摘要:

The adaptive filtering technique is one of the major approaches to control the acoustic echoes in teleconferencing systems or hands‐free telephony systems. A brief overview of the performance of different adaptive algorithms for acoustic echo cancellation [cf, S. M. Kuo and H. Zhao, J. Acoust. Soc. Am. Suppl. 186, S56 (1989)] will be presented. A transform domain adaptive filter (TDAF) algorithm is proposed to construct an acoustic echo canceler that has a convergence rate faster than that of the conventional LMS adaptive transversal filter with colored signals. The proposed approach does not introduce extra delay during the process so that it can be used in the application where delay is not allowed. Different orthogonal transforms such as the discrete Fourier transform (DFT), discrete cosine transform (DCT), and discrete Hartley transform (DHT) are used for signals with different eigenvalue spread. Real‐time implementations of this class of canceler with digital signal processors (DSP) will also be discussed.

ISSN:0001-4966    

DOI:10.1121/1.2028115

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Acoustic echo cancellation for teleconferencing or hands‐free telephony constitutes a challenging task for today's digital signal processing techniques. Compared to the well‐established line echo cancellation in telephone networks, the problem takes on a considerably larger size: The impulse response of the echo path to be compensated is longer and may vary more rapidly in time. Moreover, larger bandwidths are often desirable. Therefore, acoustic echo cancellation requires algorithms that adapt far more coeffecients and converge faster than those commonly used in line echo cancelers. On the other hand, direct implementation of sufficiently advanced adaptive filtering algorithms is usually prohibited because of their computational complexity and inherent numerical difficulties. As a way out, the subband approach realizes a “divide and conquer” strategy and promises a reduction of computational complexity and favorable circumstances for fast convergence at the cost of some extra delay. After comparing several possible subband structures, the frequency subband structure is discussed in some detail. For adaptation using LMS‐type algorithms, reasons for the improved convergence behavior compared to a fullband implementation are explained. Design examples are presented to illustrate the effectiveness of the method.

ISSN:0001-4966    

DOI:10.1121/1.2028156

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The spatially selective multimicrophone system, whose principle was first introduced at the 115th ASA meeting, can be easily modified into a directional microphone with range‐dependent sensitivity by appropriately selected distribution of gains of microphone pairs located on a virtual spherical surface. An optimum choice for realizing a super close‐talking microphone with this range‐dependent microphone is investigated by systematic change of gain distribution through computer program, while keeping the spherical boundary shape. The effect of deviation on sensitivity and position of microphone pairs located on the boundary are also analyzed. Furthermore, the simulation study is also extended to the spheroidal shape of the boundary surface and it is made clear that the ratio of major and minor axes up to 2 is allowable without significantly disturbing the spatial characteristics of the multimicrophone system. The experimental results on the first model, occasionally equipped with an analog signal processing part, is also reported.

ISSN:0001-4966    

DOI:10.1121/1.2028206

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

A brief retrospect of how physical oceanography belatedly diffused into underwater acoustics (and vice versa) will be given. It has been known since early MIMI days that acoustic transmissions are characterized by fluctuations of order 1. Early interpretations (under Soviet influence) sought support from Kolomogurov turbulent theories. It has turned out that internal waves are generally the more dominant process. In dealing with mesoscale ocean fluctuations, the internal‐wave‐induced “jitter” is the principal noise limiting the accuracy with which maps of ocean and sound speed (i.e., temperature) can be prepared by tomographic inversion of acoustic travel time.

ISSN:0001-4966    

DOI:10.1121/1.2028252

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Work undertaken at CRPE about gravity waves and turbulence indentification and characterization using acoustic remote sensing is presented. In a first part the techniques of measurement and methods of determination of wayes and turbulence parameters and their representativeness are described. Hence the elements are prepared to discuss, in a second part, observations showing interactions between inertial‐gravity waves and turbulence. In particular, the advantage of acoustic remote sensing to localize critical levels related to gravity waves is demonstrated. The mechanism of wave formation related to wind and reflectivity profiles is also interpreted. Vertically propagating gravity waves and their relationship with entrainment at the level of the inversion layer are also analyzed. As elements of a gravity wave field locally observed are generally studied, rather than the field itself, in the third part, observations of a gravity wave field using a Doppler Sodar network are considered. A discussion is then open about relations between the field characteristics and the local properties of the flow. Adjustment of the wavenumber of the gravity waves field to the “most unstable” wavenumber is discussed, which is important in estimating fluxes and momentum associated with the waves. In the conclusion, the generality of the different observations is considered with special emphasis on the problem of interaction between atmosphere and ocean.

ISSN:0001-4966    

DOI:10.1121/1.2028291

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Two methods have been studied and utilized to statistically characterize short vertical wavelength (high‐mode) internal waves. One technique uses broadband, low‐frequency, simulated pulses transmitted hundreds to thousands of kilometers in conjunction with tomography, the other uses high‐frequency signals transmitted less than a few kilometers. In the first technique, the internal waves cause directional fluctuations of the arriving long‐range rays, which can also be considered as pulse wave front distortions with time and length scales of hours (or less) and hundreds of meters, respectively. Recent frequently sampled, vertical‐array recordings of long‐range pulses enable comparison with theoretical numerically calculated predictions. Understanding the long‐range acoustic fluctuations is required to enable remote monitoring of volumetrically averaged internal waves. In the second technique, unsaturated theory should describe variations in amplitude and phase. Spectra of the short‐range fluctuations can be modeled using ocean sound‐speed spectra, and comparisons to observations are made. The Fresnel length determines the sensitivity in the ocean‐structure wavenumber domain, and adjusting this from tens of meters to a meter or so (a rough limit imposed by absorption) shifts sensitivity from fine structure to microstructure.

ISSN:0001-4966    

DOI:10.1121/1.2028333

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

This paper will present an overview of the relationship between acoustics and arena facilities during the past 20 years. There are three general categories of facilities: small (5000 seats), medium (20 000 seats), and large (50 000 seats). There are two acoustic sources: speech and music. There are many different architectural building and roof types (fabric in tension, air inflated, concrete dome, and wood and steel trusses). There are a number of other interrelated factors that inherently become considerations during the design process leading to the final constructed building. This includes heating, ventilation and air conditioning, score boards/advertising, major uses/home teams, and of course economics. Acoustic consultants have fared well in being able to recognize and implement the necessary design solutions to help attain arena facilities that perform well acoustically and serve the public for sports, cultural arts, and public assembly.

ISSN:0001-4966    

DOI:10.1121/1.2028374

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Multiple‐use requirements for large arenas have grown over the past two decades. Activities now include such diverse events as rodeos, athletic events, tractor pulls, circuses, ice shows, road company musical performances, and large assemblies for speech reinforcement. The multiple use of these facilities places strict requirements on the acoustical design. Speech reinforcement for large assemblies is probably the most exciting, requiring controlled acoustics, low HVAC noise, and high‐quality sound system performance. In order for the facility to work successfully for all activities, all aspects of the acoustical design must be carefully integrated during the design phase. Several large arenas are considered, discussing the acoustical requirements and the acoustical methods used in each. The Marriott Center, a 22 300 seat arena at Brigham Young University is highlighted as an example of a successful large arena with very demanding multiple‐use requirements. The uses and corresponding acoustical requirements are examined in detail, as well as the measures taken to achieve the desired results. These methods are contrasted with less successful methods.

ISSN:0001-4966    

DOI:10.1121/1.2028420

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Just over 2 years ago, in a somewhat unusual move, the Naples/Marco Philharmonic Orchestra decided to build its own concert hall, and the author was engaged to carry out its acoustical and noise control design. The resulting building, which opened officially on 3 November 1989, contains a 1200‐seat hall, a 250‐seat theater, and two 2‐story art galleries, and was built for the unusually low sum of $19 000 000. Although the design for the main hall started out with a considerable bias towards musical performance, the usual demand for an all‐purpose hall arose, leading to the inclusion of a full stage house. The needs of the concert hall were met by the provision of a very flexible orchestra shell. Although the tight schedule left no time for any acoustical adjustments, the hall was a success right from the gala opening performance by its own orchestra, and has received favorable comments from performers varying from Hal Holbrook as Mark Twain to the Canadian Brass and Sir Neville Mariner. The theater is also very flexible and will be used for everything from one‐person shows and chamber music to receptions and banquets.

ISSN:0001-4966    

DOI:10.1121/1.2028463

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The rehabilitation of the Elgin Theater in Toronto, built in 1913, necessitated the installation of an acoustical enhancement system. This led to a study of the various existing systems, most of which involve complex system design, high expense, marginal stability, and sound coloration. This paper develops some simple mathematical techniques for analyzing such systems by examining a few examples. After outlining the advantages and disadvantages of each, it then suggests a new system using time‐variant synthetic reverberation that appears to solve many of the previous problems.

ISSN:0001-4966    

DOI:10.1121/1.2027827

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP