Development of an Electrolarynx Capable of Supporting Tonal Distinctions in Mandarin

Abstract

Tone distinction is a vital part of languages such as Mandarin, where the same words said in different tones could mean vastly different things. For people who have lost their voicebox, usually due to the cancer of the larynx, making this tone distinction becomes impossible with currently available Electrolarynxes which are limited to monotones. Further, due to a lack of tone distinction, the resulting voice sounds ‘robotic’ and unnatural. Wan et. al recently developed an electrolarynx capable of tonal control using a trackball, and TruTone® from Griffin Laboratories is another EL that features tone modulation via capacitive buttons. These designs feature user-interfaces which make it hard for pitch-changing during speaking, especially for tonal languages. This senior design project focuses on developing an Electrolarynx-based system capable of modulating vocal frequencies so that tonal distinctions can be made for Mandarin. We have developed a novel user interface using a gyroscope so that an electrolarynx user might be able to select and produce the tones necessary to converse in Mandarin. The gyroscope is embedded into a custom-made electrolarynx body along with a microcontroller (ATMEGA328) and additional circuitry for digital-to-analog conversion, voltage-controlled oscillation and amplification. Our system is capable of accurately reproducing the four tones in Mandarin, along with the fifth ‘non-tone’ as well as taking care of tone transition rules in Mandarin. Initial results have shown as much as 90% accuracy in the identification of the four individual tones produced by our Electrolarynx system and understandable speech with multiple syllables.