It is often desirable to control musical objects or events as aggregates rather than individually. Aggregates 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 sound simultaneously, as with voices in a chord, or partials in a complex tone. Often some or all properties of the individual elements are best 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).