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Modulation-Based Digital Noise Reduction for Application to Hearing Protectors to Reduce Noise and Maintain Intelligibility

Northern Illinois University, DeKalb, Illinois, kchung{at}niu.edu

Jennifer Tufts

University of Connecticut, Storrs, Connecticut

Lance Nelson

Purdue University, West Lafayette, Indiana

Objective: The objective of this study was to test the effects of modulation-based digital noise reduction (MB-DNR) on noise levels, speech intelligibility, and listening preference in four real-world noises. Background: A significant challenge in hearing protection device (HPD) design is to reduce ambient noise levels while maintaining users' ability to understand speech. MB-DNR technology, currently employed in hearing aids, potentially could be used to achieve these objectives. Methods: Speech and noise calibrated to signal-to-noise ratios (SNRs) of 0, —5, and —10 dB in the sound field were recorded at the outputs of two digital hearing aids in the ears of a Knowles Electronic Manikin for Acoustic Research with and without MB-DNR activated (i.e., NR and noNR, respectively). Listeners' speech intelligibility scores and sound quality preferences were evaluated while they listened to the recordings presented via ER-3A insert earphones at 85 dB SPL. Results: MB-DNR reduced the overall noise level by approximately 4 to 7 dB. Listeners obtained significantly higher speech intelligibility scores in the NR condition at an SNR of —10 dB in two noises and similar scores in the noNR and NR conditions in all other cases. They preferred the NR condition in all cases. Conclusion: MB-DNR reduced overall noise level, enhanced sound quality, and maintained or improved speech intelligibility in the four military noises tested. Applications: MB-DNR algorithms potentially could be incorporated into HPDs to enhance performance and increase user acceptance.

Key Words: modulation-based noise reduction • DNR • hearing protector • hearing aid • military noise • speech intelligibility • sound quality • speech prodcution and recognition • audition • sensory and perceptual processes • health and medical systems

Human Factors: The Journal of the Human Factors and Ergonomics Society, Vol. 51, No. 1, 78-89 (2009)
DOI: 10.1177/0018720809333083


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