Pitch Variations Arising from Certain Types of Frequency Modulation
Don Lewis, Milton Cowan, Grant A. Fairbanks · The Journal of the Acoustical Society of America · 1937
This report deals with an investigation of the pitch of sounds characterized by frequency modulation. It has to do mainly with the perceived extent of pitch glides. By means of a specially-designed variable condenser the frequency of an oscillator could be modulated, intensity of output remaining essentially constant. Either sinusoidal or linear modulation could be obtained, and the amount and rate of modulation were both subject to control. It was possible to secure, among others, the following types of variation: (a) isolated frequency sweeps, either upward or downward in direction; (b) upward-downward or downward-upward sweeps; (c) sweeps, either upward or downward, at the beginning or end of a steady-state sound; (d) periodic modulation, that is, frequency vibrato. Sounds with vibrato were studied only casually. The experimental data, which reveal the relationship between perceived extent of glide and both the amount and the rate of frequency modulation, are interpreted to indicate their bearing on problems of pitch perception in speech and music. The results are further shown to have a significant bearing on auditory theory in that they reveal the great rapidity with which the ear responds to sounds of continuously varying frequency.