A method of manufacturing an Active Noise Reduction (ANR) device includes providing at a stage during manufacture a pre-completion ANR device in a non-final configuration, the pre-completion ANR device including a plurality of inputs, a plurality of signal processing resources, an output for driving an earphone driver, and a programmable switch arrangement capable of assigning any of the plurality of inputs to any of the plurality of signal processing resources, selecting from the plurality of signal processing resources a subset of signal processing resources to contribute to the output, whereby the remaining signal processing resources of the plurality do not contribute to the output in any mode of operation of the ANR device, and in a configuration step during manufacture, programming the programmable switch arrangement to assign each of at least a subset of the plurality of inputs to a different one of the selected subset of signal processing resources.