The ear and one’s perception of sound are very complex. Very simply put, we have the volume of sound, which is usually measured in decibels. And the frequency of sound, or the pitch. The high frequencies are more damaging to one’s hearing than the low ones. Therefore, most hearing protectors attenuate higher frequencies more than low ones.
More attenuation in the higher frequencies also has a disadvantage. The music doesn’t sound exactly the same as when you’re not using earplugs. Still, the difference is mainly audible to people who really listen to the music carefully. You hear the low tones a bit louder relative to the high ones. That’s why the Alpine PartyPlug Pro Natural earplugs have linear attenuation filters. They attenuate roughly the same amount of decibels over all frequencies. This causes a minimal distortion of the music. In other words: you hear the music in exactly the same way, but at a lower volume