Perceived principal pitch of FM-AM tones as a function of the phase difference between frequency modulation and amplitude modulation

"FM-AM tones" are defined as vibrato tones whose frequency and amplitude are periodically modulated by an identical waveform simultaneously. "Principal pitch" is steady and average pitch perceived from vibrato tones with periodic pitch fluctuation. The principal pitch shift of FM-AM tones is supposed to be predicted by the pitch averaging mechanism model containing the weighting process with amplitude fluctuation. However, this model is proposed on the basis of the previous experimental results when the phase difference between FM (frequency modulation) and AM (amplitude modulation) is 0 and 180 degrees. In order to make valid the generalization of this model, the principal pitch shift of FM-AM tones was measured when the phase difference between FM and AM is varied from 0 to 315 degrees at a interval of 45 degrees by the psychoacoustical experiment using a method of adjustment. Under the condition that the modulation waveform is sinusoidal and the modulation rate is 7 Hz, the measured principal pitch shift is well predicted by the weighted pitch averaging mechanism model. Moreover our experimental results support the existence of independent processing channels for frequency and amplitude modulation.