A sound mixer takes multiple audio signals and combines them into one or more output signals. It allows adjusting levels, adding effects, creating monitor feeds, and recording mixes. A mixer has input channels that receive audio sources. Each channel has controls for gain, equalization, auxiliary sends, panning, and level. Auxiliary sends route channel audio to other destinations like effects processors. Subgroups let channels be premixed before sending to the master output. The master fader controls the overall stereo output level. Mixers are used in music studios, television, live performances, and field recordings to combine and process multiple audio sources.