Outside of going to a doctor, it isn't always easy to detemine whether you've damaged your hearing. But if sounds seem muffled, or you notice a ringing in your ears after noise exposure, this is a pretty good sign that you haven't done your hearing any favors. You may be experiencing what experts call "a temporary threshold shift" of your hearing. Keep exposing yourself to loud noises long enough, and the temporary shift could become a permanent hearing loss. 8 hours at 85 decibels is OSHA's measure.