Volume 24, Issue 4, July 1952
Index of content:
- PROGRAM OF THE FORTY-THIRD MEETING OF THE ACOUSTICAL SOCIETY OF AMERICA
- Session B. Psychoacoustics and Hearing
- Contributed Papers
24(1952); http://dx.doi.org/10.1121/1.1917474View Description Hide Description
Two or three pairs of nichrome steel electrodes (20μ) are inserted into each of two or three turns of the cochlea of guinea pig. One electrode of each pair is in scala tympani, one is scala vestibuli. Such “differential” leads record nearly pure cochlear microphonics from segments of the cochlear partition only about 1 mm long. Low tones evoke microphonics from all four turns; but as the frequency is increased (holding the response from the basal turn constant by adjusting the intensity of sound), the microphonic ceases, first at the apical turn, then at the third turn, and finally at the second turn. The normal space pattern for each frequency as revealed by its cochlear microphonic is a long plateau rising slowly from the basal end but with a much more abrupt fall toward the apex. The locus of this abrupt fall is characteristic for each frequency. The space-timepattern of an acoustic signal is a decelerating traveling wave moving from base toward apex. The velocity of a 500-cycle wave falls from about 70 m/sec in the basal turn to about 2 m/sec near the helicotrema. These electrical patterns are in general agreement with the mechanical patterns described by Békésy.
The space and space-time patterns remain normal even when large sections have been removed from the bony shell of the second turn, over both scala vestibuli and scala tympani. The traveling wave still originates in the basal turn even when the cochlea is stimulated by sound transmitted through the fluid in a small pipette that enters scala vestibuli of the third turn through a hole in the bony shell.
- Session D. Psychoacoustics and Speech Communication
24(1952); http://dx.doi.org/10.1121/1.1917485View Description Hide Description
Because of the statistical nature of speechsounds, time-exposure photographs of the display on a Panoramic Analyzer can be used as high speed acoustic spectrograms of impulsive sounds. For speech systems, the analyzer is modified to sweep at the syllable articulation rate. The photographs can be interpreted to show quantitatively a number of characteristics of speech communication systems. So far, this process has been applied to the study of the characteristics of speech recordings and in the calibration of speech audiometers.
24(1952); http://dx.doi.org/10.1121/1.1917487View Description Hide Description
Pitchdiscrimination data for pure tones have been obtained for two trained subjects at frequencies of 250, 1000, and 4000 cps. Two psychophysical procedures were used: In one method (Munson and Gardner's ABX procedure) the subject votes whether the third in a series of three tones sounds more like the first or the second of the series. In the second method (used extensively by Harris) the subject is presented with a standard tone followed by a test tone, and he judges whether the test tone is higher or lower than the standard. The difference limens measured by the second method are for both subjects smaller (by a factor of two or more) than those found by the ABX procedure. This fact gains in significance since one subject has small DLs while the other has rather large ones. Judgmental data obtained from a limited choice situation can provide at best an upper bound for so-called ultimate sensory capacity. Practically speaking, the second method not only yields smaller DLs, but is also easier on the subjects, who can form the discrimination relatively quickly.
24(1952); http://dx.doi.org/10.1121/1.1917488View Description Hide Description
Synthetic vowel sounds, formed by electrical excitation of resonant circuits by a regular series of impulses, have been used as stimuli in a group of psychophysical experiments. The experiments include measurements of just noticeable differences (JNDs) in formant frequency and in band width for the synthetic sounds with one and two resonances, and with resonance band widths comparable to those found in measuredvowel spectra. Average JNDs in formant frequency and band width at 1000 cps are 17 cps and 25 cps, respectively. The results are used to establish a frequency scale for the representation of vowelformants. Equal distances on this scale correspond to an equal number of JNDs in formant frequency. The proposed scale is approximated more closely by a linear frequency scale than by a mel scale. The approximate number of JNDs between pairs of vowels (arranged on a scale from front to back vowels) is evaluated, and is in the range 15–20 on the average. In general, the data indicate that frequency analysis of vowels using a filter band width as narrow as 45 cps provides more information than the perceptual processes can resolve.
24(1952); http://dx.doi.org/10.1121/1.1917489View Description Hide Description
In a recent paper, the present authors described the effects upon masking of varying the interaural phase positions of a 500∼ tone and of the 500∼ masking component of a white noise. The present paper extends this work by displacing the masking noise in time. This is accomplished by moving one head of a binaural tape reproducer. The results are in agreement with those previously published on the masking of tones by noise, and support the idea of a “critical” band. They also furnish additional evidence of the importance for masking level difference, of the interaural noise correlation.
24(1952); http://dx.doi.org/10.1121/1.1917490View Description Hide Description
At the end of World War II the introduction of a wide variety of extremely noisy aircraft flying very long missions at high altitudes had placed demands on interphone communications that the old system could not meet. Beginning in 1947 an entirely new system was developed with the close and active cooperation of the Air Materiel Command (now Wright Air Development Center). The criterion of performance is the word articulation of the entire system. New microphones, headsets, loudspeakers,amplifiers, control panels, and power supplies were developed. The resulting system has a frequency range of 200–6000 cps. It is very flexible, extremely comfortable, and provides high word articulation scores in 120-db sound fields at altitudes up to 35,000 feet.
24(1952); http://dx.doi.org/10.1121/1.1917491View Description Hide Description
A screening audiometer has been developed, which functions automatically. It has the following salient features: The subjects are required to make simple numerical choices as indicated by visual instructions. A single numerical choice for each frequency serves to evaluate the two ears separately. The stimuli consist of interrupted tones of pre-set levels. The operation of this instrument and the results of the field tests are presented.
24(1952); http://dx.doi.org/10.1121/1.1917492View Description Hide Description