摘要:

This work gives the nonlinear solution for the response of isotropic cylindrical shells to transient acoustic loading. The approach is numerical and in particular applies the USA‐STAGS code which combines the finite element method for the structure with the Doubly Asymptotic Approximation (DAA) for the fluid. We assess the influence of both large strain and plasticity on the response of the structure and the fluid. One important finding is that the modal responses are dependent upon the loading intensity, a situation not observed for the linear case.

ISSN:0001-4966    

DOI:10.1121/1.2018056

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Adaptive transform coding (ATC) has recently been proposed as a technique for good quality, robust coding of speech at bit rates from 9.6 to 16 kb/s. In this paper we report on two new developments: (1) the use of a homomorphic vocoder model for the “side‐information” channel in ATC and (2) the application of these techniques to a real‐time implementation of ATC on an array processing computer. In the ATC coder speech is buffered into blocks and transformed into a frequency domain representation. The transform coefficients are then quantized for transmission. The discrete cosine transform (DCT) is generally used because it minimizes “end effects” in the blocks. The step sizes and number of bits in the quantizers are adaptively controlled to track the dynamic spectral variations of speech. The control of the step sizes and bit assignment is based on a local estimate of the spectrum which is parameterized, encoded, and transmitted as “side‐information” to the receiver. In previous work an LPC vocoder model was used to efficiently model the spectrum in order to take advantage of known properties of speech. In this paper we investigate the use of a homomorphic vocoder model which accomplishes essentially the same thing. The properties of the “pseudo‐cepstrum” in the homomorphic model (which is based on a DCT analysis) are explored in order to define the side information needed to characterize the DCT spectrum. It is also shown that the choice of the homomorphic model leads to a particularly convenient form of the ATC algorithm for a real‐time block processing implementation on an array processing computer. Also it is shown that the log spectrum output of the homomorphic model is in a convenient form for both the bit assignment algorithm (which now becomes a straightforward quantization operation) and the quantization of the transform coefficients (which is done in the log domain). Details of the algorithm will be discussed and examples of real‐time coded speech will be played. Good quality is achieved at 9.6 kb/s and nearly transparent quality is achieved at 16 kb/s.

ISSN:0001-4966    

DOI:10.1121/1.2018059

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

An algorithm for adaptive differential pulse‐code modulation (ADPCM) has been implemented in real time on a Bell Laboratories produced digital signal processing integrated circuit [J. S. Thompson and J. R. Boddie, IEEE ASSP Conference, Denver (April 1980)]. The algorithm demonstrates the flexibility and programability of the IC processor for doing medium‐scale signal processing. The processor can decode an instruction, fetch data, and perform a 16‐bit by 20‐bit multiplication and a full 36‐bit product accumulation in one machine cycle of 800 ns. An 8‐kHz, 4‐bit, ADPCM coder and decoder have been implemented for simultaneous operation, consuming approximately one‐half of the processor's capability. General details of the IC architecture and the adaptation of the ADPCM algorithm to this architecture will be discussed.

ISSN:0001-4966    

DOI:10.1121/1.2018062

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A multi‐level segmentation of a one‐dimensional signal may be induced by hierarchical ordering of subsets in a corresponding parameter space. This concept has been introduced to design a segmentation algorithm that creates a special three‐level segmentation for the speech signal. For preclassification it uses the parameters short time prediction gain and short time variance to form the second level of a segment hierarchy containing the classes “pause,” “fricative,” “vocal,” and “nasal oriented.” By merging the segment classes “pause” and “fricative” as well as “vocal” and “nasal oriented” the first level is formed. Since the vocal parts comprise more than 50% of speech, a clustering procedure has been added to create a third level containing four classes that roughly correspond to four different vowel classes. The parameter vector for the clustering algorithm is the sampled LPC‐generated log power spectrum together with theL2distance. Five samples of speech, with a duration of 1 min each, have been processed. The resulting segmentation served as a basis for a number of segment length statistics which suggest applications in speaker verification and speech coding. [Work supported by VW Foundation, at the University of Hannover, Germany.]

ISSN:0001-4966    

DOI:10.1121/1.2018067

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Automated directory listing retrieval has been a goal of the Bell System for a long time. An early form of such a system, based on the use of spoken spelled names, was a speaker trained system and it used a simplified directory search algorithm. Subsequent improvements and modifications to both the recognition algorithm and the directory search procedure have led to the current implementation in which the overall system is speaker independent and can automatically find the name in the directory which provides the best acoustic match to the spoken name. The new system can automatically detect and correct simple (i.e., single letter) anomalies in the spelling of the name, including letter substitutions, inversions, deletions, and insertions. If a conflict in the detected name occurs (e.g., two or more names with the same or close acoustic distance scores), the system automatically requests additional information to help resolve the ambiguity. In evaluational tests on an 18 000 name Bell Laboratories directory, the directory listing retrieval system found the unique correct name in 98.3% of the trials, on average, even though the acoustic recognizer provided the correct letters only about 70% of the time.

ISSN:0001-4966    

DOI:10.1121/1.2018072

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Although societies of technical professions are not chartered to provide studies for certified credit (in the sense of educational institutions), each society has addressed the matter of education in its respective field. Such concerns are manifested in various forms: society‐sponsored workshops, seminars, special sessions, topical conferences, and even selected certification of individual technical qualifications. Additional society contributions include directories of accredited course offerings by educational institutions within selected fields of special concern and information on job opportunities and advanced degree graduates produced by educational institutions within selected subfields of specialization. Thus, even though professional societies do not offer accredited courses of study, they tend to be an active partner in education‐related functions. During the past decade, noise‐related studies have received increased attention by both educational and professional institutions, resulting in a marked upturn of events relating to educational activities by professional societies. Specific education‐related activities by professional societies have been selected for abbreviated description of the important role they play in the total educational process in the field of noise control.

ISSN:0001-4966    

DOI:10.1121/1.2018075

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Earlier papers in this special session have considered the needs of the user of the end product of the process. This paper describes how users can influence the educational process by means of two written examinations administered by the Institute of Noise Control Engineering (INCE/USA). The INCE Fundamentals Examination is a two‐hour, closed‐book, multiple‐choice examination covering the fundamentals of acoustics and noise control engineering. The INCE Professional Examination is divided into two parts, each of four hours duration. The first part, Principles of Noise Control Engineering, covers fundamental concepts including the application of basic acoustics, mechanical dynamics and properties of the ear to noise control problems. The second part, Practice of Noise Control Engineering, requires a selection of problems from a number of individual specialities, including instrumentation and measurements, hearing conservation, noise problems in buildings, in the community, and in several specific industries. A concerted effort has been made to develop questions that are typical of those encountered by the practicing engineer. Hence, the exam questions are of a practical, rather than academic nature. By adjusting the educational process to meet the requirements of the INCE examination program, industries' needs are matched.

ISSN:0001-4966    

DOI:10.1121/1.2018080

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

AT‐matrix code suitable for acoustic scattering has been developed and used to study the resonances present in water droplets in air, whenever they scatter incident sound energy. The numerical determination of the resonance portions of the back‐scattering amplitudes is compared to exact analytical expressions suited to this case [J. George, J. Acoust. Soc. Am (in press)], and excellent agreement is found. Several resonances (i.e., fundamental and overtones) present in several of the initial modes have been computed and displayed for various combination of substances inside and outside the droplet. The analysis is useful in the resonance study of sound scattering by aerosols and fogs. [H. Überall is also at Catholic University, Washington, DC 20064 and was additionally supported by Code 421 of ONR.]

ISSN:0001-4966    

DOI:10.1121/1.2018086

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The optoacoustic effect, through which absorption of chopped optical energy results in the production of sound at the chopping frequency, has become an important analytical tool during the past decade. High‐power lasers, operated at visible and infrared wavelengths, have made possible the generation of measurable acoustic signals through optical absorption by a variety of gases as well as by aerosols and solid materials. Device optimization has been attempted by a number of researchers. Elements of the problem are discussed here in the context of a system intended for the measurement of concentrations of nitrogen dioxide as low as 1 part in l09. Of concern are the use of an acoustically resonant gas cell, reduction of extraneous sound generated where the chopped laser beam passes through cell windows, and enhancement of signal relative to acoustic and electronic noise.

ISSN:0001-4966    

DOI:10.1121/1.2018087

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Previous research in which listeners matched a pure tone to the perceived pitch of tape recorded whispered vowel stimuli has suggested that the perceived pitch corresponds closely with the second formant frequency [Thomas, J. Acoust. Soc. Am.46,468–470 (1969); McGlone and Manning, Folia phoniat.31,9–14 (1979)]. We investigated the pitches of computer generated whispered vowels /i, u, a, Λ/. Five listeners were asked to match the pitch of an adjustable rippled noise stimulus to the perceived pitch of the whispered vowels. Rippled noise was selected as the matching stimulus because it is spectrally similar to whispered vowels, thus minimizing the well known problems involved in pitch matching pure tones to complex stimuli. Results indicate that the perceived pitch does not correspond with the second formant frequency. These findings will be discussed in light of current theories of pitch perception. [Work supported by NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2018097

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP