Synchronization of cubic distortion spontaneous otoacoustic emissions

A spontaneous otoacoustic emission spectrum may contain equally spaced emission peaks. Then, two peaks, at frequencies, f(1) and f(2), respectively, apparently generate a distortion product at f(d)=2f(1)-f(2) [or 2f(2)-f(1)]. For the three emission peaks of nine of such triplets tin six emission spectral, the phases phi(1)(t), phi(2)(t) and phi(d)(t) were computed, respectively. The phase difference Delta phi(t)=phi(d)-(2 phi(1)-phi(2)) [or Delta phi=phi(d)-(2 phi(2)-phi(1))] tends to lock at a plateau value phi(lock) (modulo 2 pi), but occasional jumps up or down nX2 pi to a neighboring plateau. Apparently, the emission at position 2f(1)-f(2) [or 2f(2)-f(1)] synchronizes to the cubic distortion product generated by the primaries f(1) and f(2), but occasionally slips out of the synchronized regime. This behavior is consistent with a model consisting of a self-sustained oscillator in the presence of weak noise, driven by a periodic force. (C) 1998 Acoustical Society of America.