Development and Evaluation of Bone-conducted Ultrasonic Hearing-aid Regarding Transmission of Speaker Emotion: Comparison of DSB-TC and DSB-SC Amplitude Modulation Method

Human listeners can perceive speech signals in a voicemodulated ultrasonic carrier from a bone-conduction stimulator even for sensorineural hearing loss patients. Considering this fact, we have developed a bone-conducted ultrasonic hearing aid (BCUHA). However, there remains considerable scope for improvement, particularly in terms of sound quality. Voice-modulated BCU is accompanied by a strong high-pitched tone and some distortion depending on the amplitude modulation method. In this study, the sound quality of a BCUHA with double-sideband transmitted carrier (DSB-TC) modulation and double-sideband suppressed carrier (DSB-SC) modulation methods was examined. The assessment was conducted by examining the transmission of the emotional state of speakers. The evaluation used emotion-identification experiments. Types of emotion included Ekman’s basic six emotions (“anger,” “disgust,” “fear,” “joy,” “sadness,” and “surprise”) and “neutral.” In addition, a series of subjective evaluations regarding “voice clarity,” “comfortableness,” and “preference” was conducted. The results showed that although DSB-SC sound was superior in “comfortableness” and “preference,” voice emotion transmission was more effective in DSB-TC conditions.