The Mystery of Gain Staging

One of the hot topics at this year’s NAMM show was gain staging. Lots of people want to know what it is and why you need to know how to do it. It’s also the root of some of the more common mistakes I see in many churches and schools. It’s not intuitive, but knowing how to do it makes a world of difference in your signal quality.

What is gain staging? It’s the process by which we get the appropriate amount of amplification (gain) from each leg of the signal chain from instrument to speaker. There are amplifiers everywhere in pro audio, starting with the output of instruments like keyboards and guitars, including head amp, EQ, dynamics and mix bus faders on consoles, and in digital signal processing and the amplifiers that drive the speakers. Proper gain staging balances out all of those stages of amplification.

Why is gain staging important? Analog audio signals exist as alternating currents moving through wires and components. The loudness of those signals is represented by the voltage. Higher voltages represent louder signals, so amplifying them increases the voltage. If the signal is amplified to the point that it has higher voltages than the device it’s feeding can handle, the waveform gets clipped off or flattened, which causes distortion. Over-amplifying any leg of the signal can cause distortion, even in a signal in a digital console.

On the other end of that spectrum, if a signal is too weak to begin with, then it will require lots of amplification in subsequent legs of the signal chain, which will also amplify the background noise in the signal. Every signal has background noise in it from electronic components or even the environment in which the signal is captured. Over-amplifying background noise comes out of the speakers as hiss; it’s essentially white noise. Getting enough signal early in the chain helps to avoid hiss.

In old analog consoles, we used to run our faders as close to the “Nominal” or zero point as possible. This is because it was the sweet spot on the fader–the point at which we were not amplifying or attenuating the signal. Any time you modify a signal, by amplification or attenuation, including modifying just a band of frequencies with EQ, you lose some of the original quality of that signal, even with digital processing. 

When you’re getting ready to set your channel gain (head amp) during sound check, start with a strong signal. I ask keyboard players to run their output at 80% or higher. I ask acoustic guitar players to do the same. There is a sweet spot for each instrument, and it will vary, so play with it as time permits. The goal is to get a big amplitude difference between the clean signal and the noise floor from the very beginning without overdriving or using up headroom. Also, pay attention to the “hidden” signal issues, like the pad button on the keyboard’s DI. Only engage that if the signal is too hot for your console.

Different consoles have different meters that show how much signal is coming through the preamp or head amp. When we’re setting the head amp gain, we’re going for a nominal amount of signal–usually strong enough to tickle the yellow, giving us a strong signal, but leaving enough headroom to handle the increase in volume when a performer gets into the performance. Worship artists are notorious for giving you their “max” level during rehearsal and then adding another 6dB when they get into the worship set. Plan accordingly.

During sound check, I ask the musicians to play or sing at the loudest level they will hit during their set. Note that I didn’t write “as loud as you can” but we want to avoid the drummer that barely taps the floor tom in sound check, then gets into it during the performance and beats out a 20dB increase in level. We also don’t want the vocalists to whisper, “Check, check,” in sound check. We want them belting the biggest chorus to their favorite song. Then I set their head amp gain with that signal as my reference.

My favorite sound check ever was a national band’s lead singer who understood the assignment. When I asked him to check his mic, he put it right up to his lips and said, “Check one, TWO!! One, TWO!!” and on the two, he practically yelled into the microphone, followed with, “That’s about how loud I’ll be during the set.” Someone somewhere taught him the importance of gain and it stuck!

I know what you’re thinking: “If I crank the gain up that loud, they’ll be blasting in my house mix and I’ll have to run all the faders way down.” Don’t worry; we’ll address that in a minute, and yes, it’s still about gain staging. 

Set the head amp gain appropriately for each channel and then don’t touch it again…unless you have to. The gain determines how much signal is going to all the places it has to go, including monitors. If you change the gain, it also changes the amount of that channel going into the performers’ ears–all of them–and other things like broadcast or foyer sends. Only change the gain if you have to, such as when it’s distorting, and make sure you let them know that you’re doing it–usually at a break between songs–so they can adjust.

A note on EQ: With modern digital mixing consoles, we have a number of parametric EQ bands available to us. The temptation is to go hog wild with those and use wide filters to make sweeping changes in the EQ. Sometimes a wide filter is appropriate, like when you want to “flavor” the channel with increased warmth or crispness. However, if all your filters are making wide cuts in the frequency spectrum, leaving nothing above the zero line, then all you’re doing is turning the volume down with the wrong tool. Every time you make changes with EQ, it “dirties” the sound a bit with the way those bands interact with each other.

Using the EQ to turn the signal down just messes with the signal more than simply turning it down with the fader. If you’re “fixing” feedback, find the exact frequency that is troublesome and notch it with a narrow filter. The EQ in the picture may fix the feedback, but it’s actually worse than just turning it down 3dB.

The next leg of gain–mix buses (aux sends, effects and mains)--is another common problem area. If your channel faders or monitor sends are low and your main output fader/knob is high, then it’s not balanced and you run the risk of overdriving an input/output. Your output should be at nominal and main mix components at or below nominal. Also, watch the volume on packs for your in-ear systems. It’s common to overdrive the input of the IEM by cranking the channels up, instead of turning the volume at the pack.

Alternatively, if your channel faders are at the top or in the nominal range, but your master fader is below nominal, then you’re likely amplifying noise in your main speakers. If you bring up your gain so that you have to bring down the main fader to keep it at a reasonable level, which is a common problem, I’m talking to you. Here’s a good method for fixing that: turn your amplifier(s) down, run music through a channel with the fader at nominal, and run your main fader up to nominal so that you get a good signal on your main output meters. Then turn the amplifiers back up until you reach the level you usually run in your room (use your dB meter). That gives you plenty of headroom without over-amplifying your noise floor. 

There are more stages of gain in a system than I can cover in what was supposed to be a short article. However, knowing why and how to get an appropriate amount of gain out of each will hopefully help you think through the process and result in a markedly cleaner signal.