Change of Pitch with Loudness at Low Frequencies

Abstract

The changes in pitch which result from changes in the loudness of low frequency tones were investigated for several frequencies between 75 and 1000 c.p.s. with a crew of 9 observers. The loudness levels covered the range 20 to 120, and both telephone receivers and a loudspeaker were used as sound sources. Fletcher's pitch standard, a pure tone of loudness level 40, was employed. All consistent judgments gave pitch shifts downward with increasing loudness, but large differences between individuals were found. Two observers perceived no shifts at any frequency or loudness while three others experienced changes greater than 35 percent at the highest intensity. Appreciable changes with time in individual judgments were found. There appeared insignificant difference between data obtained with telephone receivers or with the loudspeaker. A set of contours of equal loudness level, plotted on coordinates frequency and pitch change in percent, is given. These curves show a pitch change small at 1000 cycles, increasing to maximum at a low frequency and decreasing for still lower frequencies. The frequency of greatest shift increased from about 100 cycles at small loudness to about 200 at loudness level 120. The Appendix describes automatic test equipment that greatly simplified the testing routine and improved its accuracy.

Pitch Perception

“…depends upon the period or frequency of the vibrations constituting the sound and upon that alone." Many investigators (60,113,126,167,173,183,199,212) have noted that the pitch of a tone seems to change when its intensity changes --for example, when S is required to reproduce vocally the pitch of a tuning fork (middle C). When the fork is held close to the ear so its intensity is increased, the pitch of the singer's voice is slightly lower (126).…”

“…A great deal of investigation has gone into this problem, and the majority of the studies indicate that, for low tones, the pitch decreases with intensity; and for high tones, the pitch increases with intensity. For certain tones in the middle range (e.g., 2000 cps), there is no change in pitch (60,113,126,167,170,183,199,212).…”

“…It is evident that the pitch change whicn occurs through binaural interaction casts grave doubts upon the hypothesis of the mediation of pitch by the position of maximal stimulation. Furthermore, Snow (167), investigating how low tones change pitch as a function of intensity, found that some of his subjects showed changes, but others did not. Those who did, varied greatly among themselves in the amounts of change, and even a single subject varied from day to day.…”

The sense of pitch and local increase in threshold

“…From the distribution of judgements a frequency of the second tone was found which had the same pitch as the standard tone. A similar method was used to that of Snow (1936).…”

“…Hitherto, in work on the modifying influence of intensity (e.g. Stevens, 1935;Snow, 1936;Morgan, Garner & Galambos, 1951) the subjects have been chosen for their normality of hearing. It is reported by Morgan et al (1951) that it is typical for such subjects to find pitch almost independent of intensity.…”