Abstract: Electrical signal mixing apparatus for recording studio or live performance comprising a plurality of input channels having means for conditioning input signals applied thereto, a plurality of sub-group channels to which the signals from input channels can be selectively assigned, and a pair of output channels which may receive signals directly from the input channels or via the sub-group channels. Routing interconnections between the input, sub-group and output channels are controlled by a microprocessor in dependence on operator selections effected via a single manually operable switch control on each channel. The microprocessor detects destination assignments indicated by operation of the switch on a sub-group or output channel, and act to complete analogue interconnections between input channels and the identified sub-group or output channels upon subsequent actuation of the input channel selector switches.