William A. Yost
Sandra J. Guzman
Stanley Sheft
Parmly Hear. Inst., Loyola Univ. Chicago, 6525 N. Sheridan Rd., Chicago, IL 60626
A cascade of add, delay (d ms), and attenuate (-1(less than or equal to)g(less than or equal to)1) circuit excited with noise produces iterated rippled noise (IRN) stimuli. The matched pitch and discriminability between pairs of IRN stimuli were studied as a function of g, d, and the number of circuit iterations (n). For g>0, the pitch of all IRN stimuli equals 1/d. For g<0, pitch depends on n: For small n, there were two pitches in the region of 1/d, while for large n there was a single pitch equal to 1/2d. Peaks in the autocorrelation function of IRN stimuli accounted for all of the results. Peaks in the autocorrelation functions for IRN stimuli indicate the number of intervals in the waveform with durations pd (p=1,2,...,n), and for g<0 intervals related to peaks near 1/md (m=odd integers) caused by assumed auditory filtering. The number of intervals (i.e., the heights of the autocorrelation peaks) determines the discriminability between IRN stimuli, while the reciprocal of the interval duration determines the matched pitch. These results support a temporal rather than a spectral account of the pitch of IRN stimuli. [Work supported by NIH.]