Categorical assessments on fluctuation strength of synthesized sounds

Abstract

Results on category scaled fluctuation strength of different kinds of synthesized signals are presented. Fluctuation can become a major aspect of sound quality, and the intent of the study was to investigate the relationship between ratio-scaled data in literature [e.g., Zwicker and Fastl, Psychoacoustics (Springer-Verlag, New York, 1991)] and categorical judgments. Signals used comprise AM or FM tones with different carrier frequencies (0.25, 0.5, 1, 2, 4, 8 kHz) as well as modulated noises. Modulation frequencies vary from 0.25 to 32 Hz in octave steps. The whole set of 66 stimuli each lasting for 6 s was divided into three sequences presented over headphones in a sound-proof cabin. As in previous roughness assessments [Daniel and Weber, Acustica 83, 113–123 (1997)] judgments were made using an ‘‘analog’’ category scale consisting of five categories (not -, a little -, medium -, rather -, and very fluctuating) which are combined with a continuous scale to overcome limited resolution of the categories. It turns out that the concept of fluctuation is interpreted differently by subjects, especially by ‘‘naives’’ and already trained ‘‘experts.’’ The consequences for the different kinds of noises will be discussed as well as the relationship to ratio-scaled data.