摘要:

Previous attempts at synthesizing voiced fricatives have failed to yield acceptably natural‐sounding segments. One possible reason for this failure is that the synthesis models have been global, whereas some important characteristics of these segments may reside in their period‐by‐period structure. Our goal in this study was therefore to compare the auditory quality of digitally manipulated /v, ð, z, and ȝ/ segments, in various V‐V contexts. High‐quality tokens were digitized at 24 kHz, and individual pitch periods were marked by hand using interactive software. Comparison stimuli were then created via the following manipulations: (1) reordering of alternate periods; (2) reordering triples of periods; (3) replacement of all odd‐ (even‐) numbered periods by their even‐ (odd‐) numbered neighbors; (4) similar replacements modulo 3; (5) random reordering of periods. Furthermore, these manipulations were sometimes restricted to the onset, steady state, or offset portions of the segments. These digitally spliced segments were then presented to listeners for discrimination, naturalness, and likeness judgments. Results of these comparisons and their implications for synthesis of natural‐sounding voiced fricatives will be discussed.

ISSN:0001-4966    

DOI:10.1121/1.2022172

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

This paper will describe a newly developed expert system which uses linguistic knowledge to align the phonetic content of two different words or phrases and score their similarity. The development of the system arose out of a need to have an automatic scoring algorithm for intelligibility testing for text‐to‐speech systems and other synthetic‐speech coding and recognition systems. The system uses an automatic text‐to‐phone algorithm to translate the input and reference ASCII text strings to phonemic units, aligns them using linguistic knowledge‐based decision criteria and a dynamic programming optimization, and outputs the aligned strings as well as tabulating the phoneme confusions.

ISSN:0001-4966    

DOI:10.1121/1.2022180

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

No experimental data have been published to date on the air/water/air acoustic waveguide with flat, sloped, or rough boundaries. In the conventional air/water/solid acoustic waveguide, the presence of the solid introduces the Scholte mode. The solid surface roughness causes not only energy leakage from the water waveguide to the solid, but it causes spreading of the energy over a wide time window. In order to study the normal modes interference and coupling phenomena in a rough waveguide, the problem would be greatly simplified if we could eliminate the Scholte mode and the energy leakage to the solid. A novel experimental technique is described which uses a thin stretched rubber membrane covered with a water layer from above. Controlled pressurized air below the membrane is used to counteract the weight of the water layer and obtain a flat surface at the bottom of the water waveguide. The water layer has a free top surface and a free bottom surface. Ultrasonic broadband pulses are propagated in the air‐suspended water waveguide. Theoretical and experimental results are compared for the free flat parallel boundaries waveguide ease. Scattering objects are placed on the surface of the membrane to form a rough or periodic boundary. Experimental findings are presented providing physical insights into the shallow‐water acoustic waveguide with rough boundaries.

ISSN:0001-4966    

DOI:10.1121/1.2022182

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Signal transmission loss and spatial coherence data for source‐receiver separations between 100 and 250 km were acquired in the Gulf of Mexico with a calibrated seismic measurement system (400 m deep), a towed projector (100 m deep) which emitted 67 and 173‐Hz tones, and a moored Webb sound source at 988‐m depth driven at 175 Hz. Environmental data such as the range dependent bathymetry and sound velocity profiles were measured. The 67‐Hz data showed a persistent sound transmission loss of approximately 90 dB whereas the 173 Hz showed several pronounced loss minima between 100–90 dB. Slope enhancements were found to be on the order 2–4 dB at 67 Hz and 6 dB at 173 Hz when compared to flat bottom calculations. Pairwise coherence data show the combined effects of multipath interference and signal‐to‐noise ratio. Estimates of signal coherence length from the coherent summation of streamer hydrophones yield coherence lengths between 70–300 m at a frequency of 173 Hz. Fast asymptotic coherent and normal mode transmission loss calculations produced results consistent with measured data for the deep flat portion of the measurement tracks when measured geoacoustic profiles or related bottom loss curves were used. The implicit finite difference parabolic equation calculations were consistent with range‐averaged data for the flat portion of the track as well as on the slope. These results show that if proper qualitative description of the sub‐bottom velocity profiles axe used, then computations with either a parobolic equation or normal mode technique are consistent with experimental results.

ISSN:0001-4966    

DOI:10.1121/1.2022187

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Transmission loss as a function of depth and range are presented in color contour displays. Black and white contour plots are not as effective compared to the color plots which make the information easier to assimilate. However, the color selection is an important consideration in that it can bias interpretation. The color transmission loss displays can be effectively used to judge quality and significance of the predictions. This is demonstrated in this paper by model comparisons using PE, RAYMODE, and FACT. Predictions from all these models at 500 Hz and 15 kHz in a surface duct environment are presented. The PE model is used to illustrate the effects of sound velocity and bathymetry range dependence. [Work supported by WHOI PO 29518 under NORDA Code 270 Contract N00014‐80‐C‐0381.]

ISSN:0001-4966    

DOI:10.1121/1.2022193

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Computer‐steered microphone arrays provide an attractive sound‐transducing means for interactive communication by sizable groups of talkers. But the spatial acuity of arrays typically varies with frequency, exhibiting diminishing beamwidth as frequency increases. Frequency‐weighting the array is one means to mitigate the variation and to achieve more uniform beamwidth over the useful frequency range. Acoustic low‐pass filtering, accomplished in the array design, provides effective and economical modification of beamwidth.

ISSN:0001-4966    

DOI:10.1121/1.2022194

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Porous ceramics of the PZT type have been found to exhibit very high values of piezoelectricgconstant when compared with the conventional PZT. The material also showed no hysteresis effect upon pressure cycling. These features suggested that porous ceramics may be potentially useful for hydrophone applications. Early prototypes of high‐frequency hydrophone designs containing porous PZT elements were found to have a constant free‐field voltage sensitivity (FFVS) up to about 100 kHz. Above this frequency, however, a sharp decrease in the FFVS was observed. Since variations in the hydrophone design did not improve the high‐frequency response of the hydrophones, the loss in FFVS was attributed to the material itself. A theoretical model was developed to analyze this loss phenomenon in porous ceramic hydrophones. The effect of the porosity was found to reduce the frequency constantNRof the piezoelectric ceramic. The frequency dependence of the strain produced in the porous ceramic by a longitudinal wave was further determined. The general feature of the strain‐versus‐frequency calculation agreed very well with the measured FFVS‐versus‐frequency relation. Since the voltage generated is proportional to the strain in the piezoelectric element, this result is used to explain the observed loss in the FFVS of porous ceramic hydrophones. [This work was supported by the ONR Acoustic Transduction Metrology Program.]

ISSN:0001-4966    

DOI:10.1121/1.2022201

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Quantifying the benefits of noise reduction presents complex methodological difficulties. Appropriate measures of hearing loss at equilibrium as well as adjustment periods need to be expressed in appropriate terms. Nonaudiometric effects of noise exposure, though difficult to quantify, must not be ignored. The effect of worker mobility must be accounted for explicitly. The presentation of the benefits of noise reduction in juxtaposition to the costs must occur in ways which reflect a realistic appreciation of the health problem for which policy alternatives can be designed.

ISSN:0001-4966    

DOI:10.1121/1.2022208

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Past emphasis in industrial noise in the United States has been on reducing the noise of existing machines and plants. This was a direct result of OSHA regulations requiring feasible controls. Much has been accomplished even though the regulations left questions as to what was feasible. The new emphasis on the purchase of more productive machinery and construction of new plants requires that more attention be shifted to the development of quiet new machines and consideration of noise in new plant layout. It is often not feasible to later implement controls which could have been incorporated in new machine or plant designs. Failure to give proper attention to noise of new plants and machines during a period of economic growth will greatly delay the eventual quieting of the workplace. Outside of a few leading companies which have recognized the benefits of noise reduction and active noise control programs, there appears to be little effort to assure quiet in new construction. Those companies which are attempting to buy quieter machines are encountering difficulty as they “go it alone.” This paper will discuss the reasons why more is not being accomplished and actions which could be taken by manufacturers, machine builders, industry organizations, and government to make greater progress possible.

ISSN:0001-4966    

DOI:10.1121/1.2022210

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

The transfer of liquid oxygen (LOX) from a storage vessel to a rocket engine generally requires the use of a pressurizing gas like nitrogen at a typical pressure of 3000 psi. The condensation of gaseous nitrogen to the liquid (LN2), combined with high miscibility, results in contamination of the LOX, which has a deleterious effect on engine performance. It has been proposed to monitor the LOX contamination through sound speed measurements. The purpose of this study is to measure the sound speed of LOX‐LN2mixtures under controlled conditions and to utilize the results in a practical LOX contamination monitor. The measurements, performed by the pulse‐echo technique on several LOX‐LN2compositions, reveal a slight deviation from a linear dependence of the sound speed upon the mole fraction of LN2. The results for pure LOX and pure LN2at − 195.8 °C and 1 atm pressure are 1008.5 ± 0.25% and 852.8 ± 0.32% m/s, respectively, and these are compared to measurements reported in the past.

ISSN:0001-4966    

DOI:10.1121/1.2022218

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP