When we listen to vibrato tones, we perceive not only frequency fluctuation but also somewhat steady pitch. This pitch sensation of vibrato tones is defined as “principal pitch.” The principal pitch of vibrato tones is located around its carrier frequency, by a method of adjustment. As the location of principal pitch of vibrato tones has the width proportional to its extent of frequency changing, it is impossible to be located more precisely. The principal pitch of symmetrical trill tones is located around its carrier frequency, too. The location of principal pitch of asymmetrical trill tones is shifted in the direction of the longer one between high frequency interval and low frequency interval. This means that the location of principal pitch of frequency modulated tones is defined not only by higher and lower extremes of modulation extent but also by the whole process of frequency changing. It is more shifted than the simple time average of frequency changing. From these experimental results we suppose the pitch averaging mechanism in the auditory process to perceive principal pitch of frequency modulated tones. In this process, this mechanism samples pitch changing continuously, registers in sensory store, and averages every certain moment. When a pitch distribution of frequency modulated tones is asymmetrical, this mechanism accomplishes its function after emphasizing the large part of the distribution. PACS number: 43. 66. Hg, 43. 75. Bc.
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