摘要:

The scanning acoustic microprobe is a novel system which probes and characterizes, from a limited acoustic window, the fine‐scale structural features of an object, point‐by‐point, using a multiplicity of acoustic pulses all aimed and focused at that point. Spherically symmetric, three‐dimensional Gaussian pulses are synthesized to measure the backscatter diffraction pattern of the least‐resolvable volume of scatterers centered at the point in question. The size and distribution of the scattering volume is forced to be constant, independent of frequency and angle. This method is analytically simple, compared with other pulse‐echo techniques, and is applicable to scatterers ranging continuously in size from Rayleigh scatterers to specular reflectors. This is the first of a number of papers describing the development and application of systems based on these concepts. The analytical principles will be described herein for examination of one point at a time. In a companion paper appearing in this issue [F. E. Barber, J. Acoust. Soc. Am. ▪▪, ▪▪▪–▪▪▪ (1991)], application to measurement and characterization of a discrete, flat, circular ‘‘piston’’ will be presented. Application to human tissue imaging and tissue characterization will be described in a subsequent third paper. The primary features detected experimentally are the strength of nondirective patterns, and the strength, orientation, and directivity of angle‐dependent echo functions associated with planar or layered structures. Fine‐scale structural features of a scattering center are obtained either by pattern recognition ink(data) space or inverse Fourier transformation. It is shown that when the bandwidth criteria are met to produce a spherically symmetric point spread function, scattering phenomena are completely described by only two parameters, namely the center frequency of the pulse‐echo system and the characteristic diameter of the Gaussian point spread function.

ISSN:0001-4966    

DOI:10.1121/1.401288

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

In a pulsed ultrasound beam, echoes detected from a flat, circular piston of arbitrary size depend on the time‐space characteristics of the entire pulse‐echo measurement system, being a function of as many parameters as it takes to accurately define the system. In the limiting case of a target that is small relative to the spatial extent of an interrogating plane wave, an echo pattern is known to be a relatively simple function of the dimensionless productk0b, wherek0is the wave number andbis the radius of the target. In a companion paper preceding this one [F. E. Barber, J. Acoust. Soc. Am.90, 8–17 (1991)], the author has described the scanning acoustic microprobe, a pulse‐echo system in which the time‐space properties of the interrogating waves are specified completely byk0and a single additional parameters0, which is the characteristic radius of a spherically symmetric, Gaussian‐distributed scattering volume. In this system, the reflection pattern of a flat, circular piston of any arbitrary size is thus a function of two dimensionless parameters, namelyk0bandb/s0. In this paper, this functional relationship is derived, a physical system is described, and analytical and experimental results are reported. It is shown that the diameter, orientation, and impedance mismatch properties of this simple target can be measured unambiguously over a range of target sizes from about a wavelength (2π/k0) to a beam diameter (about 3s0). For a typical ultrasound system, this is about a 5–1 range; i.e., a range extending to target sizes about five times smaller than can be detected in a simpleB‐mode imaging system. Theoretical and experimental results are described and discussed in detail. The implications of such a system for quantitative analysis of more complex target structures and constituents are explored. The methods lead naturally to a new technique for imaging that will display fine‐scale features not seen by any other method.

ISSN:0001-4966    

DOI:10.1121/1.401305

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Three arguments are presented to demonstrate the distinction between energy propagation and wave‐front propagation in an acoustic field where the reactive intensity is nonzero. This distinction is especially useful for understanding the acoustic near field. Physical interpretations of the active and reactive intensity vectors and their contributions to the energy propagation described by the instantaneous intensity are summarized. Also, two differential equations are developed that show the interdependence of the active and reactive intensity vectors. Other important results show the contribution of the reactive intensity to the wave fronts propagating at speeds other than the speed of sound, and also show that energy associated with the reactive intensity does propagate to the far field.

ISSN:0001-4966    

DOI:10.1121/1.401290

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

A procedure for designing quantitative echo sounders, whose main purpose is fisheries resource surveys, is described. The quantitative echo sounder must be designed under the specific criteria, such as minimum error, taking into account the purpose, external conditions, and several acoustic characteristics. The acoustic characteristics needed in the design procedure, for example, the scattering properties of fish, are reviewed briefly. In the main part, the method to determine the pulse width, bandwidth, operating frequency, transducer diameter, and gain allocation for each stage of the receiver is described. A convenient ‘‘universal diagram’’ is introduced for determining the basic parameters. The diagram serves also for users of sounders. Application of the method to two kinds of sounders is demonstrated. The optimum frequency for quantitative echo sounders is discussed and the frequency of 38 kHz, being used worldwide, is shown to be a reasonable frequency.

ISSN:0001-4966    

DOI:10.1121/1.401297

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Echo sounding is a powerful and widely used technique for remote sensing of the marine environment. In order to enhance the power of the echo sounder, a postprocessing system has been designed and realized in standard software that is essentially machine independent. This has been done by adhering to the following international standards: UNIX operating system, C programming language, X Window Systems, Structured‐Query Language (SQL) for communication with a relational database, and Transport Control Protocol/Internet Protocol (TCP/IP). Preprocessed data are transferred from the echo sounder to the postprocessing system by means of a local‐area network (LAN), namely Ethernet. Development of the postprocessing system, for analysis of such diverse scatterers as plankton, pelagic, and bottom fish, and the bottom itself, is documented in the following way. The history of echo integration is summarized. User requirements for the new system are listed. Reasons are given for the choice of the particular computing environment, including both hardware, software, and external communications. The system design, consisting of data flow and graphical user interfaces, is described. Implementation of the system is defined through integration techniques and a discussion of performance issues. Operating procedures and the first field trials of the system are described. Several features characteristic of and perhaps unique to the postprocessing system are, for example: (1) user definition of arbitrarily shaped integration regions, including non‐constant‐depth intervals, by means of interactive graphics; (2) preprocessor error correction, e.g., adjustment of the noise threshold or redefinition of the detected bottom; (3) use of several color map techniques in order to extract such information as signal strength and shape; and (4) the scheme of interconnections of graphical user interfaces, database, and data files. This work does not introduce a set of computer instructions. It does describe a design philosophy and method of realization that may have broader applications in acoustics than that ostensibly concerned only with the quantitative estimation of fish abundance.

ISSN:0001-4966    

DOI:10.1121/1.401261

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Sonar transducers are usually calibrated prior to installation on a ship. They are not, however, recalibrated after installation even though their receiving (and transmitting) properties can change significantly. This report presents a procedure for theinsitucalibration of sonar transducers at any desired time after installation when the ship is in open water. The procedure provides an up‐to‐date knowledge of the complex free‐field sensitivity (or response) of each of the array transducers. This knowledge can be used to minimize, perhaps even eliminate, the adverse effects on array performance due to changes in the properties of one or more transducers. Theinsitucalibration procedure is based on a form of three‐transducer reciprocity calibration that uses sound propagation factors to account for the influence of the ship’s structure. The report describes how to obtain numerical values for the required sound propagation factors. It also describes how to use two‐transducer comparison calibration to simplify theinsitucalibration process, at least for highly reliable sonars.

ISSN:0001-4966    

DOI:10.1121/1.401275

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

In order to determine in which medium, air or tissue, harbor porpoise (Phocoenaphocoena) sounds are produced, the air in the nasal cavities was substituted with heliox (80% helium and 20% oxygen), and the effect on click frequency spectrum was studied. The sound speed is 1.86 times higher in heliox than in air and the resonance frequency of a fixed cavity filled with heliox is increased by this factor as compared to that of the same cavity filled with air. The harbor porpoise emits click sounds restricted in the frequency domain to two relatively narrow bands, one around 2 kHz and one in the 120‐ to 140‐kHz range. The results show that the stronger high‐frequency component was not at all affected by the heliox, suggesting that it was produced and shaped in some tissue structure(s), and not in gas. The low‐frequency component obviously was affected by the heliox, although the frequency rise did not match the expected theoretical factor. This was probably due to simultaneous, uncontrolled changes in cavity volume, interfering with the heliox effect. It is concluded, however, that the low‐frequency component was a gas bound phenomenon, taking place in the nasal pathways. The results also show that the stronger high‐frequency component always occurred together with and in the beginning of the low‐frequency component, indicating that both were the result of the same production event. These results are in line with previous observations of air bound click sounds being heard when porpoises phonated with open blowhole, and of simultaneous vibrations occurring in the upper nasal passways, in the tissues containing the right dorsal bursae.

ISSN:0001-4966    

DOI:10.1121/1.401281

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

The relationship between final hammer velocity and maximum amplitude of radiated piano sound was investigated. Piano tones with varying hammer velocities were produced by a computer‐monitored acoustic piano containing optical sensors and solenoids, and the sounded tones were recorded and digitized for analysis. Maximum amplitudes over the duration of the sounded tones were linearly proportional to piano hammer velocities for a range of frequencies and hammer velocities. Changes in room acoustics did not alter the linear relationship. Measurements of maximum amplitudes of individual tones and combined tones (dyads) also indicated a linear relationship between the sum of the maximum amplitudes of the individual tones and the maximum amplitude of the dyads. These findings indicate that the principle of superposition holds for peak amplitudes of sounded piano tones. Findings are discussed with regard to production and perception of musical dynamics.

ISSN:0001-4966    

DOI:10.1121/1.401249

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Two methods are described for speaker normalizing vowel spectral features: one is a multivariable linear transformation of the features and the other is a polynomial warping of the frequency scale. Both normalization algorithms minimize the mean‐square error between the transformed data of each speaker and vowel target values obtained from a ‘‘typical speaker.’’ These normalization techniques were evaluated both for formants and a form of cepstral coefficients (DCTCs) as spectral parameters, for both static and dynamic features, and with and without fundamental frequency (F0) as an additional feature. The normalizations were tested with a series of automatic classification experiments for vowels. For all conditions, automatic vowel classification rates increased for speaker‐normalized data compared to rates obtained for nonnormalized parameters. Typical classification rates for vowel test data for nonnormalized and normalized features respectively are as follows: static formants—69%/79%; formant trajectories—76%/84%; static DCTCs 75%/84%; DCTC trajectories—84%/91%. The linear transformation methods increased the classification rates slightly more than the polynomial frequency warping. The addition ofF0 improved the automatic recognition results for nonnormalized vowel spectral features as much as 5.8%. However, the addition ofF0 to speaker‐normalized spectral features resulted in much smaller increases in automatic recognition rates.

ISSN:0001-4966    

DOI:10.1121/1.402350

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

The goal of cross‐language voice conversion is to preserve the speech characteristics of one speaker when that speaker’s speech is translated and used to synthesize speech in another language. In this paper, two preliminary studies, i.e., a statistical analysis of spectrum differences in different languages and the first attempt at a cross‐language voice conversion, are reported. Speech uttered by a bilingual speaker is analyzed to examine spectrum difference between English and Japanese. Experimental results are (1) the codebook size for mixed speech from English and Japanese should be almost twice the codebook size of either English or Japanese; (2) although many code vectors occurred in both English and Japanese, some have a tendency to predominate in one language or the other; (3) code vectors that predominantly occurred in English are contained in the phonemes /r/, /æ/, /f/, /š/, and code vectors that predominantly occurred in Japanese are contained in /i/, /u/, /N/; and (4) judged from listening tests, listeners cannot reliably indicate the distinction between English speech decoded by a Japanese codebook and English speech decoded by an English codebook. A voice conversion algorithm based on codebook mapping was applied to cross‐language voice conversion, and its performance was somewhat less effective than for voice conversion in the same language.

ISSN:0001-4966    

DOI:10.1121/1.402284

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP