Jitter, shimmer, and noise in pathological voice quality perception

Although jitter, shimmer, and noise characterize all voice signals, their perceptual importance has not been established psychoacoustically. To determine which of these acoustic attributes is important in listeners’ perceptions of the inharmonic component in pathologic voices, copies of natural pathological voices were synthesized parametrically using seven different models of the inharmonic part of the voice source: jitter only, shimmer only, noise only, jitter plus shimmer, jitter plus noise, shimmer plus noise, and jitter plus shimmer plus noise. Listeners then compared pairs of these stimuli and judged whether they were the same or different. Listeners also compared synthetic and natural stimuli, to determine the extent to which different aspects of the inharmonic part of the source improved or worsened the quality of the match to the original natural voice sample. Preliminary results suggest that jitter and shimmer may not be perceptually important features of most pathological voices, despite their long history as acoustic measures of voice. In contrast, it appears that listeners perceive spectrally shaped additive noise as the critical inharmonic acoustic element contributing to pathologic voice quality. [Research supported by NIDCD.]