摘要:

A new approach to transducer design is introduced in which a transducer is viewed as a continuum of infinitesimal, locally reacting elements. The transducer response is the coherent sum of the responses of the infinitesimal elements. Hence variations in transducer response characteristics will be produced by variations in the relative contribution of each element. It is thus possible to produce designed transducer characteristics through selection of a suitable local sensitivity shading function. This new approach is used to design a foil electret acoustic antenna which achieves with a single transducer direction characteristics similar to these of a linear microphone array. Five methods for accomplishing sensitivity variation in the electret microphone have been identified: variation of active width, variation of charge density, variation of actual airgap, variation of foil thickness, and variation of effective airgap. It is shown that compared to a linear microphone array, the single transducer acoustic antenna offers advantages of lower sensitivity to small construction errors, directional behavior over a wider frequency range, easier construction, and potentially higher signal to noise ratio.

ISSN:0001-4966    

DOI:10.1121/1.391607

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Previous reports from our laboratory indicate that ultrasonic backscatter from myocardium exhibits a cyclic variation during the cardiac cycle that is reduced sharply by ischemia, a process which impairs both systolic contraction and diastolic relaxation. These results suggest that the cyclic variation of backscatter may be related to the cyclic variation of the contractile performance of the myocardium. Because contractile performance of the left ventricle is known to exhibit regional variability, the present study was undertaken to determine whether such regional differences in contractile performance are paralleled by differences in the magnitude of the cyclic variation of ultrasonic backscatter. Measurements obtained from representative zones of three regions of the hearts of ten open‐chest dogs indicate that the magnitude of the cyclic pattern of variation of backscatter parallels the regional differences in contractile performance throughout the left ventricle with the maximum variation (5.5±0.9 dB peak‐to‐peak amplitude) occurring at the apex, intermediate values (4.3±0.8 dB) at the midwall, and minimum (0.5±1.0 dB) at the base. These results suggest that the ultrasonic backscatter may be sensitive to the regional myocardial contractile performance.

ISSN:0001-4966    

DOI:10.1121/1.391608

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Electropalatographic and acoustical data on vowel‐to‐vowel (V‐to‐V) coarticulatory effects were obtained for Catalan VCV sequences, with the consonants representing different degrees of tongue‐dorsum contact (dorsopalatal approximant [j], alveolo‐palatal nasal [ν], alveolo‐palatal lateral [Y], and alveolar nasal [n]). Results show that the degree of V‐to‐V coarticulation in linguopalatal fronting andF2 frequency varies monotonically and inversely with the degree of tongue‐dorsum contact, carryover effects being larger than anticipatory effects. The temporal extent of coarticulation also varies with the degree of tongue‐dorsum contact, much more so for anticipatory effects than for carryover effects. Overall, results indicate that V‐to‐V coarticulation in VCV sequences is dependent on the mechanical constraints imposed on the tongue dorsum to achieve dorsopalatal closure during the production of the intervening consonant. Moreover, anticipatory effects, but not carryover effects, involve articulatory preprogramming.

ISSN:0001-4966    

DOI:10.1121/1.391609

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Speech is normally heard against a background of other sounds, yet our ability to isolate perceptually the speech of a particular talker is poorly understood. The experiments reported here illustrate two different ways in which a listener may decide whether a tone at a harmonic of a vowel’s fundamental forms part of the vowel. First, a tone that starts or stops at a different time from a vowel is less likely to be heard as part of that vowel than if it is simultaneous with it; moreover, this effect occurs regardless of whether the tone has been added to a normal vowel, or to a vowel that has already been reduced in energy at the tone’s frequency. Second, energy added simultaneously with a vowel, at a harmonic frequency near to the vowel’s first formant, may or may not be fully incorporated into the vowel percept, depending on its relation to the first formant: When the additional tone is just below the vowel’s first formant frequency, it is less likely to be incorporated than energy that is added at a frequency just above the first formant. Both experiments show that formants may only be estimated after properties of the sound wave have been grouped into different apparent sound sources. The first result illustrates a general auditory mechanism for performing perceptual grouping, while the second result illustrates a mechanism that may use a more specific constraint on vocal‐tract transfer functions.

ISSN:0001-4966    

DOI:10.1121/1.391610

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Objective evaluation of normal and hoarse voices is performed considering the characteristic that hoarse voices show a prominent fundamental frequency intensity compared with harmonics in the voice spectrum. The relative harmonic intensityHr, obtained from a stable portion of the sustained vowel /a/, is defined as the intensity of the second and higher harmonics expressed as a percentage of the total voice intensity. Ninety‐five percent of the normal voices examined haveHrlarger than the critical value of 67.2%, whereas 90% of the hoarse voices haveHrsmaller than the critical value. The harmonic‐intensity analysis thus provides good discrimination between normal and hoarse voices.

ISSN:0001-4966    

DOI:10.1121/1.391611

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Three selective adaptation experiments were conducted to investigate whether intervocalic stops are perceived as the end of the preceding syllable or as the beginning of the following one. The pattern of adaptation effects (and just as importantly, noneffects) indicated that intervocalic stop consonants are perceptually more like syllable‐initial than syllable‐final ones. From this it might be concluded that the perceptual system breaks down a vowel–consonant–vowel (VCV) utterance into a V–CV sequence. However, the similarity of an intervocalic stop to a syllable‐initial one is quite limited; the consonant in a VCV is apparently treated as essentially different from consonants in either VC or CV utterances. These results clarify, and perhaps complicate, the role of the syllable in models of the speech perception process.

ISSN:0001-4966    

DOI:10.1121/1.391612

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Understanding how the durations of acoustic segments vary in natural language can lead to more intelligible synthetic speech, and to improved automatic recognition. Toward this goal, a 111‐word French paragraph was read by 29 native speakers from France. Measured durations of acoustic segments were significantly shorter than those in earlier studies of stressed words in French sentences read from a list. Previously recognized trends (short schwa vowels and function words; long unvoiced fricatives, nasalized vowels, and prepausal syllables) are confirmed and quantitative results are given. Vowels were longer preceding voiced fricatives (but not prior to /r/), and were also longer at sentence‐internal pauses than at the end of a sentence. Standard deviations of acoustic segment durations (at fixed positions in the paragraph) across speakers averaged less than 25% in most cases. The exceptional, larger deviations occurred primarily in segments adjacent to pauses. Speaking rate variations could account for only one‐sixth of the deviations, the rest being attributable to relatively free variation across speakers. A generative model of French durations, suitable for synthesis‐by‐rule, is presented, and applications to automatic recognition are discussed.

ISSN:0001-4966    

DOI:10.1121/1.391613

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

This study investigates the role of intonation for the intelligibility of deaf speech. The intonation contours of Dutch sentences spoken by deaf children were manipulated using digital signal processing techniques, including LPC analysis. Sentence intonation was corrected by replacing the originalF0 contour of the deaf utterance with an artificial contour derived from a formalized intonation grammar. Three types of intonation corrections were produced, differing with respect to the underlying accent structure and the type ofF0 movements used. The overall results show that intonation correction yields a small but significant improvement in intelligibility of 7% (from 20% to 27% words correctly identified). The largest gain is obtained after removal of over‐accentuations. To evaluate the interaction with temporal aspects, intonation corrections were also implemented on temporally corrected sentences. Total growth in intelligibility due to these combined corrections amounts to 13%. Thus it is concluded that no dramatic gain in intelligibility may be expected if speech pathologists succeed in teaching their deaf pupils to have better control over the suprasegmental aspects of their speech.

ISSN:0001-4966    

DOI:10.1121/1.391614

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

A fundamental question in the perception of melody is how listeners use pitch information to arrive at a sense of musical scale. We investigated possible ways in which this might be achieved. Listeners were required to detect notes incompatible with scalar structure in the course of melodic sequences. Within the parameters of our experimental sequences, the results showed that detection of nonscalar notes could be based on identifying nonscalar interval combinations (e.g., F♯, A, Bb), as well as by matching successive notes to a developing scalar schema. The strength of the scalar schema was influenced by relations between notes in the circle of fifths, with notes closer together in the circle of fifths (e.g., C, G, D, A) leading to a stronger schema than notes further apart (e.g., C, G, E, B).

ISSN:0001-4966    

DOI:10.1121/1.391615

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Auditory discrimination abilities of professional musicians were compared with those of nonmusicians. The stimuli for the frequency‐discrimination tasks were 300‐msecsinusoidal tones, 300‐msec square waves, and tone patterns consisting of ten 40‐msec tones played sequentially. The musicians’ difference thresholds for single tones were betweenΔf /f=0.001 and 0.0045. One‐half of the nonmusicians attained thresholds almost as low; the rest attained larger thresholds, up toΔf /f=0.017. The results for the pattern stimuli show a clearer separation between the nonmusicians and musicians, whose median differencethresholds were about three times smaller. However, nonmusician listeners who had previously trained with patterns not in the test set had different thresholds,substantially smaller than those obtained by the musicians. The appropriateness of preferential recruitment of musicians for psychoacoustic research is discussed. The responses to amusical background survey and correlations between the survey items and discrimination performance are contained in a supplement to this paper [PAPS JASMA76, xxx‐xx].

ISSN:0001-4966    

DOI:10.1121/1.391605

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP