Gain Staging - the Missing key to a great mix
A good portion of my time at VIP is spent in consultation and training with churches and schools. Installing new equipment often gives me the opportunity to observe the methods and procedures technicians use during sound check and for mixing, and I see it all, from the novice to the experienced user.
Without a doubt, the number one issue I find in venues is a lack of understanding of proper speaker placement (See my previous blog for more information: click here), but the second most common issue is a lack of understanding of gain staging and why it’s important. It’s the bedrock of a good mix and a critical component to avoiding a couple of other common issues.
The purpose of a sound reinforcement system is to make quiet things louder. We take a variety of audio sources that need to be heard—vocal mics, keyboards, drums, guitars, speaking mics—and increase their volume in a space so that everyone in it can hear clearly. At least that’s the goal. In my audio classes I teach that the sign of a job well done is that no one notices the sound system. When we eliminate distractions like buzz, hiss, popping, shrill vocals and instruments out of balance, the sound system will “disappear”, allowing the audience to focus on the material being presented.
The process of amplifying all those sources happens in stages. At the instrument level, we have pre-amplifiers and processors in guitar pedals, volume controls on keyboards, sensitivity adjustments in microphones and amplifiers in guitar pickups and condenser mics; down the chain we use pre-amplifiers in stage boxes and mixing consoles; in old analog consoles, we had summing amplifiers on busses, which are mostly eliminated now with digital mixing; at the output, there’s amplification and reduction of bands of frequencies in digital signal processing with equalization and crossover functions and finally the biggest increase in signal level with power amplifiers. Over-amplifying or under-amplifying at any of these stages can cause noise that makes your sound system get noticed.
All audio signals contain a percentage of noise of some sort called the noise floor. If you turn a quiet channel way up, often you’ll hear the noise as a hiss or buzzing that is always there in the background but usually undetectable, as it is quieter than the signal. Signal-to-noise ratio is a measurement of the difference in loudness between the noise floor and the desirable portion of the signal. The goal in sound reinforcement is to get a high signal-to-noise ratio early in the signal chain so that subsequent amplification doesn’t over-amplify the noise along with the signal, making it noticeable.
If you have hiss in your system, you are very likely over-amplifying background noise. Start by getting as much signal as you can from the source. I generally tell my instrumentalists on stage to give me at least 80% of max volume at their outputs. If you have to excessively crank the head amp gain to get the signal level you want, it’s worth the time it takes to fix the real issue in the signal source instead.
The other issue that pops up with improper gain staging is distortion. Over-amplifying a signal at one stage may result in over-driving the input of the next. When a signal is too hot for an input to take, the waveform is clipped where it exceeds the capacity of the electronics, resulting in distortion. In the illustration, you can see that the tops and bottoms of the original waveform, represented by the dashed lines, are “clipped” off. Another word for distortion is clipping.
When you hear distortion, look at what is overdriving and reduce the prior amplification stage to decrease the input signal to the section that is clipping. It might be a head amp that needs a pad applied, or a hot instrument on stage that needs to turn down, or insufficient amplification in the power amplifiers that won’t get loud enough to keep up with the engineer who’s driving the faders to the top.
As a side note, you’ll want to fix clipping/distortion as soon as possible because it’s really hard on speakers. Even if the distortion is not happening at the power amplifier, it pushes the speaker diaphragm to the limits of its extrusion length, as the signal path in the illustration suggests, and holds it there for a relatively long period of time. That builds heat in the coils and reduces the airflow that would help cool them, which drastically reduces the life of the speaker.
Head amp gain is so important that when I do sound checks for the festivals/bands I’m mixing, I use the following procedure for each channel in the mix so that I get the head amp gain set correctly. This is also the basic procedure I teach in my classes:
Turn the channel gain and monitor sends down so as not to blast the band from the previous settings (as needed). I usually make sure there’s a little of the channel in the monitor mix for the person that is performing so they can hear it working. That tends to eliminate the fumbling for the switch on a wireless device or the plugging and unplugging of cables when the guitar fails to make noise immediately.
Make sure I can see the input level on a meter, which may require hitting a PFL or Solo button for some mixers.
Turn the channel on.
Ask the performer to play or sing at their maximum program level, which is not to be confused with “as loud as they can”. For acoustic guitar players, this means strumming, not picking. For vocalists, it means the chorus of the fast song, not the intro to the ballad or simply saying, “Check, check, that’s good.” I often ask drummers, “Is that how hard you’re going to hit that?”
Bring the gain up until the metering shows their signal averaging around the nominal level on the meter. On an analog meter, that’s the zero, but on digital ones, it’s usually where the leds change from green to yellow. Check your console’s manual if you’re not sure where nominal is.
Do a quick, basic EQ to get the sound close to where it’ll be for the performance and re-check the level. A drastic EQ can change the gain required at the head amp, so it’s important to get the big changes done now and leave the finesse until later.
Bring up the monitor levels in each monitor mix to where each performer wants it.
The reason we don’t take the gain to the top of the meter in step 5 is to leave some headroom on the channel, which can help prevent distortion. Sometimes musicians will play louder with the nerves of a performance than they do in rehearsal. Headroom gives us enough space to vary on the loud side without hitting the top of what the channel can take, causing distortion.
This looks like a long process, but with practice it can go fairly quickly. I have been known to move through sound check in under 15 minutes with a full band, including drums and monitor mixes. The way gain staging affects the rest of the mix makes it imperative that you take enough time to do it correctly.
The next place gains get messed up is in the faders. I can’t tell you how many times I’ve seen mixing with all the channel faders near the top of their run and the master fader down close to the bottom. I’ve also seen the reverse. The cleanest possible sound you can get through a console is one in which the processing, including amplification and gain reduction is at a minimum. That’s what the nominal setting, or “0” on the faders is for. When everything passes through at nominal, the signal is changed as little as possible. Balance out your faders.
This can also be affected by the next stage. If your sound system is too powerful for your audience, it’s a common practice to pull the master fader down to keep the volume where you want it. It’s ok to do that once-in-a-while, but if you’re running that way consistently, you’re over-amplifying at the power amps. It’s better to turn down the amplifiers so you can run all the faders near nominal, including the master. This takes a little work, and a knowledge of what your maximum volume should be, but doing so makes for a much cleaner mix. If you have a constant hiss in your speakers, you may be over-amplifying at the power amps.
Here are a few other places where improper gain staging can affect the quality of your signal:
Between the transmitter and receiver in an analog wireless system, both microphones and in-ear monitors
Between connections in guitar pedals
Drastic EQs where the resulting curve just turns the whole signal down or up, on channels or on outputs (31 band graphic)
Monitor mixing, same as above with fader imbalances
Over-powered or under-powered monitor cabinets
Clean up the imbalances in gain staging, and you’ll likely notice that you have a much cleaner, easier to manage mix. If you want more information or another set of ears to help you, contact VIP Production Northwest to have an audio consultant come help you take an in-depth look at your system.
