Mixers are available in a great deal of formats and sizes, and even though most share the same fundamentals, there are many variants and options to choose from. As a mixer will probably be one of the largest single purchases you'll make for your set-up, it's particularly important to know your exact requirements before buying.
Historically, mixers were designed specifically for use in either a live or a studio setting, whereas these days, particularly at the low to mid-end of the market, the flexibility incorporated into their designs means that the same mixer can often be put to good use in either environment. Whether you are intending to use your mixer in a studio, or as a front of house (FOH) or monitor mixer, you should always consider the different scenarios you may encounter in the future. Limited numbers of inputs, outputs and auxiliary sends are the most common shortcomings of mixers, so it's a good idea to have a few extra as you'll often find yourself needing them at a later date.
Although even the most basic mixers can appear daunting to the uninitiated, once you understand a single input channel and the main output section, you're pretty much there - ultimately, everything can broken down into either inputs or outputs. The input section of the mixer will typically have microphone inputs on balanced XLR connectors, unbalanced line inputs on jack connectors, or often a combination of both. Each input channel will have a selection of signal processing controls such as gain, EQ, pan and auxiliary or 'aux'h sends. The output section groups all the inputs together ready for any final processing, before being sent to the main stereo output. In some cases you will find 'groups' or 'buses' where a collection of individual channels can be grouped together to form a sub-mix, allowing them all to be controlled by a single fader, before the group's own output is routed to the master section. We'll look at each of these functions more closely in the 'features' section.