摘要:

A new design strategy for broadbanding ultrasonic transducers was recently presented, which generates a lossless equalizer, matching a resistive source to a piezoelectric transducer with power gain displaying a maximally flat (Butterworth) characteristic. However, three undesirable restrictions are part of the existing algorithm; (i) the center frequency of the design is fixed, limiting its usage to certain passbands, (ii) the design requires the use of an ideal transformer for all source resistance and tranducer combinations but one, and (iii) the resulting element values are often impractical. The purpose of this paper is to present a generalization of the algorithm which broadens its applicability. The main result is an algorithm for the design of a losslesstransformerlessbroadband equalizer with maximally flat power gain, and a delineation of the exact latitude on passbands and source resistances.

ISSN:0001-4966    

DOI:10.1121/1.383687

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

A transmitting hydrophone which remotely senses both absolute pressure and changes in pressure has been developed using a surface acoustic wave (SAW) oscillator. This oscillator is formed by placing a SAW delay line or resonator in the feedback loop of an amplifier. The pressure applied to the hydrophone is converted to a flexural loading of the piezoelectric plate which alters the surface wave velocity on the plate, consequently shifting the oscillator frequency. This frequency modulated signal is easily transmitted to a remote location for signal recovery. The piezoelectric plate thickness and length can be chosen to optimize the sensitivity of the SAW hydrophone. The surface wave element of the oscillator is a planar structure, therefore, it is simple and inexpensive to manufacture. Furthermore, the size and power requirements of the SAW hydrophone are small, typically less than 50 cm3and 300 mW. This paper presents performance data of two SAW hydrophones using SAW oscillators at 44 and 77 MHz in conjunction with a versatile signal demodulation system. Measurements of sensitivity and frequency response were made for both delay line and resonator hydrophones manufactured on lithium niobate andS‐Tquartz substrates, respectively, and compared with measurements obtained from conventional hydrophones in the identical set‐up.

ISSN:0001-4966    

DOI:10.1121/1.383688

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Since compact bone is demonstrably anisotropic and inhomogeneous, the measured quantities yield a plesio‐velocity rather than a true sonic velocity, which makes it difficult to compare velocity measurements among several bone samples. Distribution of the plesio‐velocity for 11 pairs of 2 mm thick specimens from a single mature bovine compact bone sample using 100‐ns well‐damped sonic pulses emitted by a 10‐mHz transducer show that anisotropy exists in both axial and transverse directions and must be associated with the local structure and composition. Changes in the same specimens when wet, dry, and rehydrated show an increase in velocity and anisotropy of the dry over the wet state. The plesio‐velocity is greater in the axial direction, along the bone axis, than in the transverse plane. The change in plesio‐velocity from wet to dry bone is greatest along the bone axis and least in the transverse plane. Changes in dimension, when the bone specimens were dried, show the bone sample to be anisotropic in this parameter also, but in the reverse order from that for the plesio‐velocity. Shrinkage is least along the osteons and a maximum in the transverse plane.

ISSN:0001-4966    

DOI:10.1121/1.383689

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Properties of a vibrating annular membrane are analyzed mathematically and numerically to investigate the relative harmonicity of the higher‐order modes compared with the fundamental mode. The harmonicity depends on the zeros of a cross‐product of Bessel functions. For a ratio of external‐to‐internal diameter up to about 1.2, the higher modes have frequencies which are very nearly exact integer multiples of the fundamental frequency. For circularly symmetric modes, the ratio of all higher radial mode frequencies to exact harmonic values is less than 1.0006 (a logarithmic cent), a ratio imperceptible to a listener. Angle‐dependent modes also give good harmonicity, especially if some lower radial modes are suppressed. Thus the modes of an annular membrane whose external‐to‐internal diameter ratio is less than 1.2 are much more harmonic than those of the full circular membrane of a conventional drum. The theoretical harmonicity is at least as good as reported for stringed melodic instruments (piano, violin). The analysis suggests characteristics for construction of an annular drum‐head which is supported on concentric rims of two cylinders; to sound the drum, a braced hoop might be used to excite radial modes, or strikers with grooved faces might be used to excite angular modes without exciting lower radial modes.

ISSN:0001-4966    

DOI:10.1121/1.383690

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Performance of children aged 9 to 17 years on the SPIN test (Speech Perception in Noise) is described. The 11‐ and 13‐year‐olds performed significantly poorer than 15‐ and 17‐year‐olds, and this difference occurred primarily for high‐predictability sentences presented at a 0‐dB signal‐to‐babble ratio. Performance of nine‐year‐olds was significantly poorer than performance of 11‐year‐olds. Possible reasons for these differences are discussed.

ISSN:0001-4966    

DOI:10.1121/1.383691

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

As part of an investigation of the temporal implementation rules of English, measurements were made of voice‐onset time for initial English stops and the duration of the following voiced vowel in monosyllabic words for New York City speakers. It was found that the VOT of a word‐initial consonant was longer before a voiceless final cluster than before a single nasal, and longer before tense vowels than lax vowels. The vowels were also longer in environments where VOT was longer, but VOT did not maintain a constant ratio with the vowel duration, even for a single place of articulation. VOT was changed by a smaller proportion than the following voiced vowel in both cases. VOT changes associated with the vowel were consistent across place of articulation of the stop. In the final experiment, when vowel tensity and final consonant effects were combined, it was found that the proportion of vowel duration change that carried over to the preceding VOT is different for the two phonetic changes. These results imply that temporal implementation rules simultaneously influence several acoustic intervals including both VOT and the ’’inherent’’ interval corresponding to a segment, either by independent control of the relevant articulatory variables or by some unknown common mechanism.

ISSN:0001-4966    

DOI:10.1121/1.383692

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Recent work at Bell Laboratories has demonstrated the utility of applying sophisticated pattern recognition techniques to obtain a set of speaker‐independent word templates for an isolated word recognition system [Levinsonetal., IEEE Trans. Acoust. Speech Signal Process. ASSP‐27 (2), 134–141 (1979); Rabineretal., IEEE Trans. Acoust. Speech Signal Process.(in press)]. In these studies, it was shown that a careful experimenter could guide the clustering algorithms to choose a small set of templates that were representative of a large number of replications for each word in the vocabulary. Subsequent word recognition tests verified that the templates chosen were indeed representative of a fairly large population of talkers. Given the success of this approach, the next important step is to investigatefullyautomatictechniques for clustering multiple versions of a single word into a set of speaker‐independent word templates. Two such techniques are described in this paper. The first method uses distance data (between replications of a word) to segment the population into stable clusters. The word template is obtained as either the cluster minimax, or as an averaged version of all the elements in the cluster. The second method is a variation of the one described by Rabiner [IEEE Trans. Acoust. Speech Signal Process. ASSP‐26 (3), 34–42 (1978)] in which averaging techniques are directly combined with the nearest neighbor rule to simultaneously define both the word template (i.e., the cluster center) and the elements in the cluster. Experimental data show the first method to be superior to the second method when three or more clusters per word are used in the recognition task.

ISSN:0001-4966    

DOI:10.1121/1.383693

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The present investigation assessed the simultaneous and temporal masking produced by computer‐generated synthetic vowels. The durations (100 and 200 ms) of each of four vowel‐like maskers were employed. The masker was presented at 70 dB SPL. The probe signals were three filtered noise bursts whose spectral distributions corresponded to regions of high spectral energy in three English stop consonants. Quiet and masked thresholds were determined using the method of adjustment. Data are reported for two experienced listeners who participated in all the listening conditions. The results were generally in accord with the results of masking experiments using nonspeech signals in that both the frequency specificity of masking and temporal masking effects were demonstrated.

ISSN:0001-4966    

DOI:10.1121/1.383273

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Simultaneous physiologic measures were obtained on four young adult male subjects as they sustained phonation at seven frequencies within their modal‐to‐falsetto voice range. Data were analyzed using a multiple regression program to determine the contribution of each measure singly and in combination with other measures to the prediction of the resultant voice frequency. Results showed that by far the best predictor was cricothyroid muscle activity for both the pooled data model, and for each individual subject. The contribution of subglottal air pressure and thyroarytenoid muscle activity increased the variance explained by only 4% while the measure of vertical laryngeal position was a significant factor in only one subject’s predictive model. Partial models from the pooled data explained from 67% to 73% of the variance; whereas the obtained measures for individual subjects explained from 90% to 94% of the variance.

ISSN:0001-4966    

DOI:10.1121/1.383694

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

A synthesis method, called speech synthesis from concept, is described which has been designed specifically for providing speech output from information systems. It differs from conventional techniques in that data is passed from the information system to the speech synthesis system, not in the form of text or phonetic transcription, but in the form of an abstract structure called an input concept. The speech synthesis from concept system converts an input concept into speech by using a transformational grammar to generate a well‐formed English sentence and a word concatenation synthesizer to generate the actual speech output. The ’’top down’’ nature of this process reduces the computation required within the information system and enables high‐quality speech to be produced.

ISSN:0001-4966    

DOI:10.1121/1.383695

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP