An audio mixer is made up of three major sections. These three are your channel inputs, master section and level meters. A channel strip is a collection of controls, (coupled with an input jack) which your audio signal passes through before it reaches the speakers.
Common variables you will find in a channel strip include gain control, dynamic processing, filters, equalization, routing options and volume faders. Depending on your preference, most of these controls can be bypassed to utilize favored outboard gear. The master section typically houses any output EQ controls, built-in effects and sometimes the main output volume control (if the mixer is small enough to not have faders).
On some audio mixers you will find volume meters above the channel faders. This gives you an accurate visual on how hot your signal is. This is especially important in a studio where line and mic levels are a factor. Know how many mics you plan on using simultaneously, how much power you will need and which features are absolutely necessary when shopping for one to meet your needs.
Gain Control
The first knob you will encounter on a channel strip is always the gain control. This knob allows you to ensure the signal you’re working with is at a normal processing level. Many sound sources work at an input level far below an accepted processing level so a gain control allows you to boost the signal so it is workable. It also works to attenuate a signal that is too hot for processing. All of this is done by using the soundboard’s built in pre-amplifier. After the gain control, the signal passes through to dynamic processing.
Dynamic Processing
Dynamic processing is broken down into two categories: compressors and gates.
Compressor
A compressor is an electrical unit that attenuates high volume signals while boosting lower volume ones. Many soundboards come equipped with compressors either for each individual channel, a few individual channels, and/or one for the output. Compressors are very important to maintaining a reasonable even volume for the speakers and the listener. When looking for a mixer, you want as many compressors as you can get.
Gate
A gate is an electrical unit that cuts or dramatically decreases the volume of signals below a certain set threshold. Gates are extremely effective against microphone bleed and help clean up the sound. There are many affordable audio mixers out there that come with a gate control so make sure to check for this feature.
Filters & EQ
Filters and equalization are often coupled together because they both work directly with frequencies rather than volume.
Filters
A filter is an electronic unit that cuts out the extremities within the frequency spectrum. There are two types of filters; low end and high end. A low-end filter cuts out the lower frequencies and a high-end filter cuts out the higher ones. This coupled with gating can eliminate nearly if not all microphone bleed.
Equalizers
These are electrical units which can boost and cut certain frequencies anywhere across the spectrum. Equalizers come standard on every audio mixer. If you’re buying a soundboard without equalizers, take a deep breath and retrace your steps.
Amplifiers
A mixer in itself has no power and needs an amplifier. There are many mixers available now that come with an internal amplifier. There are pros and cons to both but the bottom line is that buying them separately is more expensive and more of a set up while buying them as one unit is more economic and less hassle.
Mixers are available from 300 to 1600 Watts which is considered consumer level. Depending on the size of your venue depends on how many watts you need. Generally if you’re serving a crowd of 250 people or less, you don’t need more than 700 watts. Mixers with over 1000 Watts of power are intended for larger audiences.