摘要:

The physical theory of diffraction is applied to acoustical diffraction problems, using the concept of elementary edge waves scattered in the vicinity of an infinitesimal edge element. Far from the edge element, these elementary edge waves are described by the circular function of complex arguments. Various definitions of elementary edge waves are discussed. The theory is formulated in general form, namely for the scattering surfaces with arbitrary sharp edges. Faces of edges are assumed to be acoustically soft or hard and the edges themselves are assumed to be smoothly curved (in terms of wavelength). An angle between faces varies slowly along the edge. This theory enables one to calculate the dominant term in the high‐frequency asymptotic expansion for primary and multiple edge waves. Asymptotics of this kind are found for the scattered field in the ray region, near a smooth caustic, on the shadow boundary, and along a focal line. The connection between the physical theory of diffraction and other asymptotic methods is established.

ISSN:0001-4966    

DOI:10.1121/1.398226

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

The input impedance at primary bronchi of excised human lungs was measured in the frequency range from 2–5000 Hz. For the measurements, a self‐developed acoustic impedance head and a narrow‐band measuring system with sinusoidal excitation were used. The lungs were inflated and deflated by using an arrangement called respiratory state controller. The impedances were thus measured at different states of lung inflation. An already existing mathematical model was developed further to cover not only fairly inflated lungs, but also deflated ones. The parameter sensitivity of this model is investigated. The acoustomechanical parameters of the model were fitted to match the impedances measured. It turns out that some of these parameters are hardly calculable. The values given in this paper were chosen to agree with the measurements and to be physically reasonable. Although the measurements were performed at primary bronchi, the model is able to predict also impedances at the top end of the trachea (at different respiratory states). This impedance is useful for speech signal processing applications. The model prediction of the trachea impedances agrees well with previous results of other authors.

ISSN:0001-4966    

DOI:10.1121/1.398227

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

The implications of a fractal model of medium structure for the angular dependence of the ultrasonic differential scattering cross section and for the frequency dependence of the total ultrasonic scattering cross section are explored. The results for the differential scattering cross section agree well with published experimental values for liver and those for the total scattering cross section are not inconsistent with the literature data.

ISSN:0001-4966    

DOI:10.1121/1.398228

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

In an echolocation experiment, the target detection performance of a beluga and a bottlenose dolphin were similar, but each produced different patterns of echolocation click trains. The beluga emitted three different patterns of echolocation clicks. A pattern I click train started with low‐amplitude clicks, followed by packets of clicks. A packet contained several clicks with interclick intervals less than the two‐way travel time to the target; the interpacket intervals were greater than the two‐way travel time. A pattern II click train consisted of a combination of individual clicks, some with intervals less than and some greater than the two‐way travel time. This pattern did not contain packets. The third pattern of click trains consisted of individual clicks with interclick intervals less than the two‐way travel time. However, the bottlenose dolphin always emitted clicks with interclick intervals greater than the two‐way travel time. These differences in click patterns suggest that the beluga has a different echolocation strategy than the bottlenose dolphin.

ISSN:0001-4966    

DOI:10.1121/1.398229

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

A method is described that allows measurement of the bowing parameters in violin playing under normal conditions. The measured parameters include bow position, bow velocity, bow–bridge distance, and bow force. The use of the method is illustrated by registrations of typical bowing patterns (sustained notes, scales,crescendo–diminuendo,sforzando, andsaltellato). The examples are analyzed with a focus on the players’ use of the bow–bridge distance and bow velocity in controlling the dynamic level. The correspondence between predicted and observed changes in the dynamic level is discussed, as well as the safety margins in bow force. The measurement method is a development of equipment earlier described [A. Askenfelt, J. Acoust. Soc. Am.80. 1007–1015 (1986)].

ISSN:0001-4966    

DOI:10.1121/1.398230

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

The four lowest formant frequencies were measured in eight members of the bass section of a good amateur choir under two conditions: (1) when reading the text of a poem aloud; and (2) when performing the same text as a song. Certain formant frequency differences were observed that were similar to those previously found between professional singers’ spoken and sung vowels. In singing, the intersubject scatter of the three lowest formant frequencies was smaller, and the fourth formant was lower.

ISSN:0001-4966    

DOI:10.1121/1.398231

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

A system for simple quasiarticulatory speech synthesis is described. It is based on an articulatory model, which is controlled by seven parameters. The synthesizer employs a stylized vocal tract model that is realized using wave digital filter techniques. It includes a self‐oscillating glottis model, voiceless excitation in the tract, damping, a nasal tract, and a radiation load that allows the simulation of lip protrusion. The synthesizer runs in real time on a signal processor. The described model was fit to natural speech using a Kalman filter algorithm. Simple rules for the synthesis of unrestricted German speech are described.

ISSN:0001-4966    

DOI:10.1121/1.398232

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

In this paper, a method is developed to employ vowel duration properties in a hidden Markov model (HMM)‐based large vocabulary speaker trained recognition system. It is found that each of the vowel phonemes spoken in isolated words can be divided into three allophones, each corresponding to a largely distinctive range of vowel durations. Such a division is based upon the phonetic context where the vowel occurs. In order to incorporate the durational information, each vowel’s HMM is trained using a maximum‐likelihood method with three separate sets of transition probabilities, corresponding to the three allophones. The output distributions of the HMM are assumed to be the same for all three allophones and trained jointly, to make best use of the limited number of available training tokens. The duration‐specific HMMs for vowel allophones have been evaluated in isolated word recognition experiments for two male speakers. The results show that the performance of the recognizer is improved, reducing the error rate by approximately 14% compared with recognition results without the use of the vowel durational models. The performance improvement resulting from use of the vowel durational models is due to reduction of postvocalic consonant errors arising from their contextual correlation with vowels of different durations, as well as to improved discrimination between vowel phonemes.

ISSN:0001-4966    

DOI:10.1121/1.398233

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

A series of perceptual experiments was conducted to investigate the perceptual cues for place of articulation for the voiced pharyngeal /// and the voiced uvular /3/ consonants in Arabic. Synthetic consonant–vowel stimuli, in which the vowel was the long vowel /aa/ of Arabic, were used in the experiments. In the first experiment, stimulus continua were constructed by systematically varying the trajectories of the first and second formant frequencies (F1 andF2) independently between the values appropriate for the two consonants. In the second experiment, the bandwidth ofF2 for the pharyngeal stimuli and the bandwidth ofF1 for the uvular stimuli were manipulated. Results of the first experiment show that the onset value ofF1(F1o) is essential in discriminating between the two consonants, while that ofF2 is not. Results of the second experiment show that widening the bandwidth ofF1 increases the percent of uvular responses and enhances the naturalness of the uvular stimuli, whereas it decreases substantially the number of pharyngeal responses. Increasing the bandwidth ofF2 had no effect on either the percent identification of the pharyngeal or the naturalness of the synthetic stimuli.

ISSN:0001-4966    

DOI:10.1121/1.398234

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP

摘要:

Abilities to detect and discriminate ten synthetic steady‐state English vowels were compared in Old World monkeys (Cercopithecus,Macaca) and humans using standard animal psychophysical procedures and positive‐reinforcement operant conditioning techniques. Monkeys’ detection thresholds were close to humans’ for the front vowels /i–I–q–1–W/, but 10–20 dB higher for the back vowels /v–a–c–U–u/. Subjects were subsequently presented with groups of vowels to discriminate. All monkeys experienced difficulty with spectrally similar pairs such as /v–a/, /q–1/, and /U–u/, but macaques were superior to Cercopithecus monkeys. Humans discriminated all vowels at 100% correct levels, but their increased response latencies reflected spectral similarity and correlated with higher error rates by monkeys. Varying the intensity level of the vowel stimuli had little effect on either monkey or human discrimination, except at the lowest levels tested. These qualitative similarities in monkey and human vowel discrimination suggest that some monkey species may provide useful models of human vowel processing at the sensory level.

ISSN:0001-4966    

DOI:10.1121/1.398235

出版商:Acoustical Society of America    

年代:1989

数据来源: AIP