In Rio de Janeiro Carnival, the surdo is the large bass drum used in a samba school’s bateria.
The surdo produces the deep, resonant beats that anchor a samba ensemble’s pulse. Because it is played at a lower pitch than many other bateria instruments, it helps thousands of performers and spectators follow the parade’s rhythmic framework.
A bateria normally combines several percussion instruments rather than relying on one drum. Repiniques provide prominent calls and signals, tamborims add bright and rapid patterns, and agogôs contribute metallic tones. The surdo’s role is chiefly foundational and low-pitched.
The word bateria can mean the percussion section of a samba school. It should not be confused with the entire school or with the samba-enredo, which is the theme song performed during the parade.