Effect of consonant enhancement in reducing mishearing of Japanese synthesized speech monosyllables

Consonants are crucial for effective communication but often pose challenges for individuals with hearing impairments or age-related hearing loss. Enhancing consonant perception improves intelligibility and reduces cognitive load; however, traditional methods like vowel suppression and spectral shaping often compromise speech naturalness. Japanese phonetics, with its predictable vowel-consonant structures, provides a unique context for studying consonant enhancement, particularly in synthetic speech, which frequently suffers from perceptual confusion and acoustic limitations. This study focuses on improving the intelligibility of /bi/ and /gi/, which are commonly misheard as /ri/ in synthetic speech. Using speech generated by Amazon Polly and Google Text-to-Speech, we applied various enhancement techniques, including amplitude amplification and waveform manipulation targeting specific acoustic regions. Through three experiments, critical time segments for consonant intelligibility were identified, and the effects of enhancements were evaluated. Results showed that amplifying the initial consonant region (R1) significantly improved intelligibility, whereas truncating mid-waveform regions (R2) reduced clarity. Platform-specific differences in processing algorithms also influenced the effectiveness of these enhancements. These findings underscore the importance of tailored signal processing strategies for synthetic speech. Future research should explore adaptive enhancements and extend investigations to more complex speech contexts, aiming to optimize synthetic speech systems for individuals with hearing impairments and older adults.