Darius Thieme explains:
"For example, let us consider some aspects of the Sango festival at Oyo. Firstly, the dates are set by a priest who practices Ifa divination.
Secondly, the musicians must be bata drummers, as this drum is sacred to Sango (the bata drum is conical, with two membranes, and has fixed pitches).
Special dancers come from the ranks of priests and initiates of theSango religion. A highly specialized kind of exhibition dancing must be performed, at times inducing a state of trance.
The dance requires rapid, angular, forceful body movement and is tightly synchronized with the master drummer's part: drummer and dancer work very closely together.
A highly stylized kind of singing is performed by Sango priestesses. A tense throat is used, and vocal tremolo embellishes the melodic line."(...)
"Speaking of the percussion music itself, bata drumming is perhaps more cohesively organized and more closely related to the emotions and symbolism of the event than anyother kind of Yoruba music.
The instrumental ensemble is very tightly organized. Two principal drums, the leader and assistant leader, share the function of imitating speech.
Their two parts are interdependent. Two small accompanying drums play interlocking parts in a rapid tempo, providing a constant, forceful background for the two lead instruments."
(Extracted from: Darius Thieme - Music in Yoruba Society.)
"The organization of the group of drummers is based on the strict and firm leadership role of the master drummer.
He signals rhythm changes, comments on the dance, and keeps the group together. Usually the leader is the best and most experienced drummer in the group.
The beginner or least experienced member will often be assigned a subordinate part; he may simply "double," or play the same rhythm as an elder brother in the ensemble.
The second best player may be assigned the part of assistant leader, with three or four additional accompanying drums included in the group."
(Extracted from: Thieme, Darius - Training and Musicianship among the Yoruba.)