An Auxiliary Channel on a mixer is a separate audio bus (mix) that can be used to send audio out of different outputs on a mixer. For example, an auxiliary channel can be used to send audio to musicians for foldback or to a recording device or to an effects processor. An Auxiliary Send is a knob on a mixer channel to 'send' audio to a particular auxiliary channel. An auxiliary return is a separate input on a mixer that can be routed to main mix.