The orchestra’s three percussion instruments work in collaboration to create a single rhythmic pattern that provides the composition with a regular metric outline in support of the melody. It has its own internal hierarchy, where the shōkō functions to articulate the downbeat of every measure, and the kakko’s role is to control the accelerandos that lead to some selected downbeats. The function of the taiko is to articulate the most important downbeat of the entire phrase: its half-point called the obachi. As a matter of fact, obachi is the only beat where the three percussion instruments meet. Example 1 shows the basic rhythmic pattern used in the phrase structure of 4 measures with 4 pulsations per measure.
The taiko's part is easy, with only two attacks per cycle, and it is also difficult because the performer cannot afford loosing count, since one of the two attacks is the cycle’s most important one. Hence the performance of the taiko includes hand gestures that add a ceremonial tone to the performance and also help the performer keep up with counting. After the half-point attack, the player’s left arm makes a circular motion and brings his/her left hand to rest on his/her left thigh, at which point the right arm performs a similar gesture and brings his/her right hand to rest on his/her right thigh. Then the left hand gets in place to perform the mebachi followed by the right hand being ready to perform the obachi, at which point the arm patterns start over again.
Although the three percussion instruments are united in producing a single rhythmic pattern, their different functions and timbres prevent them from merging into a single sonority. As shown in Example 1, the two most active instruments are the shōkōkakko. The reason why their superposed sound remain clearly distinguishable is related to the fact that the former is an idiophone and the latter a membranophone, and because their sound occupies two separate areas on the frequency scale as demonstrated in Figure 1, which shows that the energetic pattern of shōkō’skakko's (in red) is located between 350-1100 Hz.
The different timbre of the percussion instruments helps articulate the phrase structure at three different speed levels. The first level of articulation is the fastest one, and it comes from the high and piercing attack of the shōkō, which usually marks off the downbeat of every measure. The second level of articulation is an intermediate one, and it comes from the kakko, whose roll emphasizes selected downbeats, usually one every two measures. Finally, the last level of articulation is the slowest one, and it comes from the taiko's obachi, which accentuates the most important downbeat of the entire cycle: its mid-point.
As demonstrated in the other chapters under 'Orchestration', timbral transformations and phrase structure go hand-in-hand. The macro rhythm created by the percussion instruments provides the listener with a temporal canvas against which one can appreciate the transformations of timbre in the other sections.