Restructures the vocal cords and introduces a secondary set of vocal folds modeled on songbird syrinx architecture, allowing the user to produce two independent tones simultaneously. The result is a voice capable of natural harmonic singing — overtone chords, dual-pitch speech, and vocal effects impossible for an unmodified human larynx. The modification is valued by musicians, performers, and public speakers. A secondary application is vocal frequency manipulation — trained users can produce infrasonic and ultrasonic components in their speech that cause physiological responses in listeners (unease, calm, attention) without the listener understanding why. Zheng-Dao Bioelectric markets the infrasonic capability as a 'persuasion enhancement' for corporate negotiators, which has drawn ethical scrutiny.