This study is ongoing, but not recruiting participants. Change in subjective Tinnitus after 4 weeks treatment [ Time Frame: 28 days ] [ Designated as safety issue: No ] To compare the change from baseline (D1 to D28) of the Tinnitus Functional Index overall score between AUT00063 (800 mg) and placebo. To further investigate the safety and tolerability profile of repeat administration of AUT00063 (assessing vital signs, physical examination, laboratory exams and ECG) [ Time Frame: 42 days ] [ Designated as safety issue: Yes ] To investigate the safety and tolerability of AUT00063 by assessing vital signs, physical examination,...