X0306 4 2021-02-17 0 0001656536 Decibel Therapeutics, Inc. DBTX 0001620014 Exter Neil C/O DECIBEL THERAPEUTICS, INC. 1325 BOYLSTON STREET, SUITE 500 BOSTON MA 02215 1 0 1 0 Common Stock 2021-02-17 4 C 0 2938945 A 2986114 I See footnote Common Stock 2021-02-17 4 C 0 98929 A 3085043 I See footnote Common Stock 2021-02-17 4 C 0 54642 A 3139685 I See footnote Series A Preferred Stock 2021-02-17 4 C 0 45638882 0.00 D Common Stock 2938945 0 I See footnote Series C Preferred Stock 2021-02-17 4 C 0 1250000 0.00 D Common Stock 98929 0 I See footnote Series D Preferred Stock 2021-02-17 4 C 0 289603 0.00 D Common Stock 54642 0 I See footnote On February 17, 2021, the Series A Preferred Stock automatically converted into Common Stock on a 15.529-for-one basis without payment of further consideration upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date. On February 17, 2021, the Series C Preferred Stock automatically converted into Common Stock on a 12.6352-for-one basis without payment of further consideration upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date. On February 17, 2021, the Series D Preferred Stock automatically converted into Common Stock on a 5.3-for-one basis without payment of further consideration upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date. Held of record by Third Rock Ventures III, L.P. ("TRV III"). The Reporting Person is a partner of Third Rock Ventures GP III, L.P., which is the general partner of TRV III. The Reporting Person disclaims beneficial ownership over such shares, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares. /s/ Ronald Vigliotta, Attorney-in-Fact 2021-02-19