The mixer is basically the central command of any sound studio. You can do pretty much any thing in the studio without one, but when it comes time to bring everything together into a finished project a mixer is essential. The dazzling array of knobs, buttons, inputs, outputs and flashing lights is impressive, and somewhat off-putting to the uninitiated. In reality the mixer is just one channel repeated over and over again, with it's respective EQ/tone, volume, and pan controls. The function of the mixer is to combine several channels or input signals into one or more outputs.
Mixers, while they appear similar in nature, are designed for different functions, a studio mixer is designed for low noise, stage mixers are designed with a large number of outputs, and those used in the broadcast field offer cue functions and stereo faders, and other specialized functions indicative to that field. The most common way to refer to a mixer is by the number of inputs and outputs, such as 8 in, 2 out or 8X2, while some will have setups designating 8 inputs, 4 subgroups, and 2 outputs or 8X4X2. In the units having designated sub groups you would normally mix-down in two stages, doing a submix to a subgroup before finally mixing to stereo, this comes in handy with a large ensemble in which a brass, or percussion section could be mixed to a single subgroup.
General layout of a single channel, (strip), on a typical mixer.
Line or Mic input
XLR Input and 1/4" Input
The Low Cut button provides a steep drop off of low frequency noise. This frequency range is usually 75-80 Hz which eliminates room and air movement noise. It is commonly used in vocal EQ'ing.
The Gain knob allows the user to boost the level of the source to a typical line level. The gain is usually adjusted via a rotary trim potentiometer like the one pictured here. The gain knob is actually controlling the preamplifier in that channel, while some line level instruments may need little gain, a microphone might need a lot.
Auxiliary Sends allow each channel to send signals to an effects processor (reverb, delay, etc.) that have been patched into the appropriate auxiliary send, they are also commonly used for feeding a headphone mix during recording, or for feeding stage monitors for live performances. This mixer allows you to designate two sends to provide a separate mix for the performers. Sends that feed the inputs of effects are usually brought back into the mixer via the effects return section or into empty channel inputs.
The Equalization (or EQ) section is divided into three main frequency spectrums: low, mids, and highs. This gives you the ability to boost or cut a frequency or frequency range by a numbered amount of decibels. The "EQ In" button will activate or bypass the EQ section of that channel.
The Pan section of the mixer allows the user to place the sound source in the stereo field, from extreme left to extreme right in non-surround sound applications.
The Mute button allows you to quickly and easily mute whatever is on that channel.
The Solo button allows you to listen to one sound (or track) at a time. Sometimes it becomes necessary to single out a sound and listen to it separately in order to further adjust it. By punching solo on any given track all the remaining tracks are muted. Be careful when using this, on mixdown to tape you will ruin your recording.
The Fader is the volume control for the channel strip. It allows you to very easily and graphically see and change the mix.
Some mixers may also have buttons for individual buss assignments such as the one in the section pictured below.
The circuits in the mixer that actually combine the signals from the input modules is commonly referred to as a buss. Most mixers will have several busses providing a wide variety of features. The labeling of the busses may vary by manufacturer, but each buss works the same way electrically. If two busses are provided for a function, they are often labeled left and right. If there are more than two, they are numbered. The buss is like a parallel mixer allowing you to combine your inputs in a variety of ways.
Group/Buss Assignment Buttons allow you to direct the sound to whichever group output you desire. This allows you to group" together instruments. For example: group 1 & 2 (1 = left, 2 = right) could be all drum and percussion sounds; group 3 & 4 vocals; group 5 & 6 guitars, etc. While mixing you can quickly cut and boost entire instrument groups instead of having to do each one of them separately.
L/R Mix Button assigns the signal to the master left/right (L/R) section of the board. This is the easiest way to get signal to the outputs without having to group them to separate busses.
Typical Master Panel of a Mixer
Stereo AUX Returns of the mixer is where the effects processors are returned back into the inputs .Typically, these returns will have a solo button, a pot for level control, and pan pot for panning ability.
The Meter Section of any board allows you to visually see where your levels are at any given moment. On many boards you will see individual meters for each input channel as well as the stereo output meters pictured here, allowing you to see how much of each input signal is contributing to the final output.
These Faders control your main output levels that will be sent to tape. On many boards you will see additional group faders that are used to control individual subgroups and thus allowing greater control over the finished project.
So while mixers may seem excessively complex at first, when broken down into their individual sections and taken separately, we can see how these sections are used, and interact to come together as a complete tool for the studio engineer. You can purchase mixers with any number of inputs, the more inputs, the more complex the unit will appear but in essence the all generally work on the same principals, and when taken as individual sections won't seem quite so foreboding.
Typical Rear of a Mixer with inputs and outputs.
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