In this work, we present our attempt to create sounds that are perceived as vowels while inducing pitch-circular auditory illusions, in which a cyclic sequence of tones gives the perception of endlessly ascending or descending pitch. Traditionally, such illusions have been created using synthetic sinusoids, such as Shepard tones. Achieving both vowel perception and the illusion of an infinite pitch scale remains a significant challenge. To this end, we propose a transformation method for a given vowel sound, which manipulates the fundamental frequency while preserving the spectral envelope of the original vowel. In addition, we apply pitch-dependent harmonic attenuation to control the perceptual salience of octave-related tones, based on findings from prior work Deutsch 2008. Subjective listening experiments using five Japanese vowels confirm that the proposed method maintains high vowel identification accuracy while producing an illusion of pitch circularity. We also present a demo of synthesized singing voices using the proposed transformation.
Hashimoto et al. (Wed,) studied this question.