ISSN:0001-4966    

DOI:10.1121/1.1916405

出版商:Acoustical Society of America    

年代:1947

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1916406

出版商:Acoustical Society of America    

年代:1947

数据来源: AIP

摘要:

The characteristics of speech, hearing, and noise are discussed in relation to the recognition of speech sounds by the ear. It is shown that the intelligibility of these sounds is related to a quantity called articulation index which can be computed from the intensities of speech and unwanted sounds received by the ear, both as a function of frequency. Relationships developed for this purpose are presented. Results calculated from these relations are compared with the results of tests of the subjective effects on intelligibility of varying the intensity of the received speech, altering its normal intensity‐frequency relations and adding noise.

ISSN:0001-4966    

DOI:10.1121/1.1916407

出版商:Acoustical Society of America    

年代:1947

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1916408

出版商:Acoustical Society of America    

年代:1947

数据来源: AIP

摘要:

Articulation tests were conducted to assess the advantages of premodulating clipping inA Mvoice transmitters. The results show that a saving of as much as 14 decibels in carrier power can be achieved, without loss in intelligibility, if the speech wave is first subjected to 24 decibels of peak clipping and then reamplified by 24 decibels in order to obtain 100‐percent peak modulation. Three obvious advantages result from this procedure: (1) the effective range of a given transmitter is increased, (2) overmodulation is permanently prevented, and (3) interference to communications on adjacent frequency channels is eliminated. Realization of this third advantage requires the introduction of a low‐pass filter between the clipper and the point of modulation. Excessive amounts of premodulation clipping should be avoided whenever speech quality is an important consideration and whenever the microphone picks up large amounts of ambient noise. On the other hand, when communication is impaired by ambient noise and atmospheric static at the receiver location, large amounts of premodulation clipping serve to maximize intelligibility.

ISSN:0001-4966    

DOI:10.1121/1.1916409

出版商:Acoustical Society of America    

年代:1947

数据来源: AIP

摘要:

The sound field behind a circular disk in the presence of a point source of sound on its axis, is computed approximately. The calculation is based on the reduction of the Kirchhoff surface integral to a line integral by the Maggi Transformation. The predictions of the Kirchhoff theory are compared with a more accurate calculation which makes use of the Green's function. The theory is compared with accurate measurements of the sound field, and satisfactory qualitative and quantitative agreement is found.

ISSN:0001-4966    

DOI:10.1121/1.1916410

出版商:Acoustical Society of America    

年代:1947

数据来源: AIP

摘要:

An earlier paper described the distribution of sound pressure in the auditory canals of a number of subjects in a plane progressive sound field. At a given frequency, the ratio of the sound pressures at the eardrum and at the entrance to the ear canal was found to be greater than unity and essentially independent of the orientation of the observer with respect to the sound source, as might be expected from theory. With this ratio known, it is possible to determine, with relative ease, the sound pressures at the eardrum as a function of azimuth from pressure measurements near the entrance to the auditory canal. By positioning a probe microphone at the entrance to the ear canal and comparing the sound pressures there with the free‐field pressures at the subject's location an estimate of the obstacle effect of head and pinna is arrived at. Adding the known pressure increase in the auditory canal yields a measure of the total obstacle effect of the human head and auditory canal. The subjects were placed in front of a loudspeaker in a room essentially free from acoustic wall reflections. The measurements of the sound pressure at the entrance of the left auditory canal and in the free field in the absence of the subject were carried out by means of a small probe microphone in the frequency range extending from 200–6000 c.p.s. A range of azimuths of 360 degrees was covered in 45‐degree steps. If it is assumed that the two auditory canals are alike and that the head is symmetrical about the median plane, the ratio of the sound pressures at the left and right eardrums can be readily computed from these data. This ratio is of importance in the mechanism of binaural localization. The average for six male subjects was compared with the values obtained by Sivian and White from threshold measurements and was found to be in fair agreement.

ISSN:0001-4966    

DOI:10.1121/1.1916411

出版商:Acoustical Society of America    

年代:1947

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1916412

出版商:Acoustical Society of America    

年代:1947

数据来源: AIP

摘要:

Some properties of wave fronts or constant‐phase surfaces in the acoustic field of a piston‐like source are deduced from an approximate expression for the velocity potential. The calculations are limited to certain ranges of frequencies, piston sizes, and distances from the source, of chief interest in supersonics. The results comprise for plane pistons (a) a determination of the place where the wave fronts reverse their curvature from converging to diverging shape; (b) a calculation of the radius of curvature of the fronts at moderately large distances from the source; (c) an approximate theoretical equation for the shape of the wave fronts, which permits plotting the paraxial portion of these surfaces at medium and large distances. For a concave piston, calculations similar to those of (a) are made. A few comparisons with experimental results are given under (a), (b), and (c). Agreement is qualitative to semi‐quantitative.

ISSN:0001-4966    

DOI:10.1121/1.1916413

出版商:Acoustical Society of America    

年代:1947

数据来源: AIP

摘要:

A limiting factor in the reproduction of disk recordings with a modern reproducer is the tracing distortion arising from the finite size of the reproducing stylus. The sharpest groove modulation which can be reproduced is that having a radius of curvature slightly larger than the tip radius of the reproducing stylus. It is, therefore, desirable to monitor the cutting of disk records with a meter whose indication is based upon this curvature limitation, rather than with a conventional volume indicator. When using a volume indicator alone, overmodulation by as much as 20 db is possible. The theory and construction of such a curvature meter are discussed in this paper.

ISSN:0001-4966    

DOI:10.1121/1.1916414

出版商:Acoustical Society of America    

年代:1947

数据来源: AIP