摘要:

The source spectrum level density of wind‐generated noise has been deduced from ocean measurements, laboratory experiments, and theoretical studies in the past 25 years. Selected contributions are reviewed and the results are compared. Since the source level results compare favorably, at least in deep water, an average source spectrum level density as a function of frequency and surface wind speed is proposed for use in noise models. The differences between the dipole and “rocking” dipole source directivity patterns is discussed and wind‐generated noise modeling issues are addressed. There seems to be little agreement on the underlying physical mechanisms of wind‐generated noise. The question of what information would be added to the source spectrum level densities if a theory for the underlying physical mechanisms were known is also addressed.

ISSN:0001-4966    

DOI:10.1121/1.2022685

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

The characteristics of underwater noise in the ocean generated by precipitation are important to weather forecasters and oceanographers since they permit the detection and measurement of rain over the ocean by remote (i.e., buoyed or bottom‐mounted) acoustic sensors. We have recently observed the character of the underwater noise generated by rain, hail, and snow. The spectrum of rain noise, for wind speeds below 1.5 m/s, shows a peak of 13.5 kHz with a sharp cutoff on the low‐frequency side and a gradual falloff (7 dB per octave) on the high‐frequency side. Stronger winds smear the peak. Hail spectra show a peak at 3.0 kHz with a gradual (roughly 11 dB per octave) falloff on both sides. The spectrum of snow noise is unique. Our instrumentation permitted the measurement of the drop (or stone) size distributions in the precipitation. These findings will enhance the art of remote acoustic sensing in oceanograpy. [Work supported by: Supply&Services Canada; Institute of Ocean Sciences, Sidney, BC, Canada; Atmospheric Environment Service, Toronto, Canada; and Department of National Defence, Canada.]

ISSN:0001-4966    

DOI:10.1121/1.2022740

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Low‐frequency ambient noise sources observed in the Arctic are discretely located in space and time. With a large number of events per unit area per unit time, the total number of contributions to any one observation grows with horizontal range but also shrinks in intensity inversely with range. This standoff therefore suggests that limits on observed ambient noise are set by basin bathymetry and/or by sound absorption. In one useful model we find the source spectral density typical of low‐frequency events is changed via the basin by anf2shaping at frequencies below, and by anf−1shaping at frequencies above a characteristic frequency. [Work supported by ONR.]

ISSN:0001-4966    

DOI:10.1121/1.2022803

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Impulsive noise, either in the military or industrial setting, rarely occurs without some substantial background noise. This paper reviews a series of animal experiments which show synergistic interactions between relatively “safe” continuous and impulsive noise. In all the experiments, chinchillas were either exposed to (1) 60 min of background noise (either 2–4 kHz or 0.5–1 kHz) at levels ranging from 95 to 89 dB; (2) 50 spark discharge‐generated impulses with peak sound pressure levels ranging from 158 to 137 dB andAdurations of 32 to 64 μs; (3) various combinations of (1) and (2). The animals' hearing was measured immediately after the exposure, and at regular intervals over a 30‐day period. After 30 days, the cochleas were analyzed for losses of sensory cells. The results show that certain combinations of individually “safe” impulse and continuous noise can (1) produce a synergistic interaction; (2) that these interactions behave systematically as either the level of the impulse or the continuous noise is reduced; and (3) that the interaction effect is enhanced as the frequency spectra of the two noises begin to overlap. The results of the experiments will be discussed in terms of the mechanisms of noise‐induced hearing, implications for measurement of noise environments loss, and the implications for public health standards. [Work supported by NIOSH.]

ISSN:0001-4966    

DOI:10.1121/1.2022854

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

The main purpose of this study was to produce additional information on the connections between the temporary hearing thresholds, body upright posture sway, and cardiovascular changes induced by complex exposure conditions. Seven healthy male students were exposed consecutively five times to mere noise, to mere whole body vibration, and simultaneously to noise and vibration at 20 °C. The noise categories were: (1) no noise and (2) noise of 90 dBA. The categories of low‐frequency whole body vibration (Zaxis) were: (1) no vibration, (2) vibration within the range 4.4–5.6 Hz, (3) vibration within the range 2.8–5.6 Hz, (4) vibration within the range 2.8–11.2 Hz, (5) vibration within the range 1.4–11.2 Hz, and (6) sinusoidal vibration with a frequency of 5 Hz. The (rms) acceleration in all the vibration models was 2.12 m/s2. The TTS2values at 4 and 6 kHz increased as a result of simultaneous exposure to noise and vibration significantly more than as a result of exposure to noise alone. The means of the sway variances in theXandYdirections at 0.1 Hz and within the range 0.06–2.00 Hz increased only when the vibration in the noise‐vibration combination was a sinusoidal one. The changes in the heart rate,R‐wave amplitude, blood pressure, and the haemodynamic index scores also depended on the bandwidth of the vibration, the number of consecutive exposures, and on whether the subjects were simultaneously exposed to noise in addition to vibration. [Work supported by The Academy of Finland.]

ISSN:0001-4966    

DOI:10.1121/1.2022904

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

We discuss the design of a text‐to‐speech synthesizer, which accepts any type of English text as input, and creates an appropriate speech signal as output. Effective algorithms for converting text to sound must make use of intermediate data structures that systematically encode the degrees of freedom available to speakers of the language being synthesized. These data structures are an engineering approximation to what linguists callphonological representations; we will call them “P‐structures.” Any TTS system must: (1) define its version ofP‐structures; (2) design and implement algorithms for transforming input text intoP‐structures; (3) design and implement algorithms for transformingP‐structuresinto sound. Task ♯1 is mainly a problem in applied linguistics; task ♯2 can best be seen as applied AI; task ♯3 is an application of phonetics and signal processing expertise. Because of the interdependence of approximate solutions in different portions of the system, integration of the various parts is a non‐trivial problem. We will analyze an example of a TTS system, showing how these problems were handled in building and combining its numerous pieces. Finally, we point out some areas where better solutions are needed, and suggest how to find such solutions.

ISSN:0001-4966    

DOI:10.1121/1.2022951

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

With a subsystem designed to extract meaning from written Esperanto being added to the speech synthesis system of Japanese generated in the semantic/syntactic base [S. Sato and H. Kasuya, J. Acoust. Soc. Am. Suppl. 173, S5 (1983)], we present an overview of this translation‐synthesis system including a knowledge base editor for implementing linguistic information needed. Allowing a wide range of data modification and file manipulation operations, the frame editor can edit on a frame/slot basis the rules and dictionaries used in parsing Esperanto and generating Japanese. The main portion of the knowledge base is occupied with descriptions about case structures, selectional restrictions, hierarchial relations among items, etc. for detecting anomaly and ambiguity of a given Esperanto sentence. The semantics gives to the meaning a case frame expression, from which the sentence generator produces a surface form with some trimming with phonological and accentuation rules. The synthesis program further converts the surface into acoustic parameters, rendering a time series of control parameters for the terminal analog synthesizer.

ISSN:0001-4966    

DOI:10.1121/1.2023007

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

We examined the applicability of DP matching as a tool for evaluating methods for connecting synthesis units. In speech synthesis by rule, speech quality depends greatly on how to connect synthesis units (e.g., syllables). The most widely used method is to use human ears. Although it is justifiable as the final judgment, it is time‐consuming as well as fairly listener‐dependent. The method proposed here is to use the amount of residual errors of DP matching, which has been widely known in speech recognition. When we confront the problem of selecting parameters of a particular connecting method, we record words naturally spoken (presumably continuous) and then operate DP matching between the natural speech and synthetic speech. The parameter set that produces the least amount of residual error is selected. We devised DP matching particularly suited to this purpose. We found that the optimized parameters with this method agreed well with those obtained with human ears and believe that this proposed automated method is applicable as a substitute of human ears for sizable classes of evaluation problems.

ISSN:0001-4966    

DOI:10.1121/1.2023055

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

The acoustical diffusing properties of flat, mono, and bicylindrical surfaces, alternating absorptive and reflective panels, and a wide variety of reflection phase grating diffusors (RPG) will be discussed. Experimental TEF measurements including energy‐time, energy‐frequency, time‐energy‐frequency, and polar angle‐energy‐frequency curves plus theoretical Kirchhoff modeling calculations will be presented. A new control room design incorporating a reflection‐free zone (RFZ), in the front half of the room, and a diffuse zone, in the rear half of the room created with RPG diffusors, will be described and documented. The RFZ minimizes the speaker boundary interference over a wide volume surrounding the mix position. The RPGs provide a diffuse sound field which enhances the perception of spatial textures and helps maintain the stereo perspective across the entire width of the mixing console and in the rear of the room. The RFZ/RPG design minimizes frequency coloration, image shifting, and provides accurate stereo imaging.

ISSN:0001-4966    

DOI:10.1121/1.2023058

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Physically small rooms are often erroneously analyzed and measured according to the classical statistical acoustical equations and techniques. Evidence is presented herein to support the position that a truly diffuse reverberant field does not exist in such spaces at a level above that of the ambient noise.

ISSN:0001-4966    

DOI:10.1121/1.2022640

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP