Scaling the perceived fluctuation strength of frequency-modulated tones

Abstract

Fluctuation strength is one of the major psychoacoustic variables considered in sound-quality evaluation. Zwicker and Fastl [Psychoacoustics (Springer, Berlin, 1999)] summarize recommendations for its computation, which have already been implemented in various software applications, even though the data basis is rather limited. In particular, the dependency of fluctuation strength on modulation frequency and modulation depth has seemingly never been tested in a factorial design. Therefore, in experiment I both of these factors were varied simultaneously in order to create 54 different frequency-modulated sinusoids. The task of the subjects was to directly estimate the perceived magnitude of fluctuation strength. The results do not conform well with the prevalent model of fluctuation strength. In experiment II this finding was further investigated by varying only one factor at a time. The results show that large individual differences, particularly in the effect of modulation frequency, persist. Thus, in experiment III the interaction of both factors was analyzed on an individual basis. By employing a 2AFC procedure, matches in fluctuation strength were obtained. The results suggest that most listeners are not able to integrate modulation frequency and modulation depth additively into a unidimensional percept. [Work supported by Centercontract on Sound Quality, Aalborg University.]