One definition of tinnitus, as compared to normal ear noise experience, is lasting five minutes at least twice a week. However, people with tinnitus often experience the noise more frequently than this. Tinnitus can be present constantly or intermittently. Some people with constant tinnitus might not be aware of it all the time, but only for example during the night when there is less environmental noise to mask it. Chronic tinnitus can be defined as tinnitus with duration of six months or more.