For hearing aid noise reduction, babble is not just babble
Most modern hearing aids provide single-microphone noise reduction without specifying how they work. The current study investigates how noise reduction is applied to babble noise in current premium hearing aids. Coupler gain measurements were performed in an acoustic test chamber. The signals used were standardized test signals, as well as babble noises compiled with different numbers of speakers (2, 4, 6, 8, and 10 speakers). The output of the hearing aid was measured with the noise reduction off and the strongest setting available. The gain reduction was calculated as the difference between the two settings. The results showed that, for an unmodulated test signal, the noise reduction algorithms applied quite different amounts of gain reduction across frequency. For the babble noise, some of the algorithms reduced gain very little, even for the 10-person babble. Other algorithms applied a graduated response, i.e., most gain reduction for 10-person babble, and the least amount of noise reduction for 2-person babble. Along with previous studies, this study highlights the need to have a standardized benchmarking procedure to define not only how noise reduction works in hearing aids but also which listening situations in which the noise reduction is active.
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