- Tinnitus etiology: All forms of tinnitus etiology will be accepted into Phase I providing they meet the following tinnitus criterion. Duration: 1 year or longer. Stability: Constant. Severity: > 50th percentile of OHSU Tinnitus Patients based upon Tinnitus Functional Index scores. Rated loudness: >6 on a 0-10 visual numerical scale. Tinnitus location: Unrestricted.