Study on the perceptual effects of fine and global fluctuations in the fundamental frequency of singing voice

Our research aims to reveal how the auditory system perceives the fundamental frequency (fo) of the singing voice including vibrato. This study investigates the effects of fine and global fluctuations in the fo trajectory on auditory perception through subjective experiments. In these experiments, it is desirable to control fine and global fluctuations in the stimuli parametrically. To achieve this, we propose a method to generate such stimuli by filtering the fo trajectory. Instead of directly extracting and modifying the fine and global fluctuations via filtering, our method adjusts the impulse responses of low-pass and high-pass filters. First, we design two filters with cutoff frequencies chosen so that the sum of their frequency responses is approximately flat. The low-pass and high-pass filters are designed to isolate the global and fine fluctuations, respectively. Second, each impulse response is scaled by a weighting factor, and the composite filter’s impulse response is obtained by adding them together. Finally, the modified fo trajectory is generated by convolving the composite impulse response with the original trajectory. In a preliminary experiment, a stimulus with reduced fine fluctuation was perceived as similar to the original. In contrast, the stimulus with reduced global fluctuation was perceived as significantly different. These results suggest that global fluctuation in the fo trajectory has a stronger effect on auditory perception than fine fluctuation.