Journal of the Acoustical Society of America

Foamed aluminum is a promising candidate in hydroacoustics as a possible pressure-release material. Previously, the measurement of its dynamic shear modulus has been reported for various densities and pore sizes of the material, [Proc. IEEE, 1985 Ultrasonics Symp. 2, 1052–1055 (1985)]. In an attempt to complete the characterization of the material, its Young’s modulus and Poisson’s ratio were measured by means of laser Doppler vibrometry. The lowest value for the ρc product found was 0.20 SI Mrayl, about 15% of the ρc product of water. Some of the samples appear to be anisotropic. An attempt was made to measure the five compliance coefficients of one foamed-aluminum type that follow from assuming uniaxial symmetry. The results did not conform to the relationships pertinent to this type of symmetry.

This paper deals with measurements carried out with pulsive signals to determine the spectral region associated with dominant pitch perception. The stimulus consisted of the sum of (1) a low-frequency band of a unipolar pulse train with fundamental frequency f0 (or f0+Δf) and upper cutoff frequency fe and (2) a high-frequency band of a unipolar pulse train with fundamental frequency f0+Δf (or f0) and lower cutoff frequency fe. In the experiments f0 was 100, 200, and 400 Hz, respectively; Δf/f0 was either 3% or 6%; and over-all sensation level was between 30 and 50 dB. When the fundamental frequencies were interchanged, a pitch change “up” or “down” was heard, depending on the “crossover” frequency fe. For fe larger than the sixth harmonic, the low-frequency band always dominated the pitch percept. Changing the sensation level of the low-frequency band with respect to the higher-frequency band, the minimum sensation level for dominant pitch perception was determined. It was found that, for a given fe, the low band tended to dominate the pitch perception as long as its amplitude exceeded a minimum absolute level. Dominance was found to be independent of Δf. By selectively limiting the number of components in the low-frequency band, the spectral region dominant for the perception of pitch was determined more precisely. This spectral region covered the frequency band consisting of the third, fourth, and fifth harmonics for signals with fundamental frequencies in the range of 100–400 Hz.

Three single-scattering approximations for coefficients in Biot’s equations of poroelasticity are considered: the average T-matrix approximation (ATA), the coherent potential approximation (CPA), and the differential effective medium (DEM). The scattering coefficients used here are exact results obtained previously for scattering from a spherical inclusion of one Biot material imbedded in another otherwise homogeneous Biot material. The CPA has been shown previously to guarantee that, if the coefficients for the scattering materials satisfy Gassmann’s equation, then the effective coefficients for the composite medium satisfy Brown and Korringa’s generalization of Gassmann’s equation. A collection of similar results is obtained here showing that the coefficients derived from ATA, CPA, or DEM all satisfy the required conditions for consistency. It is also shown that Gassmann’s equation will result from any of these single-scattering approximations if the collection of scatterers includes only spheres of fluid and of a single type of elastic solid.

Studies evaluating phonological contrast learning typically investigate either the predictiveness of specific pretraining aptitude measures or the efficacy of different instructional paradigms. However, little research considers how these factors interact—whether different students learn better from different types of instruction—and what the psychological basis for any interaction might be. The present study demonstrates that successfully learning a foreign-language phonological contrast for pitch depends on an interaction between individual differences in perceptual abilities and the design of the training paradigm. Training from stimuli with high acoustic-phonetic variability is generally thought to improve learning; however, we found high-variability training enhanced learning only for individuals with strong perceptual abilities. Learners with weaker perceptual abilities were actually impaired by high-variability training relative to a low-variability condition. A second experiment assessing variations on the high-variability training design determined that the property of this learning environment most detrimental to perceptually weak learners is the amount of trial-by-trial variability. Learners’ perceptual limitations can thus override the benefits of high-variability training where trial-by-trial variability in other irrelevant acoustic-phonetic features obfuscates access to the target feature. These results demonstrate the importance of considering individual differences in pretraining aptitudes when evaluating the efficacy of any speech training paradigm.

The perceptual consequences of trial-to-trial changes in the voice of the talker on spoken word recognition were examined. The results from a series of experiments using perceptual identification and naming tasks demonstrated that perceptual performance decreases when the voice of the talker changes from trial to trial compared to performance when the voice on each trial remains the same. In addition, the effects of talker variability on word recognition appeared to be more robust and less dependent on task than the effects of word frequency and lexical structure. Possible hypotheses regarding the nature of the processes giving rise to these effects are discussed, with particular attention to the idea that the processing of information about the talker’s voice is intimately related to early perceptual processes that extract acoustic–phonetic information from the speech signal.

The present work reviews theories and empirical findings, including results from two new experiments, that bear on the perception of English vowels, with an emphasis on the comparison of data analytic ‘‘machine recognition’’ approaches with results from speech perception experiments. Two major sources of variability (viz., speaker differences and consonantal context effects) are addressed from the classical perspective of overlap between vowel categories in F1×F2 space. Various approaches to the reduction of this overlap are evaluated. Two types of speaker normalization are considered. ‘‘Intrinsic’’ methods based on relationships among the steady-state properties (F0, F1, F2, and F3) within individual vowel tokens are contrasted with ‘‘extrinsic’’ methods, involving the relationships among the formant frequencies of the entire vowel system of a single speaker. Evidence from a new experiment supports Ainsworth’s (1975) conclusion [W. Ainsworth, Auditory Analysis and Perception of Speech (Academic, London, 1975)] that both types of information have a role to play in perception. The effects of consonantal context on formant overlap are also considered. A new experiment is presented that extends Lindblom and Studdert-Kennedy’s (1967) finding [B. Lindblom and M. Studdert-Kennedy, J. Acoust. Soc. Am. 43, 840–843)] of perceptual effects of consonantal context on vowel perception to /dVd/ and /bVb/ contexts. Finally, the role of vowel-inherent dynamic properties, including duration and diphthongization, is briefly reviewed. All of the above factors are shown to have reliable influences on vowel perception, although the relative weight of such effects and the circumstances that alter these weights remain far from clear. It is suggested that the design of more complex perceptual experiments, together with the development of quantitative pattern recognition models of human vowel perception, will be necessary to resolve these issues.

The purpose of this study was to replicate and extend the classic study of vowel acoustics by Peterson and Barney (PB) [J. Acoust. Soc. Am. 24, 175–184 (1952)]. Recordings were made of 45 men, 48 women, and 46 children producing the vowels /i,i,e,ε,æ,a,open‘‘oh’’,o,u,u,Λ,hook backward‘‘eh’’/ in h–V–d syllables. Formant contours for F1–F4 were measured from LPC spectra using a custom interactive editing tool. For comparison with the PB data, formant patterns were sampled at a time that was judged by visual inspection to be maximally steady. Analysis of the formant data shows numerous differences between the present data and those of PB, both in terms of average frequencies of F1 and F2, and the degree of overlap among adjacent vowels. As with the original study, listening tests showed that the signals were nearly always identified as the vowel intended by the talker. Discriminant analysis showed that the vowels were more poorly separated than the PB data based on a static sample of the formant pattern. However, the vowels can be separated with a high degree of accuracy if duration and spectral change information is included.