摘要:

Some possible attentional aspects of post‐stimulus signal processing were investigated in a modified masked‐signal detection paradigm. The signal was a 1000‐Hz sinusoidal waveform 20 msec in duration and sated at positive zero‐crossing of the waveform. The signal was masked by a broad‐band (360–3360 Hz) Gaussian noise. The effect of a decrease in the amplitude of the masking noise, when confined to a limited frequency range, was investigated in terms of both the frequency range of the change and the temporal relationship between the offset of the signal observation interval and the onset of the decrease. An immediate decrease in masking noise in frequency regions outside the critical band of the signal decreased detectability.

ISSN:0001-4966    

DOI:10.1121/1.1982682

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

A low‐pass noise (1500‐Hz cutoff) with a sinusoidal variation in its amplitude spectrum (ripple noise) was used to mask a 1000‐Hz signal (10 msec) in both a forward and a simultaneous masking procedure. The masked thresholds of the signal were measured as a function of the number of peaks (ripples) in the amplitude spectrum of the noise. The procedure was similar to that used by Houtgast who reported it at the 83rd meeting of the Acoustical Society. Houtgast used a pulsation threshold technique with ripple noise to study frequency selectivity. Pulsation threshold is similar to simultaneous forward and backward masking. The data of the present study indicate that results similar, but not identical, to Houtgast's can be obtained with forward masking alone. The frequency selectivity obtained with the forward masking procedure is sharper than has been previously obtained and might indicate the presence of lateral inhibition.

ISSN:0001-4966    

DOI:10.1121/1.1982685

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Voiceless fricatives in American English were studied from readings of a continuous text. The wide range of duration (30 msec to more than 200 msec) is explainable in terms of phonological conditions. For example, a fricative in the stressed‐syllable initial position is about 20% longer than in the same phoneme sequence in unstressed position; single fricatives are longer than those in clusters with the same stress and positional conditions; a fricative preceded by a nasal is about 30% shorter than one under equivalent conditions with a nonnasal. Overall intensity of fricatives is not simply proportional to duration, but rather depends on stress and boundary conditions. Fricatives in prepausal position are longest but weakest. For a given phonological condition (e.g., word‐initial stressed, and single), overall intensity reflects the sentence stress. There are consistent relationships between fricative intensity and spectral distribution. Recently we have argued that the stop consonants vary systematically to mark, among other things, word boundaries and the beginnings of stressed syllables. This study shows that allophonic variations of the fricatives carry the same information.

ISSN:0001-4966    

DOI:10.1121/1.1982692

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Recent timing control research has shown that when a smaller linguistic segment within a repeated utterance is produced either shorter or longer than its average duration, the resulting deviation constitutes a timing error that is temporally compensated by the remaining segments in the utterance. In the present study, timing errors and the extent to which they are compensated define different levels of temporal interaction. Temporal interactions were studied within a phrase spoken in isolation and within the same phrase spoken in a sentence context. The data, presented as significant negative Pearson correlations (p<0.05) between various adjacent segment durations, support several tentative conclusions on the timing control of repeated utterances: (1) different‐sized utterances have different levels of temporal interaction; (2) temporal interaction effects extend across phoneme, syllable, word, and phrase boundaries; (3) there appears to be no basic unit of timing for English utterances, but a hierarchy of units ranging in size from a CV or VC syllable to a sentence; and (4) identical durational errors may be compensated for by a variety of adjacent segment lengths.

ISSN:0001-4966    

DOI:10.1121/1.1982696

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Trained male singers sang (chest and falsetto registers) and spoke CVCV syllables embedded in a carrier phrase, using as stressed‐unstressed/unstressed‐stressed paradigm. The consonant /t/ was employed throughout in combination with the vowels /i‐a‐u/. All syllables were segmented into three acoustic elements: (1) silent interval, (2) noise burst, and (3) phonation. The silent intervalplusthe noise element were considered to correspond with the consonant, and the phonation segment with the vowel. In appropriate instances, measures were made of duration, amplitude, fundamental frequency, and formant characteristics of the segments from spectrographic records. Relations among segments are reported as a function of modes of utterance and stress. Inferences are drawn concerning possible differential articulatory and phonatory demands on the production system as a consequence of syllabic stress during singing and speech.

ISSN:0001-4966    

DOI:10.1121/1.1982703

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

A new, general definition is given for the critical angle of reflection in anisotropic materials. While the critical angle for reflection at a liquid‐isotropic‐solid interface can be written in the formsinθc = vI/vR, we show here that, in general, for an anisotropic solid, the right‐hand side of this expression must be modified by the factor cosφ/cosβ, where φ is the angle between the normal to the refracted wave in the solid and its energy flux vector and β is the angle between the energy flux vector and the component of the refracted wave normal on the interface. Numerical calculations have been made for this general definition for a water‐quartz interface for planes of incidence about thezaxis (thexyDiane being the interface). These calculations are compared with the value of the critical angle as determined by the unmodified definition. It is shown that this earlier definition can lead to large errors when one uses the experimental technique of measuring the critical angle to evaluate the elastic constants of the solid.

ISSN:0001-4966    

DOI:10.1121/1.1982708

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Parametric acoustic array performance has been demonstrated with several different transducers. Three‐inch‐diameter transducers with primary frequencies between 250 and 300 kHz have produced good parametric acoustic beams at 10, 20, and 40 kHz difference frequencies with nearly constant beamwidth across this frequency band. A parametric acoustic array operating at 20‐kHz difference frequency was compared to a 100‐kHz conventional transducer for bottom profiling capability in Lake Washington. Echograms were obtained demonstrating the capability of the lower frequency beam to produce subbottom, as well as bottom returns.

ISSN:0001-4966    

DOI:10.1121/1.1982713

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The parametric difference frequency radiator appears to offer advantages over conventional sources used for hydrophone calibration, i.e., wide bandwidth with a single transducer, narrow beamwidths, and short pulselengths. The combination of these characteristics promises simplification of calibration procedures and elimination or reduction of boundary reflection problems. Experiments are described which measure the performance of the parametric source for calibration purposes and which point out some of the special problems inherent in this new technique.

ISSN:0001-4966    

DOI:10.1121/1.1982718

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

A theory is developed for axial flow fans which predicts the harmonic and broad‐band acoustic radiation from the stator due to interaction with rotor viscous wakes. Both the harmonic and broad‐band spectrum components are calculated from a unified model using methodology from the theory of random pulse modulation. The stator is modeled as a circular array of pulsed dipoles. The amplitude and arrival time of each pulse are random variables whose means correspond to the values calculated for harmonic rotor‐stator interaction theory. The standard deviations of these random variables are measures of the turbulence level in the blade wakes. For the model proposed, the solution is exact and the results are instructive: when pulse amplitude modulation (PAM) is imposed on a periodic stator source, new broad‐band energy is generated whose spectrum shape is similar to the envelope of harmonics at high frequencies. The harmonic radiation is unchanged. When pulse position modulation (PPM) occurs, new broad‐band energy is radiated but at the expense of harmonic energy. The theoretical results are discussed with reference to directivity patterns and radiation efficiency, and the harmonic component is compared with the previous Lowson and Embleton/Theissen analyses. The transfer of harmonic to random energy through PPM is discussed. At frequencies significantly above duct cutoff, it is shown for a fixed stator solidity that the spectrum is essentially independent of the number of stator vanes. In order to show the capabilities of this new theory, calculations are compared in detail with experimental data and modulation levels are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1982727

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Definitive experimental knowledge of discrete‐frequency noise reduction, which can be obtained in an aircraft turbofan engine through increased axial spacing between the fan rotor and outlet guide vanes, has been lacking. An experimental scale‐model research program has been undertaken to fill this void. Using a unique heavy‐gas scale‐model anechoic test facility, rearward radiated discrete frequency and broad‐band noise was investigated for a scale model fan. Data has been obtained for fan tip Mach numbers of 0.7–1.4, and rotor to OGV spacings of 0.13, 0.5, 1.0, and 2.0 rotor chords. Discrete frequency noise reductions up to 17 dB were obtained. At close spacing, discrete frequency reduction was at a rate greater than 6 dB per double spacing. Relative harmonic content was not influenced by spacing and reduction was independent of rotor speed. No significant change in broad‐band noise was observed.

ISSN:0001-4966    

DOI:10.1121/1.1982728

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP