Design and preliminary evaluation of electrolarynx with F0 control based on capacitive touch technology

An electrolarynx (EL) is one of the most popular voice rehabilitation technologies used after laryngectomy. However, most ELs generate monotonic EL speech, which has been shown to create a particular deficit in speech intelligibility, especially for Chinese Mandarin (Mandarin). Mandarin is a tonal language that makes lexical distinctions using variations in tone. Our purpose is to design an EL that can produce the four Mandarin tones, and to evaluate its performance. We designed a fundamental frequency (F0) control method for Mandarin EL speech and manufactured a touch-controlled electrolarynx (T-EL) prototype. Using monosyllables, disyllabic words, and frequently used phrases, we evaluated speech produced with a T-EL, as well as with monotone (M-EL) and variable-frequency modes (P-EL) of a commercially available TruTone EL. A male native Mandarin speaker with laryngectomy volunteered to be the speaker. Results show that the normal speech pitch contours of the four Mandarin tones were most closely matched by the characteristics produced with T-EL. The statistical accuracy of the T-EL's tone and word perception was significantly higher than that of the other EL types. Moreover, the confusion matrix indicates that the listeners could correctly identify the tones of monosyllables and disyllabic words in T-EL speech. Accurate tone judgment can improve the intelligibility of EL speech in Mandarin. The mean opinion score was used to evaluate the listeners' acceptability of EL speech. The scores of the T-EL and M-EL were very close, and the score of the P-EL was significantly lower than that of the other two ELs. However, the results from a single speaker cannot provide sufficient data to conclude which EL has a higher acceptability. The evaluation of multiple EL speakers with different EL types at difference levels of proficiency should be studied in future research.