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The moment your church decides to install or improve its sound system, the search for the right mixer becomes a priority. In this article we'll explore what a mixer does and how to select one based on the style of your worship service.

Basically, a mixer, sometimes referred to as a console, combines all of the audio sources in a sound system into something workable. You simply can't take three or four microphones and wire them all into the same jack on an amplifier. The signal would be too low, and the microphones would conflict electronically with each other. But, using a mixer, you can amplify each input as much as needed—through an adjustable gain—and then combine them through a summing amplifier. Each source, whether a microphone or a cassette, vcr, or cd, needs adjustable levels, so the sound from one of them won't overwhelm other signals. The console also routes these combined signals to different destinations, including amplifiers, equalizers, and recording systems. This entire process is referred to as mixing.

The structure of a mixing console starts with an input. Typically that input will have an xlr connector for microphones, a trs connector (for tip, ring, sleeve, like that found on a stereo headphone) for line-level sources or some other style connector for bringing in both balanced and unbalanced signals. The input feed goes first to a preamplier, or preamp. This is a low-noise amplifier circuit that will increase the level of the signal from a microphone from thousandths of a volt to about one volt. The control for this preamp is labeled gain, input trim, or some other similar name. It is almost always the first knob at the top of the board. If this critical control is turned up too high, the level becomes too strong for the circuit limits and clipping (distortion) can occur. If it is turned too low, other parts of the sound system will have to be turned up to compensate, and there will be too much noise in the system. The input gain has more impact on the signal to noise ratio in a sound system than virtually any other component.

After the preamp, the signal is then passed on to one or more mixing busses. The bus is where the signals from other inputs are combined. Each bus is sent to a different output on the board. In some cases, users will find a fader on the way to one or more of these busses. The fader is either a rotary knob or a linear control (called a fader or slider) that allows users to adjust the level to the mix without adversely affecting the input trim. The fader is a passive device, so it will not change the signal to noise ratio of your system. Users can change the audio on a particular channel without causing more noise or distortion.

After the signals are all combined on the bus and each adjusted by its own fader, the combined signal will pass though another amplifier circuit called a summing amp. These faders adjust the final output level of the mixer and the sound system levels. A mixer is described by the number of inputs and the number of busses that lead to outputs. A 4 x 2 mixer has 4 input channels and 2 outputs. A 32 x 8 board has 32 inputs and 8 outputs.

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