Premium electronic earplugs usually find their homes with musicians eager to preserve their hearing at all costs; anyone within the crowd has more often been left to either use cruder plugs or cover their ears. Etymotic wants to bridge that difference with the Musico.Pro 9-15. The combination of ER-9 and ER-15 earplugs matches its namesake not just through the choice of components, but through active noise cancellation that removes 9 to 15 decibels from the sound only when the rock gets too raucous: listeners can hear fellow