Self-Organized Criticality was initially proposed in 1987 as a general framework for understanding many instances of 1/f noise.

In the SOC paradigm, a myriad of independent systems related to one another by short range forces naturally organize themselves to a critical state defined by naturally occurring external condi- tions. At the critical state, these systems become complex and simple determinism is lost. The same minute perturbations can cause catastrophic changes or no change at all. However, the ma- jority of events would be small and over time the probability P (s) of events of size s would follow the power-law

P(f) = P0s??,(2)

where ? = 1.5 is the power law exponent of universal quality. The current experiment sonifies the mass of a bead pile driven to a critical state by dropping single beads onto the apex at discrete time intervals. An example of the mass a driven bead pile over time is displayed in Fig. 1. Though the mass over time does not explicitly display a distribution consistent with (1), the size of the resulting avalanches over time is within the upper limit of ?. The ideal avalanche size distribution is displayed in Fig. 2. A log-log plot reveals a straight line of slope -1.5. This behavior is exemplar

of SOC.


1=f noise describes the behavior of many naturally occurring complex dynamical systems over time. Perhaps more surprising than its ubiquity in nature is its prevalence in speech and especially music. Current research suggests that aspects of the human emotional response to music can be predicted using analysis based upon 1=f distributions. Musical compositions in which the pitch and duration of notes over time correspond to 1=f distributions have been found to be more pleasant than non-1=f distributions. The current research compares the sonification of a driven bead pile to an experimentally contrived deviation. Preliminary results suggest that the findings of pitch and duration may be extended to timbre and spatialization. The benefits of continued research into the application 1=f distributions in sonification for the auditory display community are discussed.