g., at 2400 bits/s). A coding scheme that mimics human speech production may have advantages at such low bit rates. Basically, three aspects of speech production need to be modeled. First, the geometry of the vocal and nasal tracts needs to be parametrized. Second, a model must be selected to describe wave propagation in the tract. Finally, the sound sources (vocal cords and turbulent airflow) and their interactions with the tract must be modeled. In this talk the current models being used for each of these categories will be briefly described, and the way in which these models are employed for coding will also be described. Also, the use of such models for text‐to‐speech synthesis will be mentioned. Finally, some examples of speech produced by such models, both from text as well as by analysis and resynthesis of a given speech utterance will be played.

ISSN:0001-4966    

DOI:10.1121/1.2028027

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Fiber‐optic sensors that are imbedded within composite materials could provide structural information during the life of the component, thereby avoiding many of the mechanical failures that today result in death, injury, or environmental accidents. Eventually this fiber‐optic smart structure technology could lead to radical new thinking in terms of engineering and structural integrity monitoring. An overview of this progress will be given, which will include the development and characterization of a number of fiber‐optic strain sensors including afiber‐optic strain rosettefor mapping two‐dimensional strain fields within composite materials, the detection of stress‐inducedacoustic emission, and the development and testing of a multilayered fiber‐optic damage detection system fabricated within a full‐scale compositeaircraft leading edge.

ISSN:0001-4966    

DOI:10.1121/1.2028076

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Research into dynamics and control of large flexible spacecraft has a history of several decades. More recently, application of these techniques to naval structural acoustics has received attention. The dynamic similarity of these two applications is uncanny. This presentation will offer a broad overview of several years of work performed in the Dept. of Aeronautics and Astronautics at MIT in the area of sensor and actuator development for active control of structural dynamics and structural acoustics. Early focus was on piezoceramic actuation of thin metal and composite plates. Current projects include piezoceramic actuation of machinery mounts; piezoceramic actuation of aerodynamic surfaces; piezoceramic and electrostrictive actuation of optical components; piezoceramic actuation of specific traveling wave components in bending; piezeoceramic actuation and sensing of truss structures; customized spatially distributed strain sensing with PVDF film; low stiffness spacecraft mounting systems with PVDF film actuation; and basic comparison and classification of a range of solid‐state actuation possibilities.

ISSN:0001-4966    

DOI:10.1121/1.2028100

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The design and development of piezocomposites for use as the actuating device in an underwater acoustic control system coating will be discussed. Both flexible piezoceramic and 1–3 piezocomposite designs are explored as actuator candidates in the thin‐walled polymer matrix encapsulant coating. The actuators will be presented in single layer form for the absorption of normally reflected acoustic pressure waves. A bilaminate design will be shown for the absorption of both the normally reflected and transmitted acoustic waves. Experimental measurements will be used for performance comparison of different composite and lamination designs.

ISSN:0001-4966    

DOI:10.1121/1.2028105

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Neural networks are a general class of computational models that can be used to model a variety of music perceptual tasks. An important issue in designing a neural network is the representation of input. The choice of representation can influence the network's trainability, its plausibility as a perceptual model, and its ability to generalize to other musical tasks. Networks that have been trained either to classify musical chords or to identify musical pitch are described. Four approaches to representation are examined. The simplest is a tone‐chroma notation in which there are 12 possible input nodes, one for each tone of the Western chromatic scale. Two approaches, a harmonic and subharmonic template, are motivated by theories of complex pitch perception. Input nodes are quantized into pitch‐class categories of the Western chromatic scale, and incorporate the notion of pitch height as well as tone chroma. In the fourth approach, each input node represents a frequency bin with a one‐third semitone bandwidth. This enables coding of input frequencies that are mistuned with respect to the standard tuning of Western music.

ISSN:0001-4966    

DOI:10.1121/1.2028111

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Questions concerning the developmental timetable for the acquisition of musical knowledge have been studied very little. This study of infants suggests a precocious onset of musical scale knowledge, an important aspect of music cognition, as findings indicate that infants better perceived mistunings in native than in nonnative scales. Six‐ and 12‐month‐olds were tested in noticing increases in the frequency of a randomly selected note in a melody based on the Western major scale (most common Western scale based on the semitone), the Western augmented scale (infrequently used Western scale but also based on the semitone), and the Javanese pelog scale (nonnative scale not based on the semitone). An operant head‐turn procedure was used in which the well‐tuned version of each melody was played repeatedly through a loudspeaker, and the infants learned to turn their heads toward the speaker in anticipation of a visual reinforcer when they noticed a frequency change in one of the melody notes. The 12‐month‐olds' performance was better on the major scale than on either the augmented or pelog scales. In contrast, the 6‐month‐olds' performance was better on both the major and augmented scales than on the pelog scale, and their performance was similar on the major and augmented scales. These findings suggest that substantial musical acculturation occurs as early as 6 months of age and that infants may proceed from acquisition of knowledge of the semitone as a basic structure of Western music to acquisition of more specific knowledge of the major scale by 12 months of age.

ISSN:0001-4966    

DOI:10.1121/1.2028112

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

When considering nonlinear wave propagation through a medium, it is important to consider which linear attenuation mechanisms significantly affect wave profiles. Specifically, it must be asked whether a particular physical attenuation is sufficient to prevent the overturning of finite‐amplitude waves. Thermoviscous dissipation, however small, will always prevent such overturning, but relaxation effects alone do not necessarily ensure single‐valued solutions. In this paper, the attenuation effects of a relaxing medium are investigated. The model equation considered contains two parameters [D. G. Crighton, Ann. Rev. Fluid Mech.11, 11–33 (1979)] related to a characteristic relaxation time and to the difference between equilibrium and frozen sound speeds. A method using intrinsic coordinates is described as a means of investigating the phenomenon of overturning. This is then applied to the case of a relaxing medium. In this way, the set of parameter values is divided into those for which single‐valued solutions are obtained, and those for which overturning occurs. The latter case corresponds to the physical situation of normally insignificant thermoviscous dissipation becoming locally as important as the relaxation effects.

ISSN:0001-4966    

DOI:10.1121/1.2028116

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP