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UBC Theses and Dissertations

The acoustic and perceptual effects of single-microphone noise reduction in hearing aids on Mandarin fricatives and affricates Chong, Foong Yen


Single-microphone noise reduction (SMNR) is implemented in hearing aids to suppress background noise. The noise-like feature in fricatives and affricates is susceptible to SMNR processing when background noise is present. Most SMNR studies have examined English speech materials but very few have examined Mandarin fricatives and affricates. In the present research, three studies were conducted to examine the acoustic and perceptual effects of SMNR on Mandarin fricatives and affricates. Study 1 aimed to test the validity of the inversion technique as a tool for separating speech and noise signals recorded from hearing aids in sound field. Study 1 showed that the inversion technique is a feasible and reliable tool for separating speech and noise post hearing-aid processing. However, fidelity of the retrieved speech signals showed variability between hearing aids. The acoustic effects of SMNR on Mandarin and English fricatives and affricates were examined in Study 2. Speech-plus-noise signals were presented to and recorded from one of two hearing aids mounted on a manikin, under SMNR-on and SMNR-off conditions. Speech signals were retrieved for subsequent acoustic analysis. The results showed that SMNR processing did not produce substantial acoustical changes in the temporal and spectral domain as measured in the Hearing Aid Speech Quality Index. Spectrographic analysis showed a reduction in frication-noise and release-burst intensity, and changes in the spectral mean. In Study 3, the Mandarin retroflex fricative and affricates, processed with and without SMNR, were used to examine the effects of SMNR on novel speech sound identification in noise by naïve listeners. Native English talkers might rely on bottom up processing to categorize the Mandarin retroflex sounds because these sounds were not in the English phonemic inventory. All listeners underwent five sessions of identification training and testing. The results showed that SMNR did not degrade the identification of novel speech sound in naïve listeners. Significant contributions of the present research are (i) the acoustic effects of SMNR on Mandarin and English fricatives and affricates were systematically documented and (ii) provided further evidence on SMNR having no effect on speech perception in noise.

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