Introduction: Modulation-based noise reduction (MBNR) is one of the common noise reduction methods used in hearing aids. Gain reduction in high frequency bands may occur for some implementations of MBNR and fricatives might be susceptible to alteration, given the high frequency components in fricative noise. The main objective of this study is to quantify the acoustic effect of MBNR on /s, z/. Methods: Speech-and-noise signals were presented to, and recorded from, six hearing aids mounted on a head and torso simulator. Test stimuli were nonsense words mixed with pink, cafeteria, or speech-modulated noise at 0 dB SNR. Fricatives /s, z/ were extracted from the recordings for analysis. Results: Analysis of the noise confirmed that MBNR in all hearing aids was activated for the recordings. More than 1.0 dB of acoustic change occurred to /s, z/ when MBNR was turned on in four out of the six hearing aids in the pink and cafeteria noise conditions. The acoustics of /s, z/ by female talkers were affected more than male talkers. Significant relationships between amount of noise reduction and acoustic change of /s, z/ were found. Amount of noise reduction accounts for 42.8% and 16.8% of the variability in acoustic change for /s/ and /z/ respectively. Conclusion: Some clinically-available implementations of MBNR have measurable effects on the acoustics of fricatives. Possible implications for speech perception are discussed.

One of the most frequent complaints of individuals with hearing impairment is listening comfort in noisy environments. In order to improve listening comforts in background noise, digital noise reduction (DNR) systems are incorporated into hearing aids (HAs). Each hearing aid manufacturer has its proprietary algorithm for the DNR system. The amount of attenuation (dB) provided by the DNR system can be quantified using the hearing aid analyser. However, the standard test signals in the hearing aid analyser could not quantify the attenuation of DNR for speech mixed with noise signals. Therefore, this study aimed to (i) develop speech-plus-noise test signals that incorporate Malay sentences and (ii) quantify the efficacy of DNR systems in commercial hearing aids using the newly developed test signals. Six different brands of hearing aids with identical technology but from different manufacturers were subjected to electroacoustic testing utilising newly created Malay speech-in-noise test signals with and without DNR enabled. The total root-meansquare (RMS) gain reduction for each HA was calculated. The results show that the types of noise, the signal-to-noise ratio and the gender of the speaker have a significant effect (p<0.05) on the amount of gain reduction in the HA output as a result of the DNR system in each HA . In conclusion, the newly developed Malay speech-in-noise test signals can be used to verify the efficacy of DNR system in commercial hearing aids.