Characteristics Of Sound Sources Research Articles

Distance judgments of nearby sources in a reverberant room: Effects of stimulus envelope

Localization was measured for nearby sources with abrupt or slow rise/fall times in a reverberant space. A recent model of distance perception [A. W. Bronkhorst and T. Houtgast, Nature 397, 517–520 (1999)] suggests that perceived distance is computed from the room impulse response. The model assumes that energy in the onset of the impulse response (primarily from the direct sound, varying with distance) is compared to late energy (primarily from the reverberation, roughly independent of distance). However, other results suggest that subjects are poor at deconvolving transfer function and sound source characteristics [Rakerd et al., J. Acoust. Soc. Am. 106, 2812–2820 (1999)]. Taken together, these results suggest that subjects cannot use the transfer function, but estimate source distance from some statistic closely related to that proposed in the model (e.g., the ratio of initial to late energy in the total waveform at the ear). For impulsive sounds, such a simpler statistic yields results similar to those of the model; however, distance judgments would be significantly degraded for sources with slow onsets. However, subjects were equally good at judging distance, independent of characteristics of the stimulus envelope. [Work supported in part by AFOSR Grant No. F49620-98-1-0108.]

Physical and perceptual modeling of sound-source radiation

Radiation characteristics of sound sources are now considered important when reproducing the signal of a musical instrument or, more generally, when controlling a virtual auditory scene. Both applications have raised the need for analyzing, modeling, and synthesizing the radiation behavior of sound sources. The first part describes a general method for the reproduction of arbitrary radiation patterns with digitally controlled loudspeakers arranged to form a three-dimensional array. In order to evaluate the performance of the synthesis method, this section presents possible definitions of similarity criteria based either on a physical or a perceptual approach. In the second part, perceptual features are investigated based on the analysis of musical instruments or listening tests conducted with elementary radiation patterns such as the first spherical harmonics. The perceptual analysis is conducted first with the help of classical acoustic cues used in room acoustics, and second by analyzing the possible consequences of directivity characteristics on stream segregation mechanisms involved in auditory scene perception. The final part presents ongoing research on the reproduction of salient directivity cues of different musical instruments, as well as the voice.

The characteristics of sound source of aeolian sound generated from the wake behind the bent round bar in uniform air flow

The characteristics of sound source of aeolian sound generated from the wake behind the bent round bar in uniform air flow

An acoustic integration model (AIM) for assessing the impact of underwater noise on marine wildlife

In recent years there has been a heightened awareness of the environmental impact of noise, especially man-made noise, on marine wildlife. The National Environmental Policy Act (NEPA), Executive Order 12114, The Endangered Species Act, The Marine Mammal Protection Act, and the Coastal Zone Management Act each provide for varying levels of regulation and control in protection of the environment and marine wildlife. In order to assess the environmental impact of a sound source, one must predict the sound levels that any given species will be exposed to over time in the locale of the source’s radiated field. This is a three-part process involving (1) the ability to measure or predict an animal’s location in space in time, (2) the ability to measure or predict the sound field at these times and locations, and finally, (3) integration of these two data sets so as to determine the net acoustic impact of the sound source on any specific animal. This paper describes a modeling methodology for accomplishing this task. Model inputs required to specify the acoustic environment, animal distribution and behavior, and sound source characteristics are discussed in detail. The AIM model output capabilities are described together with topical examples.

ACOUSTIC CHARACTERISTICS OF PULSED SOUND SOURCES OF VARIOUS TYPES/ĮVAIRIŲ TIPŲ IMPULSINIŲ GARSO ŠALTINIŲ AKUSTINĖS CHARAKTERISTIKOS

The paper examines the acoustic characteristics of explosion-type pulsed sound sources of four types. These include a Calibre 8 sound gun, a start gun, a Calibre 16 hunting gun, and a toy gun. The latter was included both because of its short pulse duration and for comparison purposes. Correct selection of a source is very important because it largely determines the results of acoustic measurements. Certain requirements are set for a sound source. In order to concentrate as much energy as possible at the given moment, the signal bandwidth-duration product must be as large as possible. The range frequencies to be excited depend on the pulse duration. The latter also determines whether interference phenomena will occur in the room and whether individual reflections will merge. The experiments were conducted in a room of 12 m2. The distance between the microphone and the pulsed sound source was 1 m. The structure of reflections depends on the pulse by means of which the sound field is excited. The smallest number of reflections is generated by a sound source. During a 20 ms experiment, the amplitudes of these reflections almost coincided with the direct sound amplitude. A sound gun emits more sound energy than other pulses. When the sound field is excited by means of a start gun and a hunting gun, the reflection structure, by amplitude, is very different from that produced by a sound gun. A dense reflection structure is formed by a toy gun but it emits less energy. The structure of reflections generated by a hunting gun is acceptable but its shots are very unstable, which is a major drawback in an experiment. The shots from a sound gun differ only by about 0.1% among themselves by amplitude, ie they are sufficiently stable. Among the four sound sources, the best reflection structure is produced by a sound gun. A sound gun is characterised both by the longest pulse duration (about 0.55 ms) and the highest levels of energy emitted. The pulse duration of the rest three guns is almost equal and is about 0.15 ms, ie is 3.6 times shorter than that of a sound gun. The forms of signals emitted by these sound sources are also very different. The spectrum of a sound source was established on Fourier transformation basis. The spectrum is largely dependent on the type of a gun by means of which the sound field is excited. The maximum width of the spectrum generated by a sound gun occupies almost two octaves, from 500 to 2000 Hz, and the radiation in this range is quite uniform. The spectra of a start gun and a hunting gun are similar but these guns emit less sound energy than a sound gun. The structure of reflections generated by them is also quite different. A toy gun radiates energy in a less narrower band, the width of which occupies about a half of octave, with a maximum at 2000 Hz. This is not very good because too small quantities of low- and medium-frequency sound energy are radiated.

ACOUSTIC CHARACTERISTICS OF PULSED SOUND SOURCES OF VARIOUS TYPES

Summary The paper examines the acoustic characteristics of explosion-type pulsed sound sources of four types. These include a Calibre 8 sound gun, a start gun, a Calibre 16 hunting gun, and a toy gun. The latter was included both because of its short pulse duration and for comparison purposes. Correct selection of a source is very important because it largely determines the results of acoustic measurements. Certain requirements are set for a sound source. In order to concentrate as much energy as possible at the given moment, the signal bandwidth-duration product must be as large as possible. The range frequencies to be excited depend on the pulse duration. The latter also determines whether interference phenomena will occur in the room and whether individual reflections will merge. The experiments were conducted in a room of 12 m2. The distance between the microphone and the pulsed sound source was 1 m. The structure of reflections depends on the pulse by means of which the sound field is excited. The smallest number of reflections is generated by a sound source. During a 20 ms experiment, the amplitudes of these reflections almost coincided with the direct sound amplitude. A sound gun emits more sound energy than other pulses. When the sound field is excited by means of a start gun and a hunting gun, the reflection structure, by amplitude, is very different from that produced by a sound gun. A dense reflection structure is formed by a toy gun but it emits less energy. The structure of reflections generated by a hunting gun is acceptable but its shots are very unstable, which is a major drawback in an experiment. The shots from a sound gun differ only by about 0.1% among themselves by amplitude, ie they are sufficiently stable. Among the four sound sources, the best reflection structure is produced by a sound gun. A sound gun is characterised both by the longest pulse duration (about 0.55 ms) and the highest levels of energy emitted. The pulse duration of the rest three guns is almost equal and is about 0.15 ms, ie is 3.6 times shorter than that of a sound gun. The forms of signals emitted by these sound sources are also very different. The spectrum of a sound source was established on Fourier transformation basis. The spectrum is largely dependent on the type of a gun by means of which the sound field is excited. The maximum width of the spectrum generated by a sound gun occupies almost two octaves, from 500 to 2000 Hz, and the radiation in this range is quite uniform. The spectra of a start gun and a hunting gun are similar but these guns emit less sound energy than a sound gun. The structure of reflections generated by them is also quite different. A toy gun radiates energy in a less narrower band, the width of which occupies about a half of octave, with a maximum at 2000 Hz. This is not very good because too small quantities of low- and medium-frequency sound energy are radiated.

An investigation of the characteristics of impact sound sources for impact sound insulation measurement

At the assessment of the impact sound insulation of a construction, a standard tapping machine is used as sound source. However, the current standard tapping machine has been criticised especially for measurement of wooden joist floors since the sounds generated by a tapping machine differ from those generated by actual footfall. This study has investigated the waveform and frequency spectra of human footfall (walking, running and jumping), of sand balls, sand bags and dropped tires, and of the standard tapping machine. It is shown that the frequency spectra differ between the standard tapping machine and actual footfall, especially at low frequencies. Results from other excitation sources such as a sand ball falling from a certain height showed concordance with actual footfall. This means that a sand ball drop as an impact source provides a better representation of actual human footfall than the standard tapping machine.

EXPERIENCES WITH VARIOUS CONFIGURATIONS OF MICROPHONE ARRAYS USED TO LOCATE SOUND SOURCES ON RAILWAY TRAINS OPERATED BY THE DB AG

This paper gives an overview of the results and conclusions from measurements made with various configurations of microphone arrays designed to locate sound sources on trains operated by the Deutsche Bahn AG at speeds up to 280 km/h. These arrays comprised one- and two-dimensional arrangements of up to 29 microphones. The characteristics peculiar to microphone arrays will be mentioned only briefly here, because the theoretical background of array measurements is available in other publications. Within the context of the present paper, the sound sources located are those generated mechanically, principally by wheel/rail interactions, and those produced by aerodynamic fluctuations. In addition, noise radiation from cooling systems was also measured during passages of the trains. Examples are given of results obtained with different kinds of arrays during pass-bys of dedicated ICEs and goods trains. These examples demonstrate the usefulness of array measurements for producing detailed information pertaining to the characteristics of individual sound sources. With respect to these individual sound sources particularly on moving vehicles, array technology provides a much more efficient and capable tool for investigating these sources than does the more conventional technique employing single microphones.

A method for characterizing aerodynamic sound sources in turbomachines

A method based on Weidemann’s acoustic similarity laws [1] was used to investigate the aerodynamic sound generated by a partially ducted centrifugal pump rotor. The primary objective of the method was to determine the spectral characteristics of the sound source by isolating the effects of acoustic phenomena such as duct resonances or sound reflections. Pump-radiated sound pressure spectra were measured for different impeller rotational speeds, keeping the operating condition constant. The spectra, assumed to be expressed as the product of a source spectral distribution function and an acoustic frequency response function, were then decomposed into a product form following a computer-implemented algorithm. The method was successful in accurately determining the spectral distribution of the broadband aerodynamic noise generating mechanisms involved and that of the acoustic frequency response of the system. The absolute levels of the source function and the acoustic function were established by assuming that, over a limited low frequency range, the average gain of the frequency response function is unity so that comparisons between different pump operating conditions could be made. The source spectral distribution was found to be independent of the microphone location and the acoustic loading. When applicable, this method therefore allows the characterization of aerodynamic sound sources by measuring ordinary sound pressure spectra, at any one point around the source, without having to isolate the source from the system. The source characterization method was instrumental in the study of sound generation by rotating stall presented in a previous publication [2].

Ray-tracing analysis of auditorium acoustics for the Macintosh

An enhanced version of a previously presented geometrical ray-tracing program for the Macintosh [M. Rieffel and E. C. Everbach, J. Acoust. Soc. Am. 91, 2373(A) (1992)] will be demonstrated. The program accepts input files of auditoria created in any of several popular CAD programs that export standard DXF formats, displaying the auditorium in 3-D projection. The user specifies the surface absorption coefficients of all internal surfaces and the placement and characteristics of sound sources. The user also specifies an arbitrary ‘‘monitor’’ plane passing through the hall, each point of which will be a receiving location in the subsequent simulation. When the simulation is run, rays are propagated between source and receiver, allowing the computation of an echogram for each point in the monitor plane. In this way users can discover focusing, dead spots, or late reflections at specific locations in a proposed hall design. The program is available for consultant or instructor use, and will be demonstrated during the session.

Structure-borne sound power through multiple contact points between machines and supporting structures

The structure-borne sound emission from machines through multiple contact points is highly influenced by the extent of coupling between these points. When the machine is unconstrained (i.e., disconnected from the supporting structure) the coupling can be assessed by comparing the point and transfer mobilities of the machine. Once connected however, account must be made too of the force distribution amongst the contact points. While the forces themselves at the points are sensitive to the structural characteristics of the particular installation, their distribution, which is most readily described by the ratios of the contact point forces, may be less sensitive. Using combinations of real and theoretical installations, force distributions have been investigated. Studies have also been undertaken on the estimation and approximation of the force ratios and their effect on the estimate of the total active power from the machine to the supporting structure. It will be shown that this has application to the characterization of structure-borne sound sources.

Use Of The Source Descriptor Concept In Studies Of Multi-Point And Multi-Directional Vibrational Sources

A study of the influence of multi-point and multi-component coupling on structure-borne sound source characterization has been carried out. In particular, the effects of cross-coupling between different components of excitation and motion at a contact point have been examined. Theoretical results are supported by results of experiments on real machines, a family of fan units. The significance of the various components of excitation and motion is interpreted in terms of the source descriptor, a quantity defined on a power basis. It is shown that measured source descriptors associated with force and moment can be equally important and, accordingly, none can be excluded a priori. It is also shown that multi-point and multi-component coupling can have a profound influence. The ability of the source to impart vibrational power at global anti-resonances of the source structure is demonstrated. In addition, this ability is spectrally transposed to a higher frequency range than that predicted from a single point, single component analysis.

Evaluating the importance of source directivity, frequency, and phase response in the auralization of sound system designs

Acoustic sources for the sound systems, i.e., loudspeakers have unique and individual characteristics such as amplitude frequency response, phase frequency response, transient response, and directivity. Consideration of these characteristics is as important a part of sound system auralization process as the calculation of precise room responses, such as diffusions and diffractions, in architectural acoustic oriented auralization systems. However, no statistical studies have been made on this subject so far. In this study, the importance and advantage of considering sound source characteristics as a transient response are revealed and a practical impulse response calculation algorithm that is accurate enough and practical for auralization of sound system designs is described.

Approach to speaker‐independent connected word recognition for telephone application

This paper describes a new speaker‐independent connected word recognition method for telephone use. For this recognition, it is necessary to deal with the following four problems: utterance speed variations in speakers; spectrum variations caused by a speaker's sound source and vocal tract characteristics; interference between words in continuous speech; and telephone circuit noise. For the first problem, a new nonlinear time division method is proposed using the spectral transition ratio. The result shows a phoneticlike segmentation. This method is more effective than DTW (dynamic time warping) in the case of speaker‐independent systems. For the rest of the problems, a set of features will be used that give a maximum recognition accuracy, for example, the spectral local peak, the ratio between the higher and lower frequency components, and spectral transition vectors. The method is quite robust in the face of spectral changes because the features cooperate with each other. This method shows a high perfor...

Localization of coherent and incoherent sound sources via an optimization process

The problem of the localization and characterization of sound sources is discussed, for the case of a set of monopole sources, starting with the analytic expressions describing the field in combination with a gradient method for the optimization process. To locate the sources, three measurement variables are used: the 3-D vectorial active intensity, the normal active intensity, and the mean-square pressure. Simulations for three emitting sources, aimed at predicting their positions and spectral densities, are made. The minimum number of measurement positions that lead to convergence of the algorithm is investigated. The agreement between prediction and reality is good even when the sources are coherent. In parallel, the impact of the choice of measurement variable on the precision of the results is studied. In the very near field of the source, it is found that identification via 3-D intensimetry requires a significantly lower number of measurement positions than does that via normal intensity or mean-square pressure.

Computer simulation of frequency response in room considering directivity characteristics of sound source

Computer simulation of frequency response in room considering directivity characteristics of sound source

Characterization of structure-borne sound sources: The source descriptor and the coupling function

An introductory, theoretical study for characterization of structural acoustic sources has been carried out. The concept source denotes any active structure with unknown internal elementary source mechanisms and unknown internal transmission paths from generation to the contact points with the receiving structure. An alternative description of the power transmission from the source to the receiver is presented in the case of one component of motion and one contact point. A general source parameter called the source descriptor is introduced. This parameter is a function of source data only. It is proportional to power and involves both the internal vibration of the source and its mobility at the contact point. From experimental measurement series, it can be emphasized that the velocity of the free source is a suitable and manageable quantity for describing the internal vibration of many structure-borne sound sources. The active power transmitted from the source structure to the receiving one is found to be the product of the source descriptor and a dimensionless function called the coupling function. This function illustrates the dynamic properties of the source-receiver interface.

Standard deviation in the power measurement of sound sources by the free field method

Standard deviation in sound power measurements made by the free field method (ISO 3745) is discussed. The authors numerically investigated the relationship between the standard deviation and the directivity characteristics of sound sources. The standard deviation of the sound power of sources as measured according to ISO 3745 increases as the directivity of the sources becomes sharp. However, the standard deviations are almost constant when the directivity characteristics approximate a cos 2 n θ function with n

Localization of coherent and incoherent sound sources via an optimization process

The problem of the localization and characterization of sound sources is tackled, for the case of a set of monopole sources, starting with the analytic expressions describing the field in combination with a gradient method for the optimization process [M. Box et al., Nonlinear Optimization Techniques (Olivier & Boyd, London)]. To locate the sources three measurement variables are used: the 3D vectorial active intensity, the normal active intensity, and the quadratic mean pressure. Simulations for three to five emitting sources, aimed at predicting their positions and spectral densities are made. The minimum number of measurement positions that lead to convergence of the algorithm is investigated. The agreement between prediction and reality is good, even when the sources are coherent. In parallel, the impact of the choice of measurement variable on the precision of the results is studied. In the very near field of the source, it is found that identification via 3D intensimetry requires a significantly lower number of measurement positions than does that via normal intensity or quadratic mean pressure.

Speaker independen telephone speech recognition and reference pattern generation.

This paper describes the speaker independent isolated word speech recognition method developed for telephone speech response systems. To recognize speech, input utterances are first frequency analyzed by 19 channel BPFs. The frame cycle used is 8ms. Then the analyzed data undergo logarithmic conversion, normalization of voice chords sound source characteristics by least squares approximation line and time normalization by linear companding to 32 frames. The speech patterns thus obtained undergo pattern matching with multiple reference patterns generated separately for male and female speakers in advance. In applying this recognition method, it is necessary to optimize the reference patterns so that the speech can be correctly recognized in spite of the difference of formant frequencies, the differences in individual speaker's habits, the variations of phonetic positions, non-vocalization, and slight segmentation errors. To evaluate the performance of this recognition method, voices of about 2, 000 persons were recorded through long distance telephone lines. A 16 Japanese words vocabulary was used. A total of 256 male and female reference patterns were generated using the training voice data of about 570 persons. The speech recognition accuracy of this method in recognizing non-training voice data was 97.8 %.