Contribution of Fundamental Frequency to Perceived Vocal Roughness: Evidence From Time-Scaled Natural Voice Samples.

OBJECTIVES

Fundamental frequency (fo) influences auditory roughness in psychoacoustic paradigms; however, it remains unclear how changes in fo alone, when applied to dysphonic voices, alter perceived vocal roughness and breathiness. We investigated how roughness and breathiness change when fo is systematically manipulated in dysphonic voices while maintaining the time-domain waveform shape.

METHODS

Natural sustained vowels from dysphonic or nondysphonic speakers were resynthesized in Praat by time-scaling so that fo was converted from the original value to a target fo of 50, 100, or 200 Hz without altering the overall waveform shape (Experiment 1). In Experiment 2, an extended low-fo set was created by converting fo to 30-100 Hz in 10-Hz steps. Experienced raters evaluated each token for roughness and breathiness. Linear mixed-effects models tested whether changes in fo predicted perceptual ratings after accounting for within-token and between-rater variability. Receiver operating characteristic (ROC) analysis was used to identify an fo cutoff associated with higher roughness in Experiment 2.

RESULTS

Across experiments, lowering fo systematically increased roughness ratings, whereas breathiness showed comparatively smaller and less consistent changes. In mixed-effects models, fo was an independent predictor of roughness but not of breathiness. In Experiment 2, ROC analysis identified an fo threshold of 70 Hz for differentiating higher versus lower roughness. These patterns are consistent with auditory accounts in which reduced harmonic spacing relative to cochlear bandwidths enhances within-band interactions and temporal-envelope modulation.

CONCLUSIONS

By manipulating fo while preserving waveform shape, we identified an auditory contribution of fo to perceived vocal roughness that is largely distinct from breathiness. These findings support the development of acoustic roughness indices that account for fo-dependent harmonic spacing and critical-band envelope modulation, and they underscore the need to consider fo when interpreting auditory-perceptual roughness ratings.