Musicians earplugs are acoustically tuned custom made plugs that were developed specifically for musicians.  The filters, inserted in the plugs,  attenuate the sound equally across all frequencies.  This enables the user to hear music more accurately but at a safer level.   The filters attenuate sound by 9, 15 or 25 dB and can be used interchangeably.  The ER filter is usually recommended as the first choice. 

H.E.A.R. (Hearing Education and Awareness for Rockers) is a non-profit volunteer organization dedicated to raising awareness of the real dangers of repeated exposure to excessive noise levels from music which can lead to permanent, and sometimes debilitating, hearing loss and tinnitus.