Influence of time-varying pitch on timbre: “Coherence and incoherence” based on spectral centroid

In this paper, the effect of time-varying pitch-glides on timbre perception of vowels is studied experimentally. While earlier studies show that stationary pitch is observed to be a significant dimension of timbre, we explore the effect of non-stationary pitch changes on the perception of vowel timbre using synthesized vowels. In each trial, three listeners rate perceptual timbre change using a MUSHRA-like (MUltiple Stimuli with Hidden Reference and Anchor) methodology. Results show that perceived timbre change is affected by the pitch-shift and nature of pitch-glide. Timbre change is observed to be monotonic with pitch-shift for all types of pitch-glides, implying larger the pitch-shift, higher the perceived timbre change. When the excitation is a pitch-glide, the vowel spectral centroid and the nature of pitch-glide interact. We observe that for vowels of higher spectral centroid, decreasing pitch-glides cause higher timbre change than the timbre change caused by increasing pitch-glides; vice- versa for vowel of lower spectral centroid. Thus, “incoherent” pitch-glides cause higher timbre change than the “coherent” pitch-glides.