摘要:

This paper discusses modification of acoustic signals by two‐dimensional (time/frequency) processing of the short‐time Fourier transform. This approach is suggested by time/frequency processing in the human auditory system, and is appropriate for signals such as speech and music. Time/frequency processing has two potential advantages (1) the signal processing domain is similar to the perceptual domain, so that signal modifications are related to perceived changes, and (2) visible displays of the short‐time spectrum (spectrograms) can be used as an aid in developing and evaluating specific processes. The mathematical basis for time/frequency processing is developed, and two examples are discussed removal of broadband background noise in old recordings and compression and expansion of speech for transmission through noisy channels. [Work supported by ARPA.]

ISSN:0001-4966    

DOI:10.1121/1.2015754

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Various stages in the development of computer models to support research in acoustics will be considered. Emphasis will be placed on the use of interactive computer graphics to provide increased comprehension and thus new insights into the nature of the experimental data. Specifically, problems of image enhancement will be discussed as they relate to visual perception of multidimensional models where the number of dimensions necessary to achieve new insights has been extended beyond three. A film summarizing some of the results achieved to date will be shown.

ISSN:0001-4966    

DOI:10.1121/1.2015761

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The role of the audio engineer in the design of a professional sound reinforcement system is becoming a more and more difficult and complicated one with the advent pre‐equalized speaker systems that must operate at given sound pressure levels before feedback in less than ideal acoustical environments. Possibly the most feedback critical and important speaker systems in “the house” are the monitors—the speakers by which the performer judges himself. The systems engineer must be able to guarantee the acoustic output level over an ever increasing bandwidth approaching the limit of human hearing. Special emphasis must be placed on the high‐frequency response if the system is to be useable for monitoring acoustic guitars and other instruments with high‐frequency content. All this must be accomplished with regard to speaker “break‐up,” efficiency, cost, and complexity. For these reasons a two‐way system using a vented box enclosure seemed to offer an optimum solution for monitoring requirements.

ISSN:0001-4966    

DOI:10.1121/1.2015767

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

As part of the federal government's role to protect Canadians from the adverse effects of noise, an assessment of noise hazard and control has recently been completed and will be published. It is planned to use this document, together with further studies to establish criteria on the auditory and nonauditory effects of noise. Community noise studies in Canada have been assessed as part of this work, particularly for their usefulness toward government regulations and other noise control activities. Descriptions of community noise measurements in Alberta, British Columbia, and Ontario will be amongst those discussed. Emphasis will be given to instrumentation, techniques of analysis and reporting, and temporal and spatial sampling used.

ISSN:0001-4966    

DOI:10.1121/1.2015771

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Numerous small cities and towns in New Jersey have been preparing Natural Resource Inventories (NRI). These NRI's document the present environmental, sociological, historical, and other facets, of the communities' quality of life. One parameter in the NRI is sound quality. A comprehensive survey to document sound levels in residential, commercial, industrial, and other land‐use areas is necessary. The cost to accomplish these surveys using sophisticated equipment and trained personnel can be quite prohibitive. This is especially true if the community is large. In three New Jersey communities an alternate approach was used. Through a series of public meetings, community residents were made aware of the NRI and particularly the sound quality aspects. Volunteers were trained in the use of sound level meters and a simple measurement procedure similar to the SAE method for measuring construction site noise. The data resulting from measurement made by the volunteers allowed a mapping of sound levels in the community. The mapping provides guidance to planners and may aid in the development of a national community noise ordinance sensitive to the existing sound quality of the township. Typical results are presented for one township, in New Jersey. [Work supported by EPA.]

ISSN:0001-4966    

DOI:10.1121/1.2015776

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

A unique experiment has been conducted to identify the dependence of variations in truck noise emission measurement data upon changes in vehicle performance and sound propagation properties. A comparison of data measured at different sites and at different times at the same site by previous investigators [e.g., J.E. Piercyet al., “Mechanisms Causing Variability in Noise Testing of Light Motor Vehicles,” NRC, Ottawa, Ontario (1976)], has shown a variability in the mean maximumA‐weighted sound pressure level of up to 4 dB. Little similar data is available for medium and heavy‐duty trucks. In this experiment, preliminary data have been obtained for one gasoline and two diesel‐fueled trucks performing SAE J366b drivebys, simulated drivebys, and idle‐maximum idle runups. The results obtained to date, as part of a one year series of tests, are presented as a function of several of the various performance and environmental variables.

ISSN:0001-4966    

DOI:10.1121/1.2015778

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

An obstacle existed in the past to simulating distributed parameters by means of a Tee‐network. This obstacle was the requirement to represent impedance functions having negative slope, such as — cosecantwl/c. Such a representation is not possible with passive elements. However, this can now be easily done in several ways. One way is to use lumped impedance elements combined with active circuits, to produce negative components. Another way is to use a desk‐top calculator in conjunction with an equivalent‐circuit analysis program that uses lumped elements, positive or negative. People who like circuits obtain a certain additional insight from this circuit approach, an insight which is not given by the usual analysis methods. The method is applicable to electromechanical transducer simulation, vocal‐tract simulation, and woodwind instrument simulation. Some graphical solutions to a transducer problem, automatically obtained in a few minutes, will be shown.

ISSN:0001-4966    

DOI:10.1121/1.2015786

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

An approach is presented to analyze the transient behavior of a piezoelectric transducer in a pulse echo system using FFT algorithms. The radiation field is described using impulse response and Fourier integral techniques [P.R. Stepanishen, J. Acoust. Soc. Am.60, S100 (A) (1976)] whereas the transducer is described via the use of a distributed parameter model which includes piezoelectric losses. The approach can be used to readily evaluate the near field time dependent pressures which result from short pulse electrical excitations of a transducer. The receiving response of the transducer for the short pulse excitation can then be readily evaluated for the case of idealized scatterers in the acoustic near field. Extensive numerical results are presented for the near field pressures and receive voltages which result from the short pulse excitation of a piezoelectric disc operating in the thickness mode. For pulse durations which are less than the travel time across the disc, a multipulse structure is clearly observed in both the field pressures and the receive voltages. [This work was supported by NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2015789

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

At 18 to 19 days of incubation the heads of chick embryos were removed from the egg. Three groups of subjects were formed by injecting a silicone ruber adhesive into either the left, right, or both ear canals. A fourth nontreated group acted as controls. Embryos were returned to the incubator and allowed to hatch normally. Between 24 and 72 hours the chick neonates were anesthesized, the ear plug(s) removed, and the animals were mounted in a head holder. A sound‐probe tube system was sealed over the left and right tympanic ring. The neostriatum was exposed to reveal the optic tectum and a concentric electrode was inserted into the right Mesencephalicus Latoralis pars Dorsalis (MLD). Evoked‐response thresholds for test frequencies between 0.125 and 5.0 kHz and the relation between stimulus SPL and evoked‐response amplitude at 0.25, 0.5, 1.0, and 2.5 kHz were measured in every subject for left‐ and right‐ear stimulation. The results indicate no differences in threshold sensitivity between all sound‐deprived and control animals. However, the relation between SPL and evoked‐response amplitude at 0.25 and 0.5 kHz was significantly different between deprived and control subjects. The results indicate that an early conductive hearing loss results in abnormal auditory development which is probably located in the nervous system. [Work supported by NSF.]

ISSN:0001-4966    

DOI:10.1121/1.2015797

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

A two‐branch artificial ear was compared with two four‐branch artificial ears (Zwislocki couplers). Overall results from the two coupler types were very similar. The equivalent volumes of the couplers were evaluated by comparing the levels developed in these couplers with the level developed by the same signal in a 2‐cc cavity. From 100 to 5000 Hz the equivalent volume of the two‐branch coupler was slightly less than that of the four‐branch couplers, the difference never exceeding 0.1 cc. The acoustic damping provided by the couplers was compared by measuring the amplitude of reactance resonances observed when the couplers constituted the volume of the resonator (a situation analogous to the acoustic system operating when vented earmolds are used). In the 400–700‐Hz range, resonances developed in the two‐branch coupler were 2–3 dB less damped than the analogous four‐branch coupler resonances. In the 2–3‐kHz range the damping of the couplers was approximately equal. This evidence suggests that the two‐branch coupler provides less damping of typical vent related resonances than does the real ear. [Work supported by NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2015806

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP