Abstract:

Three-interval forced-choice adaptive procedures were used to estimate difference limens (DLs) for signals with either frequency perturbation (jitter) or amplitude perturbation (shimmer). A time-domain synthesis technique was used to generate sinusoidal and triangular waves with specified amounts of both perturbation types (defined as the mean absolute value, in percent, of the first-order perturbation function) for each of two mean fundamental frequencies (100 and 200 Hz). Standard stimuli had neither frequency nor amplitude perturbation. Sequential characteristics of the signals were determined via autocorrelation analyses. Signals were 900 ms in duration and were presented monaurally at 80 dB SPL via insert earphones to ten listeners with normal hearing. Up to 12 estimates were obtained for each of the eight signal types. Group average DLs ranged from 0.07% (frequency perturbation, 200-Hz triangular wave) to 6.20% (amplitude perturbation, 100 Hz triangular wave). For a given fundamental frequency and waveshape, DLs were smaller for frequency perturbation than for amplitude perturbation. Within a perturbation type, DLs were smaller for triangular waves with frequency perturbation and for sine waves with amplitude perturbation. [Work supported by The University of Georgia Research Foundation.]