The surdo is one of the most important and characteristic instruments of samba in Rio de Janeiro, especially as a part of the drum groups in samba schools, where one can find anywhere from 25 to 35 surdos. They are large drums that mark the beat in samba music. They are low-pitched and are separated into in three different categories: surdos de primeira (first surdo), surdo de segunda (second surdo) and surdo de terceira (third surdo).
One of the main characteristics of samba is the low-pitched sound played on the second beat by the surdo de primeira. In most samba schools, this accentuated sound gets a response on the first beat with the higher-pitched, 55-inch rim surdo de segunda. Nonetheless, this call and response pattern is not a rule. At the Estação Primeira de Mangueira school, for example, the drum group is characterized by the absence of a response from the surdo on the first beat.
The surdo de terceira, on the other, has a 40-inch diameter and is the most high-pitched. It plays a number of syncopated rhythms that fill in the regular beat of the other drums.
In samba-reggae in Bahia, on the other hand, this instrument appears as a trio with a few differences: the third surdo is played with two drumsticks, while the others play inverted roles (the first surdo plays the first beat and the second plays the second beat).