Gain Structure Overview
The concept of gain structure is controlling the amount of volume/power signals between components in the system. The objective is to get the signal level is as high as it can be, but no higher than the maximum level that your component allows. The result of to much gain is distortion, power lose , blown speakers, blown amps, hard to control sound , and feedback. Gain is power knob that increases amount of energy pulled from the amplifiers. When it increases power it increases volume or SPL. This is crucial when running a live set this is crucial.Passive systems
require amps to produce sound out of your speakers. Power plots are required to make sure enough amps or power are with your acquired speaker system. Each amp gets its own circuit to distribute power evenly without pulling to much power to trigger the circuit breaker. If your gain is to high it can result for an amp to trip a circuit breaker and turn off that circuit in mid performance therefore, losing speakers during show. If that happens run to your distro and reset that circuit breaker only. Knowing/labeling which speakers are on which circuit will save a lot of head ache. All pros use gain structure and power plots. They are the first key to being an audio technician/engineer.
Microphones are transducers that have opposite polarity of speakers that take in SPL rather than put out SPL. This diagram below, explains the dynamic range of a audio signal. At the bottom starts with no level and if you continue up to the next bar which is 0db(unison).
The signal in red is too high, and will cause it to clip or distort. To much Gain in a live setting is very serious when pulling power from a distro. The signal in yellow is too low and the lower signals in the audio are below the noise floor. The signal in green is the "sweet spot" some where between -12db to 0 db (unison) and represents the ideal audio signal level. A properly set up gain structure takes maximum advantage of the dynamic range to justify signal to noise ratio.
In a studio session poor gain structure effects DSP power or will have digital noise/artifacts. Most digital plugins are set to sound best or with minimal digital artifacts at input gain level at -12db of audio levels going in. Monitoring and watching SPL meters for tracks is a must. If your gain is in the "sweet spot" then plugins will respond better, therefore; resulting in a better sound. All plugins such as waves, UAD or any third party Plug in responds better when Audio signal is at -12db to 0db. Consistent gain structure makes it easy to make templates to speed up audio process in studio sessions.
There are two types of signal source checks, mic level check & line level check
First check if the microphone needs phantom power. If your microphone requires phantom power , then look for a button your channel strip that says 48+. When doing a mic check set faders at unison. When your fader is at 0 gently dial your gain knob to the "sweet spot" which is between -12 db and 0db of audio level. Gaining with faders at Unison helps you have the desired power/sound for the source. Having it at unison has more minute moves when moving volume fader up or down.
If you examine photo, unison to -5 or +5 is in increments of 1. Making it a more minute impact when moving faders. You can set gain to faders at -30 instead of unison but the result will be a drastic change in volume and makes it hard to control. If you look the distance between -40 to -60 are closer to each other. This is why the art of mixing to unison was created. It is design for the sound to be consistent across multiple audio output sources while also having minute ability to adjust faders.
How ever, Line checks must be done different.
Do not leave faders at unison when preforming a line check. Line sources have higher gain signal initially . Setting at 0 db can blow your speaker when the audio source begins. Set fader at -80 and slowly move up to hear volume. If the audio level is to high then use the (Pad) button on board channel strip or direct box. Pad reductions are usually -10 db to -20 db depending on your equipment.
Line sources are keyboards, auxiliary inputs(iPads), guitars and beat pads
If you have a line in instrument as a musician make sure you know your levels of your instrument. DJs understand you’re gain structure between songs so transitions won’t be to low but also so it won’t be to loud that it pushes limiters on systems.Gain & How It Effects Monitors
Gain structure is vital for the whole project as a whole. Make sure you have gain levels set at desirable levels before sending out to monitors or any aux outputs. If you turn down the gain mid performance then you are also turning down your gain across the board on all auxiliary mixes without touching the fader. If you turned down the guitar gain down then everyone on stage with a stage mix will ask for more guitar in their stage aux mix. Turning down gain on individual channels will carry over and turn down the level to aux sends. Your gain carries over across the board for each auxiliary output. This is important when you have multiple mixes going on and its important to have your primary mix set before sending it to other aux mixes.Checkout more about monitors and bussing here.