The bata drums are often described as musical accompaniment to Yoruba and Lucumi ceremony, and within the tradition they are nothing of the kind: they are the summons itself.
Speaking rhythms
The bata are a set of three double-headed, hourglass-shaped drums played as an ensemble to call the orisha. Each drum has two heads of different pitch, and the three interlock in speaking rhythms, each orisha having its own patterns. At a bembe or tambor the orisha are expected to arrive and to mount initiates to the sound of the drumming, so the drums do not accompany the event but produce it, which is a different relationship between instrument and rite than the word music implies.
The drum that is a spirit
A fully consecrated set, the drums with fundamento, is held to house the spirit Ana, the orisha of the drum, and playing such drums is itself a priestly office restricted to initiated drummers, the omo Ana. The first consecrated set in Cuba is traditionally credited to the drum-makers Atanda and Ana in the nineteenth century. The rhythms are among the most technically demanding in the Atlantic world and have passed into Cuban popular and art music, while consecrated performance remains bounded by ritual rule, so the same instrument leads a double life, one secular and one sacred.