Gain structure generally refers to setting proper input gain to achieve the best signal to noise ratio. Optimum gain is not just turning it up until it’s in the red as a lighting guy once told me! Hmmm.
Gain staging occurs at many places in the sound system- between the soundboard, signal processing, amplifiers, inside the soundboard itself, and from the various sources coming from the stage. The level coming into each piece of gear should be the same going out and the next device in the signal path should also be seeing the same level.
This is called ‘Unity Gain’. For example; if the output meter on your soundboard is showing 0dB (nominal) and the next device in the signal path is the system crossover, it should be seeing 0dB at the input and the signal leaving it should initially be 0dB, and so on down the line.
While some devices are used specifically to increase or decrease gain, and you may make adjustments to output levels to suit your needs, if you apply unity gain first, it will allow you to operate these properly.
Setting Optimal Gain of Your Inputs
The head amp or pre-amp is what you use to set your input gain on the soundboard. Each input channel will have its own dedicated gain control. When setting input gain on a channel, you should aim for nominal on the input or solo meter.
Nominal on analog is -0-, however on digital it can range from -12dB to -0- depending on the soundboard. On digital soundboards, it is generally the last green LED or just into the yellow. Red is clipping, and on analog it’s ok to find peak signals occasionally hitting the red. However, digital clipping sounds terrible and is something you want to avoid.
I personally used to love to drive my old analog Midas XL4 until it was just about to start tickling the red on the output meters. It really brought out the beautiful warmth of that desk, ah the good old days. But I would never dream of hitting any number of current digital desks that hard. As a matter of fact, I’ve heard several produce distortion well below ‘clipping’. Such a bummer.
Anyway, back to topic-there are several other gain stages in the path of an audio signal through the soundboard. The EQ, Inserts, Group Buses, Input Fader, and the Master Output Bus are all places where you can add or subtract gain to the input signal. However, it’s important to first set your head amp/pre-amp gain properly.
Without proper head amp or pre-amp gain on your input, your signals will be weak or distorted. If they are too weak, you’ll be trying to make up gain in other places, which can lead to added noise and potential feedback. Here’s a clue, if you are running all of your input faders all the way at the top to get enough volume, you probably need to adjust your input gain.
If the input gain on all or most of your channels is set too hot, it can cause the Stereo Mix to overload, producing that nasty distortion I was talking about earlier.
Start with optimal input gain on your input. When you begin with good sounds at the source and have set proper gain, you should be able to bring your input faders up to -0- and have the makings of a good mix. And if you’ve got a great band and great gear, even better!
The mix should fall together almost effortlessly.
Read more about live sound and mixing HERE
About the author- Michelle Sabolchick Pettinato has been a professional touring concert sound engineer for nearly 30 years and is currently FOH Engineer for Elvis Costello.