Examples

Expressiveness in percussion instruments lies in the ability to excite or touch objects (haptic response), with other objects and in numerous ways [5, Verplank, 2000]. For this reason, system energy parameters, momentum and boundary conditions need to be part of the system. Therefore, intensity, energy amount, decaying times, damping and reverberation were taken as the momentum and likewise number of beans, probability of collision, shell frequency and shell resonance as the boundary conditions. The examples in figure (2) are clm instrument calls and illustrate all the above points.

Algorithm No. 1, is the simplest call in the composition. It is an answer and response phrase lasting one second each with 4 shakes per second. In algorithm No. 2, we have the same phrase with a new response by doubling the shake rate in the response, and by adding a triplet at the ending. Different amplitude values give values for up and down beats. Notice that by manipulating either decay times or probabilities of collision of seeds, we get timbres such as the cabasa but with the shake (dynamics) of the maraca. In algorithm No. 3, we get the sound of a wind chime by inhibiting low-pass filters in the model. Algorithm No.4, is a full maraca ensemble with a 28 measure syncopated rhythm movings across the sound space.Notice that different amplitudes give downbeats, envelopes for time changing shell frequency which might be the effect of the muscles of a real performer and different maracas.

Figure 2: Algorithmic Examples