Tinnitus is the sensation of hearing a sound, such as aringing or roaring, that does not come from your surroundings (nobody elsecan hear it). The sound may be continuous or intermittent, or it may keeptime with your heartbeat. To the person affected with tinnitus, the soundseems to come from one ear or from somewhere in the head. In rare cases, clickingor crackling sounds in the ear can be heard by the doctor as well as by theperson with tinnitus.

Normal sounds that come from your surroundings are "heard"when sound waves strike the eardrum. The eardrum vibrates, and those vibrationsenter the inner ear, where they stimulate nerve cells to create signals thattravel along the acoustic nerve to the brain. The brain then translates thesignals into patterns that you recognize as sounds.

Tinnitus occurs when there is no external source of soundwaves. For reasons that are not understood, the brain receives signals, eitherfrom inside the head or from within the ear, that cause the sensation of hearinga sound.

Tinnitus is most noticeable (and bothersome) when the affectedperson is in a quiet environment. The condition is often treated by usingbackground noise to mask the ringing or roaring caused by tinnitus.