摘要:

Because traditional piezoelectric materials have much higher acoustic impedances than water, most hydrophones are ‘‘hard’’ compared to the surrounding water medium. This hardness causes internal and external reflections that manifest themselves as resonance and diffraction effects, respectively. Even nonvoided polyvinylidene fluoride (PVDF), a piezoelectric polymer, has a characteristic acoustic impedance, ρoco, about 2.7 times that of water. With the advent of voided PVDF, however, it is possible to match water’s impedance as closely as desired. Using ρcwindow material and ρcPVDF, we have constructed a ρchydrophone whose response is essentially free of resonance and diffraction effects.

ISSN:0001-4966    

DOI:10.1121/1.394088

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

We present an experimental technique that verifies the theoretical predictions of the resonance scattering theory (RST) which were obtained for fluid‐loaded elastic objects of separable shapes. The rationale in RST permits the separation of the ‘‘backgrounds’’ or rigid‐body portions of the scattering patterns, from the ‘‘resonance’’ portions which are due to the object’s penetrability or elastic composition. For structures of separable shape, this decomposition can be theoretically accomplished for the individual modes, even when these are coupled due to the fluid loading. For general, nonseparable shapes, the decomposition holds for the summed cross sections, rather than for the individual partial waves, since in this case, the modes cannot be individually isolated. In either situation, however, the experimental method described here achieves this crucial RST decomposition of the returns by sampling the pulses scattered by the underwater structure at two temporal locations by means of suitable time‐delay circuitry. One location is within the steady‐state regime of the forced elastic vibration and the other is in the later transient regime of the free vibration (i.e., the ‘‘ringing’’). For the example of solid and hollow elastic cylinders in water, the technique measures the locations of the many modal resonances predicted by the RST in wide spectral bands. It also determines the skewness, amplitude, and the area under each of the resonance shapes. This goes beyond the achievements of any other experimental configuration. The background‐subtracted ‘‘spectrogram’’ thus obtained is the active signature of the object which serves to characterize it uniquely. Once the method has been shown to accurately verify the theoretical RST prediction, in cases where such predictions can be generated, the technique can be used for any complex shape for which predictions may be difficult or impossible to produce. Thus the validity of the RST principles is experimentally confirmed, and an experimental method for active classification of underwater objects was devised and implemented at the place of development of the RST.

ISSN:0001-4966    

DOI:10.1121/1.394089

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The acoustical consequences of articulatory maneuvers of [y] are studied in model experiments in order to obtain insights into articulator programming and speech motor control by elucidating the role of each component maneuver of a speech segment in setting up vocal tract resonance conditions for the spectral features of the speech wave. The maneuvers of [y]are found to provide a maximum and stable plain–flat spectral contrast with [i]. The results can be generalized to different vocal tract sizes. Tongue retraction and larynx depression are rejected as compensations to counteract labial undershoot. Larynx depression is complementary to lip rounding and restores spectral sensitivity to palatal and pharyngeal tongue movements otherwise disturbed by the labial activity. Spectral sensitivity then remains the same for [i]and [y], and there is no need for separate compensation programs for each of these phones.

ISSN:0001-4966    

DOI:10.1121/1.394090

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

An acoustical study of speech production was conducted to determine the manner in which the location of linguistic focus influences intonational attributes of duration and fundamental voice frequency (F0) in matched statements and questions. Speakers orally read sentences that were preceded by aurally presented stimuli designed to elicit either no focus or focus on the first or last noun phrase of the target sentences. Computer‐aided acoustical analysis of word durations showed a localized, large magnitude increase in the duration of the focused word for both statements and questions. Analysis ofF0revealed a more complex pattern of results, with the shape of theF0topline dependent on sentence type and focus location. For sentences with neutral or sentence‐final focus, the difference in theF0topline between questions and statements was evident only on the last key word, where theF0peak of questions was considerably higher than that of statements. For sentences with focus on the first key word, there was no difference in peakF0on the focused item itself, but theF0toplines of questions and statements diverged quite dramatically following the initial word. The statement contour dropped to a lowF0value for the remainder of the sentence, whereas the question remained quite high inF0for all subsequent words. In addition, theF0contour on the focused word was rising in questions and falling in statements, regardless of focus location. The results provide a basis for work on the perception of linguistic focus.

ISSN:0001-4966    

DOI:10.1121/1.394091

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Spectral shape discrimination, or profile analysis, of complex waveforms (21 components) in the presence of broadband noise and special sinusoidal maskers of random amplitude was studied. The first experiment involved the discrimination between a standard flat spectrum and a ‘‘rippled’’ spectrum in broadband noise of different spectrum levels. Thresholds obtained under control conditions, without noise or without a standard, were used to estimate constants of an equation that predict thresholds where standard and noise are both present. The model assumes an external variance, produced by the noise, is added linearly to an internal variance caused by the flat standard. The mean squared error is less than 2 dB. The second experiment involved the detection of an increment on the center component of the 21‐component standard. Added to the standard was an additional masking sinusoid of random amplitude. Both the frequency and the range of the random amplitude were varied and both showed a systematic influence on the detectability of the 1000‐Hz increment.

ISSN:0001-4966    

DOI:10.1121/1.394092

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Canahl [J. Acoust. Soc. Am.50, 471–474 (1971)] measured thresholds for a 1.0‐kHz sinusoid masked either by two or by four surrounding tones. He reported four‐tone masked thresholds that exceeded, by 5–7.5 dB, the energy sum of the masking produced by the individual tone pairs. The present paper reports on a series of experiments investigating the effects of several factors on this 5–7.5 dB ‘‘excess’’ masking. In each experiment, thresholds for a 1.0‐kHz 250‐ms sinusoid were measured as a function of the overall level of two or four equal amplitude sinusoids with frequencies arithmetically centered around 1.0 kHz. For conditions similar to those of the Canahl experiment, 5–6 dB of excess masking was obtained independent of the level of the masking tones. Randomly varying overall level across presentations had no effect on the excess masking. The excess masking was reduced or eliminated when the masking tones were generated using an amplitude modulation technique, when they were gated on and off with the signal, or when their waveshapes were fixed across trials. Canahl’s result may reflect listeners’ ability to detect the signal as a change in the waveshape of the multitone masker.

ISSN:0001-4966    

DOI:10.1121/1.394093

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

A theory is presented that describes the binaural processing of interaural time or phase differences. It is an elaboration of the central spectrum concept for the explanation of dichotic pitch phenomena [F. A. Bilsen, ‘‘Pitch of noise signals: Evidence for a ‘central spectrum’,’’ J. Acoust. Soc. Am.61, 150–161 (1977)]. The generation is postulated for central activity patterns (CAP) due to binaural interaction. From these CAPs the central processor selects specific spectral information that constitutes the information for lateralization, dichotic pitch, binaural masking, etc. Here, a strategy is assumed to be based on central spectra (CS) rather than on interaural cross correlation. For the calculation of the central activity patterns a number of assumptions have been introduced. The peripheral filters are supposed to be infinitesimally narrow. The analog filter outputs from corresponding filters at both ears are thought to interact by means of a linear delay‐and‐add mechanism. The squared output (power) of such a binaural (addition) network constitutes the CAP. The theory has been tested with lateralization and BMLD measurements using dichotic stimulus configurations characteristic of the perception of dichotic pitch. The predictions of the model concerning the pitch and the lateralization of the pitch images as well as the BMLD patterns for this kind of stimuli are confirmed.

ISSN:0001-4966    

DOI:10.1121/1.394039

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Recently, Klein and Hartmann [J. Acoust. Soc. Am.70, 51–61 (1981)] investigated a new dichotic pitch, called the binaural edge pitch (BEP). They used computer‐generated periodic noise signals to generate BEP. In the study presented here, the BEP is investigated in order to evaluate the predictions of the central spectrum theory with regard to this stimulus. Pitch‐matching experiments using a nonperiodic BEP stimulus, produced by means of a modulation technique, led to the conclusion that the strongest pitch sensation in the BEP has the character of a weak fluctuating pure tones in noise, which corresponds to a frequency, equal or almost equal to the frequency of the phase transition. This result fits in with the predictions of the central spectrum theory, which, for instance, does not need the assumption of central lateral inhibition for explaining this pitch. Furthermore, it is shown that this theory can also predict the results obtained in lateralization measurements and BMLD measurements using BEP stimuli as well as related stimuli. The results are compared with the data obtained by Klein and Hartmann.

ISSN:0001-4966    

DOI:10.1121/1.394040

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Conventional and restricted‐listening psychophysical tuning curve paradigms were used to evaluate (1) the masking ability of forward maskers of different envelope characteristics, and (2) the relationship between off‐frequency listening effects and the envelope characteristics of both the variable masker and stationary masker used to restrict listening to a narrow region surrounding the probe. Maskers were selected so as to differ widely in the degree of fluctuation in their envelopes. The masker with the largest amplitude fluctuations exhibited greater forward‐masking ability than other stimuli; this effect was observed on the high‐frequency branch and within the tip region of the tuning curve. It is suggested that differences in masking ability may reflect the use of different signal detection cues. The results are also consistent with previous reports [D. Johnson‐Davies and R. D. Patterson, J. Acoust. Soc. Am.65, 756–770 (1979); B. J. O’Loughlin and B. C. J. Moore, J. Acoust. Soc. Am.69, 1119–1125 (1981a)] which suggest that off‐frequency listening is a factor contributing to the sharpness of psychophysical tuning curves. This effect is largely dependent, however, on the envelope characteristics of both variable and stationary maskers.

ISSN:0001-4966    

DOI:10.1121/1.394465

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Studies of persons with conductive hearing loss have revealed substantial degradations in binaural hearing abilities. Described here is a model based on the hypothesis that this degradation is due to high levels of bone‐conducted signals relative to air‐conducted signals. The model makes quantitative predictions for the effects of conductive impairment on measurements of interaural discrimination. Qualitative predictions for binaural advantages in detection and speech intelligibility are also made by employing auxiliary models. Generally, available data are consistent with the models, although strong tests have not yet been performed.

ISSN:0001-4966    

DOI:10.1121/1.394041

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP