Like a breeze stirring the leaves, the layered voice evokes the gentle sounds of nature— a sonic weaving of self, shaped into ambient sound. By including ultrasonic frequencies exceeding 20kHz, the vibrations extend beyond the reach of hearing, quietly seeking resonance with unseen aspects of nature, beyond the contours of conscious perception.

"Yusei" (湧声) refers to a voice that wells up like an underground spring— a tremor before language, gently drawn into sound. It is not merely heard, but sensed; a form of sound that traces the threshold of perception, subtly trembling in the space between self and world.

[ Technical Note｜Acoustic Analysis Supplement ]
An analysis of the vocal frequency and acoustic characteristics used in this work was conducted by the Japan Acoustic Research Institute. The following properties were identified:
・The frequency components of the voice extend into the ultrasonic range beyond 20kHz, surpassing the limits of human hearing.
・Resonant amplification was observed across approximately 2000Hz, 3000–5000Hz, 7500–11000Hz, and 12000–17000Hz.
・This type of acoustic structure is considered similar in nature to phenomena found in the natural world, such as the sound of wind rustling through leaves.
These findings suggest that the sound embodied in “Yusei” is not merely meant to be heard, but to gently touch the deeper layers of perception.