By Subong Kim, Ph.D.
Noise reduction (NR) is a common feature in modern hearing aids. You’d think it would be a universal win, helping everyone hear better in noisy places like restaurants or busy streets.
But that’s not what I hear from patients or see in the research. Some people love NR because it makes things feel calmer. Others hate it, saying the speech sounds weird or muffled.
As a hearing scientist, this puzzle intrigues me. Why does the same technology help some people but annoy others? I wanted to dig deeper and find a more objective way to predict who might benefit from NR—and who might not.
A big part of the problem is that most tests focus on behavior: asking people if they can understand words in noise, or how comfortable they feel. But these are influenced by many factors like mood, attention, or even how tired someone is. I wondered: Could we look directly at the brain’s response to NR-processed speech instead?
Not many studies have explored NR’s effect on brainstem measures—the early, automatic parts of our hearing pathway. The brainstem sits low in the brain, helping encode sound details like pitch and timing before sound signals travel higher up for conscious processing. If NR changes how the brainstem “hears” speech, that might explain why some people find NR helpful while others find it disruptive.
(A) Brain measurements of pitch response strength can predict how well someone will perform behaviorally when using noise reduction technology. (B) People who performed better with noise reduction showed different patterns of brain activity when processing speech frequencies compared with those who performed worse. Credit: Kim, Schroeder, Bharadwaj/Scientific Reports
In our study, whose results were published in Scientific Reports on July 1, 2025, we tested this idea by playing the syllable “da” for volunteers in three listening conditions: quiet, noise, and noise with NR applied. We recorded their brain activity from the scalp, capturing the brainstem’s responses to sound. We also measured how well people recognized words in noise, both with and without NR.
What we found was exciting. First, adding noise scrambled the brainstem’s response to speech. But with NR turned on, the brainstem’s response became clearer again for some people. We measured this in two ways: by checking how similar the responses were to quiet listening, and by analyzing how strongly the brainstem encoded the pitch (the “f0”) of the speech.
Even better, the strength of pitch encoding under NR was linked to how accurately people recognized words in noise. This suggests that measuring NR effects on subcortical speech encoding is doable, and could offer a novel way to predict who will benefit from NR in hearing aids.
I’m excited about where this could go. Imagine using brain tests to tailor hearing aid settings to each person’s unique auditory system. There’s more work ahead, especially to see how this applies to people with hearing loss. But for me, this study is an encouraging step toward solving the mystery of why some people love noise reduction—and others don’t.
A 2022–23 Emerging Research Grants scientist, Subong Kim, Ph.D., is an assistant professor of audiology in the department of communication sciences and disorders at Montclair State University in New Jersey. The study’s corresponding author is Hari Bharadwaj, Ph.D., a 2015 ERG scientist generously funded by Royal Arch Research Assistance.
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The strength of pitch encoding under noise reduction was linked to how accurately people recognized words in noise. This suggests that measuring NR effects on subcortical speech encoding is doable, and could offer a novel way to predict who will benefit from NR in hearing aids.