Abstract: An audio production console has a plurality of input modules connected between an input and a common output bus. The modules are identical, and contain a plurality of circuits for carrying out functions on a signal from the corresponding input. A central control unit is connected to each of the modules and controls selected circuits of the units, to control the operation of the module. In this way the functions carried out by the modules are freely selectable, and hence the switching of circuits within each module may be simplified. This enables the normal separate monitor section of an audio production console to be omitted from each module, simplifying the module and the operation of the console as a whole.