TEMPORAL DYNAMICS OF PITCH STRENGTH IN REGULAR INTERVAL NOISES

The pitch strength of rippled noise and iterated rippled noise has rec ently been fitted by an exponential function of the height of the firs t peak in the normalized autocorrelation function [Yost, J, Acoust. Se c. Am. 1001 3329-3335 (1996)]. The current study compares the pitch st rengths and autocorrelation functions of rippled noise (RN) and anothe r regular-interval noise, ''AABB.'' RN is generated by delaying a copy of a noise sample and adding it to the undelayed version. AABB with t he same pitch is generated by taking a sample of noise (A) with the sa me duration as the RN delay and repenting it to produce AA, and then c oncatenating many of these once-repeated sequences to produce AABBCCDD .... The height of the first peak (hl) in the normalized autocorrelati on function of AABB is 0.5, identical to that of RN. The current exper iments show the following: (1) AABB and RN can be discriminated when t he pitch is less than about 250 Hz. (2) For these low pitches, the pit ch strength of AABB is greater than that for RN whereas it is about th e same for pitches above 250 Hz. (3) When RN is replaced by iterated r ippled noise (IRN) adjusted to match the pitch strength of AABB, the t wo are no longer discriminable. The pitch-strength difference between AABB and RN below 250 Hz is explained in terms of a three-stage, runni ng-autocorrelation model. It is suggested that temporal integration of pitch information is achieved in two stages separated by a nonlineari ty. The first integration stage is implemented as running autocorrelat ion with a time constant of 1.5 ms. The second model stage is a nonlin ear transformation. In the third model stage, the output of the nonlin ear transformation is long-term averaged (second integration stage) to provide a measure of pitch strength. The model provides an excellent fit to the pitch-strength matching data over a wide range of pitches. (C) 1998 Acoustical Society of America. [S0001-4966(98)05110-8].