Abstract: Actuator apparatus for generating a physical effect, at least one attribute of which corresponds to at least one characteristic of a digital input signal sampled periodically in accordance with a sampling clock, the apparatus comprising at least one actuator device, each actuator device including an array of moving elements, wherein each individual moving element is operative to be constrained to travel alternately back and forth along a respective axis responsive to an individual first electrostatic force operative thereupon, wherein each moving element has an at-rest position and is driven away from its at rest position solely by the first electrostatic force; and at least one electrode operative to apply a controlled temporal sequence of potential differences with at least one individual moving element from among the array of moving elements thereby to selectably generate the first electrostatic force; and a controller operative to receive the digital input signal and to control at least one of the at leas