A mixer, mixing board, or console sums multiple audio signals into one or more master outputs, and usually includes controls for adjusting the level and tone of each individual channel.
Types of Mixing Consoles
Mixers come in many shapes and sizes to suit a variety of tasks. They can be simple desktop boxes for mixing a handful of sources, medium-sized desks for live sound and small studios, or freestanding consoles with up to 128 channels and integrated patchbays. The majority of mixers are analog devices, but digital mixers are growing in popularity—especially for live sound.
Typical Layout
Mixers are typically comprised of a series of identical channels and a master section. Each channel takes the form of a vertical strip, with controls affecting the sound from top to bottom as signal flows through the unit to be combined with the other signals in the master section. Here are some common channel controls, in order of signal flow (top to bottom):
Input: Each channel has an input jack—typically, XLR microphone inputs or quarter-inch line inputs (often both, with a selector switch). A phantom power switch for powering condenser microphones is often included.
Gain or Trim control: Depending on the type of incoming signal, a microphone preamp or line-level trim knob coarsely boosts or attenuates the signal to the proper level for the mixer. A pad switch is also common, for attenuating very strong signals.
EQ section: For adjusting the tone and frequency content of each signal, most mixers include an assortment of low-pass, shelving, peak, and parametric equalizer knobs. The frequency and bandwidth options for each band can be fixed or sweepable.
Sends and routing: The send knobs and/or routing buttons allow signals to be sent to different outputs or groups. Sends are either pre-fader (for sending a separate mix to headphones or stage monitors) or post-fader (for submixing and sending a relative amount of signal to a group channel or effects device that will remain constant when the channel fader is moved).
Direct Outputs and Inserts: Located by the inputs, additional jacks are also common. Direct outputs allow post-EQ signals to be individually sent to a multitrack recorder, while insert jacks include a send and return on the same cable for easily patching in external processors on a single channel.
Pan Control: On stereo mixers, a pan knob controls how much signal is sent to the left and right channels of the main output, changing the perceived position of the sound. The default center position sends equal signal to the left and right.
Fader: Usually in the form of a linear potentiometer, the fader fine-tunes the final level of the signal being sent to the master output. The default position is unity (no boost or cut), increasing to +10db of gain and decreasing logarithmically to 0db.
Mute and Solo: A mute or off switch cuts the channel off from the master output, while a solo switch mutes all other channels, allowing the operator to hear a single sound alone temporarily.
While each of the channel strips contain the exact same controls, the master section has its own special set of features:
Group Channels: A smaller bank of mini-channels controls the overall levels of the group sends before they go to the master fader. Groups are used for adjusting sub-mixes like drum kits and backup singers, and may or may not have their own EQ sections.
Sends and Returns: The master section also contains master controls for headphone, monitor, and effects send outputs, as well as effect returns for mixing in the output of reverbs or other external processors.
Utilities: Some mixers include built-in talkback systems for communication, mono switches, dim switches, or “tape” outputs for recording the stereo mix.
Master Fader: Similar to the channel faders, the master fader controls the overall level sent to the main outputs. A mute switch is almost always included for emergency cutoff.