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

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.