Development of an Electrolarynx Capable of Supporting Tonal Distinctions in Mandarin

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 voice box, 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 (EL) 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 userinterfaces which make it hard for pitch-changing during speaking, especially for tonal languages. This senior design project focuses on developing an ELbased 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 to let user select and produce the tones necessary to converse in Mandarin. The gyroscope is embedded into a custom-made EL 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 EL system and understandable speech with multiple syllables. USER INTERFACE In order to give electrolarynx patients the ability to voice tonal distinctions necessary for Mandarin, an embedded electrolarynx system was used to let the user choose the tones he or she would want to voice so that conversational Mandarin would be possible. A gyroscope-based user interface was implemented inside the body of the EL system. The user would hold the system against his neck at a particular position in order to calibrate the system and then move the electrolarynx body around in four distinct axes in order to activate the four different tones of Mandarin.