Scheduling Algorithms for Real-time Sound Generation in Virtual Environments

Current tools for integrating spatial sound into Virtual Environment interfaces have not adequately addressed the problem of resource management in the sound generation process. Such systems place a hard limit on the number of sounds they support or in some cases they fail to maintain real-time evaluation rates when computational resources are exceeded. The research described in this dissertation addresses this problem. In order to establish a rigorous approach to resource management, a real-time scheduling strategy is employed. The sound generation process is expressed in terms of the hard real-time periodic job model and because the process is monotonic, the imprecise computation model is used. Three components are necessary in order to utilize the imprecise computation model: first an ordering scheme is established so that the active sounds in the environment can be rated according to their importance. Secondly, a method for iteratively evaluating sounds is devised. Finally a scheduling algorithm which minimizes the perceptible effects of degradation is established. The Least Utilization (LU) algorithm minimizes the average error given the characteristics of this problem. The behavior of the algorithm however produces perceptible discontinuities in the quality of the sounds during overload conditions. This behavior is quantified using a fairness index that was formulated. The scheduling algorithm must minimize both the average error and the fairness index. These two factors however are inversely related; reducing the fairness index raises the average error. The Priority Allocation (PA) algorithm developed in this research minimizes the fairness index while raising the average error somewhat. A listener study that was conducted in order to examine the effectiveness of these algorithms. It shows that under overload conditions, sounds generated using the PA algorithm were rated higher than those generated by the LU algorithm.