What does a Mixer do?

No matter how sophisticated or expensive, all mixers carry
out the same basic function - to blend and control the
volume of a number of input signals, add effects and
processing where required and route the resulting mix to
the appropriate destination, which could be power
amplifiers, the tracks of a recording device - or both. A
mixer is the nerve centre of these sources, and therefore the
most vital part of your audio system.