Noise-induced hearing loss. Damage to the cochlea, especially the outer hair cells, from prolonged exposure to sound above roughly 85 dB SPL or short exposure to anything much higher. It typically shows as a notch on the audiogram around 4 kHz. NIHL is permanent and the leading preventable cause of tinnitus worldwide. Custom-moulded musician earplugs and limiting concert exposure are the simplest defences.