The caixa and the tarol are membranophone instruments, also known to drummers as snare drums.
They have a cylindrical structure with two heads (usually made of plastic) attached and tensioned by metal rims. When the upper head is hit with two wooden drumsticks, small springs located in a metal mat vibrate and come into contact with the bottom head, producing the ringing sound often heard in military bands.
In samba, the caixa plays an important role, which is to provide basic rhythmic support, as it is the most rhythmically constant instrument in the group; this task is anything but simple.
The tarol, frequently mistaken for the caixa, is also responsible for maintaining the bases, or "laying the groundwork", but it is smaller and has a few key differences, such as a greater number of musical phrases and greater musical complexity. Considered a thing of the past, thetarol fights for a place in samba school drum groups, but samba mestres (masters) contend that the use of both the caixa and the tarol together would give the real identity to each drum group.