Etymotic HD-15 High-Definition electronic earplugs are designed to protect the hearing of anyone who operates around continuous loud noise. HD-15 earplugs allow users to hear naturally, as if nothing is in their ears. A dual-mode switch selects either automatic 15-dB protection or enhancement, which provides amplification for soft and conversational sounds when desired. Both modes block sudden, loud impact noise.. The HD-15 earplugs can be customized through the company’s CUSTOM-FIT program for personalized earmolds that provide a secure, comfortable fit. Provide a noise reduction rating (NRR) of 25 decibels.