The Surdo is a Brazilian bass drum and is usually played with one hand and a mallet. In a batería, there are at least three surdos, playing three different patterns. With their deep bass, surdos are used to keep time and form the backbone of the music. The first and biggest surdo is also known as the macasao. The varying tones of differing surdo sizes inject a melodious element to the bass line of the band.