Four independent sample-and-hold circuits, plus a specialized logic circuit for expediently implementing polyphonic patches.
Sample-and-hold's are essentially one-cell analog memories. They are useful for "remembering" tine instantaneous value of a control voltage (a detected envelope, for example), for generating equally space steps from a constant slope input (as from a 280 Envelope Generator), and for converting any continuously changing voltage (a random voltage, for instance) into a series of discrete values.
The 264's sample-and-hold circuits have two operating modes: sample and track.
In the sample mode, the value of the input is sampled and applied to the output whenever a pulse is received. The output remains at the value until the next pulse arrives. The track mode differs in that an input is applied to the output for the duration of the pulse. The output tracks the input until the end of the pulse and remains at a constant value until the next pulse. The Model 264 includes a polyphonic adaptor, which performs the logic necessary to implement four-voice polyphony. Facilities are incorporate for fine tuning and f.m. modulation the oscillator; light emitters display the adaptor's operation.