摘要:

Normal and distorted but high‐intelligibility speech forms are compared using a millisecond‐resolution analog ear display. Pattern details which convey intelligibility are identified separately from those which relate to matters of quality. Distorted speech forms include high‐pass filtered normal speech, whispered speech, whistled speech, helium speech, and infinitely clipped speech. The concept of a single principal formant is partly justified. In addition, there exist brief periods when activity penetrates into the ear further than the position of the formant, these events being periodic or random for voiced or whispered sounds, respectively.

ISSN:0001-4966    

DOI:10.1121/1.1976168

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The measurement of transmission loss in the ocean using explosive sources requires knowledge of the spectrum level of the energy released in a given frequency band as it would be measured as in a boundary‐free medium. For the case of shallow charges the measurement of these spectrum levels is often complicated by the fact that the refracted and surface‐reflected arrivals, each containing an initial impulse followed by a series of bubble pulses, cannot be separated by the usual technique of receiver gating. In recent measurements of the spectrum level of 1.8‐lb charges detonated at 60 ft, this difficulty has been obviated by separation of the two arrivals in the frequency domain rather than in the time domain. This was done by smoothing the spectrum of the recorded waveform to reduce the wide variation caused by oscillations of the gas bubble and then adjusting the smoothed spectrum by the amounts necessary to account for the Lloyd's Mirror interaction. The results obtained in this way agree well with values for deeper explosions reported by Christian [E. A. Christian, J. Acoust. Soc. Amer.42, 905–907 (1967)] at the upper end of the spectrum where the levels are nearly depth independent. [Work supported by the U. S. Navy Electronic Systems Command.]

ISSN:0001-4966    

DOI:10.1121/1.1976184

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Mean horizontal velocities of sound propagation in the ocean, defined as the ratio of the horizontal range to the one‐way travel time, have been measured. Single‐dimension RAYDIST equipment is used to measure the horizontal distance between source and receiver, and a radio link is used to determine the one‐way travel time. Measured mean horizontal velocities are compared with values computed by ray‐tracing methods for which the sound‐velocity profile is obtained fromin situbathythermograms. Comparisons of mean horizontal velocities are presented out to ranges of 15 miles for combinations of source and receiver in and below the surface duct.

ISSN:0001-4966    

DOI:10.1121/1.1976198

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Volume backscattering strengths for three depth intervals at the frequencies 2.5–12.5 kHz in13‐octsteps were measured at a number of deep water stations in the Coral Sea in May 1968. At daytime stations the scattering did not vary systematically with depth at the lower frequencies; but at the higher frequencies, the scattering was strongest in the 450‐ to 750‐m depth interval. At evening stations, 1 h before sunset, the scattering was generally a maximum in the interval 0–750 m. At 1 h after sunset, however, the scattering was a maximum in the interval 0–450 m at all frequencies. Over sunset, the average volume scattering strengths at 5, 6, and 8 kHz at a range of 740 m were usually 5 dB greater than the corresponding results at a range of 1500 m. This suggests that the backscattering may have been a function of the horizontal range between the acoustic transducer and the scattering region.

ISSN:0001-4966    

DOI:10.1121/1.1976206

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Closed‐form expressions have been derived for the driving‐point impedance, transfer impedance, and force transmissibility of circular and annular plates with clamped boundaries. The plates are internally damped and are driven either by a sinusoidally varying central point force or by one or more concentric ring forces of variable radii. The circular plates are mass loaded or elastically restrained at their midpoints, or are loaded by an ideally rigid annular mass (rib) of arbitrary radius. Computed results illustrating the frequency dependence of impedance and transmissibility are described, and their physical significance is discussed. Added mass is very effective in increasing plate impedance levels and in blocking force transmission to the plate boundaries, particularly when it is positioned directly beneath the driving force. [Supported jointly by the U. S. Naval Ordnance Systems Command, the U. S. Naval Ship Systems Command, and the U. S. Office of Naval Research.]

ISSN:0001-4966    

DOI:10.1121/1.1976214

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Effective duration and time‐integrated noise level (exposure level) of the sound of a passing vehicle as measured at a point on a sideline, are modified by directionality of the sound source. The factor of proportionality between the effective duration and ratio of slant range to speed is shown to include the integral of the directivity pattern of the source. Since the effective duration increases in proportion to the minimum slant distance and inversely as vehicle speed, the (time‐integrated) noise exposure level is reduced only 3 dB by each doubling of distance and doubling of source speed. Average (rms‐equivalent) sound level, during a period such as an hour, is equal to the total integrated sound level over the hour minus the duration allowance, 10 log (3600 sec/1 sec) = 35.6 dB. Hence, in contrast to maximum noise level that decreases 6 dB with doubling of distance (plus absorption), average noise level from a single moving source decreases only 3 dB for each doubling of distance of closest approach. A routine is described for obtaining the time‐integrated noise level of a single flyover or the average (rms‐equivalent) sound level from a record of sound level versus time for the times that selected levels are exceeded.

ISSN:0001-4966    

DOI:10.1121/1.1975509

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Experimental values of sound absorption were obtained from noise signals recorded at five ground positions during a series of 20 flyovers by two aircraft during a single day of field measurements. Differences in13‐octband noise levels observed at the ground positions for the same angle of radiation from the aircraft were used to determine absorption values which are compared to calculated values of sound absorption based upon both surface and altitude measurements of temperature and humidity. The analysis did not assume uniformity of the sound source from flight to flight nor uniformity of sound power output or directivity characteristics for flights made at different altitudes. Experimental atomspheric absorption values based upon combined data for all flyovers showed good agreement (±0.8 dB per 1000 ft) with calculated absorption values for frequencies from 1250 to 6300 Hz. For the frequency range from 400 to 1000 Hz, experimental values (typically 2 dB per thousand feet) were significantly greater than calculated values. [Work supported by NASA.]

ISSN:0001-4966    

DOI:10.1121/1.1975515

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Lateralization models of the masking‐level difference (MLD) argue that detection under such conditions is of alateralshift in the perceived acoustic image. We examined that assertion by presenting monaural 500‐Hz signals in diotic noise (N0SM) and asking listeners to indicate the lateral position of the resulting auditory image. On randomly chosen trials, we presented a diotic signal in diotic noise (N0S0). Responses to these were assumed to represent perceived “center” and served as the standards against which the responses to N0SM were compared. Signal levels under N0SM and N0S0 were equally detectable as determined in a separate task. Both signals and noise were gated for a duration of 100 msec. As predicted from the model, the lateral scatter under N0SM was sufficient to account for the detection of those signals in an ordinary detection task. We did not find the loss in detection usually associated with gated noise; we attribute this to the fact that subjects had only to lateralize the signal‐plus‐noise, not to compare it to a remembered “center” or to judge the extent of the lateral shift.

ISSN:0001-4966    

DOI:10.1121/1.1975525

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Peripheral transduction may involve the following: (1) the pressure waveform undergoes a first‐derivative transform on the basilar membrane, and (2) the amplitude pattern on the membrane is isomorphically represented by the auditory fiber activity; i.e., the post‐stimulus histogram maintains the shape of the stimulus. Psychoacoustic “centering” experiments should therefore give results consistent with a first‐derivative analysis. Trained subjects listened to pairs of 1000‐Hz low‐pass transients whose members differed in polarity, amplitude, or both. Centering results were in the form of time separations between members of a dichotic pair. With these time separations preserved, stimulus waveforms were later differentiated (giving first‐derivative transforms) and viewed on an oscilloscope and photographed. (These transformed pairs now represented the displacements on the two basilar membranes and the neural patterns that earlier yielded a judgement of center.) Only the rarefaction segments of the waveforms were considered, since these constitute the stimulating phase. When waveform pairs are viewed relative to their rarefactional areas, time separations between members are proportional to area differences, i.e., a form of time‐intensity trade obtains.

ISSN:0001-4966    

DOI:10.1121/1.1975539

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

An analog simulation for the ear responds to complex stimuli with time‐space analog neural patterns having components to several hundred hertz. Photographs of such patterns deriving from the same sound received at spatially separated ears are compared to form a basis for a theory of binaural localization which does not require identical pattern shapes. A different process occurs when the analog ear is equipped with nonlinear mechanisms, ultrasonic echoes then being demodulated to yield complex cochlear patterns whose interpretation provides target quality data and ranging. These two analog mechanisms yield a plausible theory for the functioning of echo‐ranging animals and for binaural localization in man.

ISSN:0001-4966    

DOI:10.1121/1.1975541

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP