An apparatus for combining input signals produced by a plurality of electric musical devices includes a plurality of audio buses and a plurality of segments. Each segment includes input circuitry configured to receive at least one input signal from at least one electric musical device and to deliver the at least one input signal to one of the plurality of audio buses; a plurality of variable adjustment devices each associated with a corresponding one of the audio buses and each configured to change at least one property of an input signal received by another of the plurality of segments and carried on the corresponding one of the audio buses independent from input signals carried on other of the plurality of audio buses; and a mixer configured to combine the input signals carried on each of the plurality of audio buses into an output signal.