Spectral contrast analyses of vowels processed through a multichannel simulated hearing aid

Hearing aids are designed to separate the audible frequency response into independent channels so that gain can be modulated correspondingly, based on the degree and configuration of the hearing loss. However, increasing the number of channels and employing fast-acting compression might lead to the spectral flattening of speech segments. In this study, we performed spectral contrast analyses on three vowels /i, oo, u/ spoken by two male and two female talkers in a /CVC/ context. The initial consonant consisted of /p, b, t, d, k, g, s, sh/ and the final consonant consisted of /t/. Each /CVC/ word was spoken in the phrase, “I said /CVC/, again” Each phrase was then processed by a simulated hearing aid having 2, 4, 8, and 16 independent channels according to an amplification scheme (linear, compression [fast-fast, slow-slow, fast-slow]). Findings revealed that spectral contrast decreased (1) as the number of channels increased, (2) when a fast attack time was employed, and (3) when the talker was a male. Further, significant spectral flattening and shifts in vowel formants occurred for /i, oo/ compared to /u/. We discuss these findings relative to the speech-intelligibility performance of impaired listeners.