摘要:

A numerical scheme for generating both the trapped mode and continuum portions of acoustic fields for a horizontally stratified ocean and bottom is presented. The technique is based on the fact that the branch line integral corresponding to the continuum portion of the field can be performed by Hankel transforming a modified Green's function. The modified Green's function is obtained by removing the pole contributions from the actual Green's function. The continuum portion is then added to the trapped mode portion to form the total synthetic field. The technique has the advantage that it is fast, accurate, and can be used for a more general geoacoustic model than the Pekeris waveguide. Synthetic results for several examples are presented and discussed.

ISSN:0001-4966    

DOI:10.1121/1.2021704

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Detectability of a 100‐ms 1000‐Hz sinusoid was measured in quiet and in broadband noise having a spectral level of 20 dB SPL. Intensity discrimination of an in‐phase increment was studied for standards that were −9, −6, −3, 0, 3, 6, 9, 12, and 18 dB relative to threshold. When discrimination thresholds were plotted in terms of signal amplitude versus standard level, all subjects showed nonmonotonic functions (negative masking). Smallest thresholds occurred when the standard was just detectable. These discrimination thresholds were about 10 dB lower than detection thresholds. Psychometric functions were measured for simple detection (no standard) and for intensity discrimination with a standard at threshold. For intensity discrimination,d′ was proportional to signal amplitude. For simple detection,d′ was proportional to signal amplitude to the fourth power. The results in noise agreed well with those in quiet, although there was a tendency to obtain more “negative masking” in quiet and psychometric functions for detection were slightly steeper in quiet. [Work supported by NSF.]

ISSN:0001-4966    

DOI:10.1121/1.2021712

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Early results on synthetic‐vowel formant amplitude discrimination by Flanagan [J. Acoust. Soc. Am.27,1223–1225 (1955); J. Speech Hear. Disord.22,205–212 (1957)] indicated that ΔIfor overall vowel level was about ± 1.5 dB, but that ΔIforF2 was about ± 4 dB. The latter result was forF2 ≃ − 12dBre: F1 for the “comparison” vowel. Subjects made a same‐different judgment which may have affected the interpretation of these results. Here we report ΔIfor several “comparison” vowels which differ in amplitude relations amongF1,F2, andF3. In addition, we report on perception of extreme shifts in formant amplitude, Implications for computer recognition of speech will be discussed.

ISSN:0001-4966    

DOI:10.1121/1.2021714

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Experimenters have frequently noted large individual differences in listeners' abilities to discriminate auditory patterns differing only in the frequency of one pattern component. Whereas some subjects require weeks of practice with large pattern differences, others can make fine discriminations almost immediately. To further characterize such subject‐dependent differences in performance, we investigated pattern discrimination by listeners with only minimal paychoacoustic experience. Since most naive listeners can detect a frequency change if the target component is much longer than the other pattern components, we measured the target tone duration required for correct discrimination 71% of the time in a standard/2AFC procedure, for five levels of target frequency difference (Δ ∫) ranging from 18 to 92 Hz. Nine of the ten pattern components were 45 ms in duration, while the target tone duration varied according to an adaptive track. The target tone (920 Hz) was always the second pattern component. The nine other tones, with frequencies between 500 and 1500 Hz, were randomly ordered on every trial. Threshold durations were estimated from adaptive tracks for each Δ ∫. Generally longer target tone durations were required to discriminate small Δ ∫'s than for larger frequency differences, paralleling the effects of duration on frequency discrimination of brief tones in isolation. Each listener clearly fell into one of two nonoverlapping groups: those with high duration thresholds for all Δ ∫'s tested, and those who consistently required much shorter target tone durations.

ISSN:0001-4966    

DOI:10.1121/1.2021720

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Using LPC analysis, an investigation of anticipatory vowel coarticulation was made of 100‐ms segments of Arabic voiceless fricatives (/h, x, ∫, and s/) spoken in isolation and in three prevocalic contexts (/ɑ, i, and u/) by three native speakers. The degree of coarticulation for each prevocalic fricative segment was determined by assessing both the amount of spectral change from the isolated production, and the relationship of prevocalic fricative peaks to vowel formats. Strong coarticulation was observed for all speakers in all three vowel contexts for the pharyngeal fricative /h/, while minimal coarticulatory effects were present for the dental fricative /s/. Vowel specific trends were evident for the palatal /∫/ and velar /x/ fricatives: strong coarticulation was seen for /xi/, /xu/, /∫i/ and/ ∫ɑ/ and not the remaining utterances. Individual differences were evident with respect to degree of coarticulation. The three speakers behaved similarly for only three of the 12 fricative‐vowel utterances. Results are discussed in terms of the articulatory compatibility principle. Present address: Biosciences Lab., 3M Center, St. Paul, MN.

ISSN:0001-4966    

DOI:10.1121/1.2021724

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The contrast between “He showed her the bird seed,” and “He showed her bird the seed,” can be marked by an article and prosody, or by prosody alone. Aural comprehension of such sentences develops between ages 5 and 13, and comprehension of sentences marked by prosody alone is last to emerge [R. J. Scholes, D.C. Tanis, and A. Turner, Lang. Speech19,212–223 (1976)]. We have replicated this finding among a population of 8‐ and 10‐year‐old children, and, in three subsequent experiments, have explored the basis of age‐related changes in use of prosody. The first experiment reveals that age‐related differences in use of prosodic cues extend to another syntactic structure. The second shows that young children's perception of the relevant prosodic cues is superior to their syntactic interpretation of them. The third shows that while emphasis of prosodic cues does not improve comprehension, disruption of either work stress or juncture pause can penalize children's performance, more so for older children than younger ones. Thus it may not be the perception of word stress or juncture pause so much as the syntactic interpretation of them that increases between ages 8 and 10. A further finding is that interpretation of prosodic cues is related to reading ability. Relative to the good readers at each age, the poorer readers possessed equivalent perceptual skills, but their sentence comprehension skills were less mature. [Work supported by Bryn Mawr College, NICHD, and BRS.]

ISSN:0001-4966    

DOI:10.1121/1.2021728

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Global characteristics of fundamental frequency (F0) contours in English were examined in three task environments, including (a) spontaneous speaking about an academic topic, compared with subsequent oral reading of a transcript thereof, (b) oral description of pictures, and (c) oral reading of isolated sentences whose focus was determined by variations in preceding questions. The results of the first two studies showed in general absence ofF0declination in spontaneous speech, in agreement with other recent work. The results of the third study indicated thatF0declination occurs throughout the oral reading of isolated sentences, even when sentence focus is located near the end of the sentence, in disagreement with preliminary data for Swedish [G. Bruce, Lund Univ. Working Papers22,51–116 (1982)]. These and additional results are discussed in terms of a model ofF0patterns that sharply distinguishes global and local attributes. [Work supported by NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2021734

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

At short ranges the phenomena relevant to the propagation of motor vehicle noise include inverse square law, interference between direct and ground reflected waves, the finite impedance of the ground, refraction, and turbulence. The interference between direct and reflected waves is a rapidly varying function of receiver distance and height from the source. If the ground has a detectable finite acoustic impedance a shadow region is produced which is penetrated at low frequencies by a ground wave. For ground having impedance discontinuities a diffracted wave originates at the interface. Strong wind and temperature gradients close to the ground produce a refractive shadow that is penetrated by a creeping wave. Wind and temperature fluctuations (turbulence) cause sound energy to be redirected by scattering and enhance sound pressure levels in the vicinity of acoustic shadow regions. In addition to the sound propagation phenomena, mechanisms associated with the moving vehicle cause variability in motor vehicle noise measurements. Experiments designed to separate the causes of this variability are discussed. The source of variability for moving vehicles can be either refraction in the turbulent wake of a moving vehicle or possibly the complicated diffraction pattern around a vehicle that changes rapidly with frequency.

ISSN:0001-4966    

DOI:10.1121/1.2021738

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Existing standard tests of motor vehicle noise, such as passby tests, are based on sound pressure measurements with single fixed‐location microphones. Recent developments in two‐microphone acoustic‐intensity techniques, and in instrumentation, permit the practical measurement of the sound power of vehicles and of components, such as engines. This can be performed in a normal test environment; a special acoustical facility such as an anechoic chamber or a reverberation room is not required. Sound power, which is a single‐number measure of the total output of a noise source, appears better suited to determining the overall effect of a vehicle on community noise. Also sound power is usually measured indoors, thereby avoiding scheduling delays due to bad weather and the inherent variability in the data associated with outdoor testing. Good repeatability (i.e., a standard deviation less than 5% or 0.2 dB) has been demonstrated in the measurement of the sound power of a medium‐duty truck, using acoustic intensity methods in an indoor test. Similar repeatability has been demonstrated in the measurement of the sound power of an engine for a heavy‐duty truck. These and other advantages and disadvantages of the use of acoustic intensity measurement methods for standard tests are discussed in the presentation.

ISSN:0001-4966    

DOI:10.1121/1.2021740

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

A problem that is basic to our understanding of the structural acoustics of submerged structures is that of a point or line driven fluid‐loaded elastic plate. It has caught the attention of a number of investigators over the last two decades. The farfield radiation properties of such plates is well understood. The nearfield, because of its analytical intractibility, has been more elusive. This presentation reviews and presents some recent numerical evaluations of the plate transfer admittances and nearfield pressure patterns. Characteristic features of the admittance are dependent on the ratio of the drive frequency to the coincidence frequency. Below coincidence, the response consists of a fluid‐modified flexural wave and a spatially decaying acoustic component. Above coincidence, fluid loading introduces a radiation loss component into the response. The nearfield pressures below coincidence show evidence of an interference pattern between the acoustic wave launched at the drive point and the exponentially decaying pressure field generated by the modified flexural wave. Isobar pressure contours for the case of a flexural wave scattered by a structural discontinuity will also be shown.

ISSN:0001-4966    

DOI:10.1121/1.2021747

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP