Pitch of Frequency-Modulated Signals

Abstract

The pitch of quasi frequency-modulated signals consisting of only 3 frequency components was determined. Such a signal was generated by modulating a sinusoid of central frequency f with a second sinusoid of frequency g and shifting the phase of the center-frequency component over 90 deg. Listening experiments showed that, with a ratio n=f/g [greater than] or equ 9 and a modulation index m=2, a better tonality was achieved for odd values of n than for even values. Moreover, the frequency values for pitch were found to vary as a function of the modulation index m. This was investigated at a central frequency of 2000 cps. The pitch values found are in good agreement with those calculated from the hypothesis that the distance between 2 positive peaks in the fine structure near 2 adjacent crests of the envelope of the signal constitutes a measure of the pitch of the complex. An explanation is also given for the experimental evidence of a purely frequency-modulated signal giving rise to a low pitch sensation.