It is often desirable to control musical objects or events in aggregates rather than individually. This might take the form of a series of events spaced in time, in which the details of the events follow from the larger arc (for instance, notes in a melody). Or the individuals might occur simultaneously, such as voices in a chord, or partials in a spectrum. In both cases the properties of the individual might be inferred from those of the whole.
A rich collection of tools and ideas has arisen in the electronic music repertory for describing individual behaviors from aggregate ones. In this chapter we cover two general classes of such tools: envelope generators and voice banks. The envelope generator automates behavior over time, and the voice bank over aggregates of simultaneous processes (such as signal generators.)