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Demystified

sound board

It’s a long running joke in the live sound business that at nearly any show, some audience member will come up to the console and ask, “Wow, do you really know what all those knobs and buttons do?!” It’s an understandable question—with so many things to turn and tweak, a sound console can appear pretty scary to the newcomer. One of the most frightening sections for somebody who hasn’t used one before is the equalizer, or EQ—those knobs on each input channel that say “high,” “high mid,” “low mid,” and “low,” and the other buttons and knobs that go with them.

They’re really not as complicated as they seem, when you break them down to the basics, which is exactly what we’re going to do in this article. EQ is a way of controlling the tone of the sound you’re listening to. If you’ve ever adjusted the bass or treble settings on a home or car stereo, you’ve used a very simple EQ section.

There are two places EQ is generally used in live sound. The first is on the outputs of a sound system, where it’s used to adjust how the speakers sound (both in and of themselves, and how they interact with the shape and construction of the room) in order to make things sound nice and even, and to eliminate most nasty feedback howls and squeals. The second place is on the input channels—the vocals and instruments—in order to adjust the tone of these sound sources and make them sound natural and blend well together.

In this article, we’re only going to deal with the second type of EQ. The first type can make or break a sound system, and is something that’s best left for people with lots of experience doing sound, and often with specialized (and expensive!) measurement hardware and software. If your school’s sound system has a password locking you out of a processor or a security cover over a piece of equipment, odds are that’s the “magic box” that’s doing the systemwide EQ, and it’s covered because it doesn’t need to change. Messing with it could prove disastrous to how the system sounds.

There’s a trick to it…

So, how can we learn to EQ a singer or instrument easily? First, let’s break that EQ section down into its parts. Each channel of your board will have four, or in some cases three, copies of the same set of knobs, each covering a different frequency range. There’s low (this is kind of like the bass knob on your stereo), which covers the sounds that go boom and thud. Then there are the mids, which on many higher end consoles are broken into low-mids and high-mids; this is where the real meat of a sound often is. The important parts of the human voice are in the mids, as well as the fullness of drums and in fact most other instruments. Finally, there are the highs, where all the pop and sizzle is. This is where you’ll find the crispness of t and p and s sounds, and the cymbals on a drum set are almost all high frequencies.

To give you an idea of where different instruments fall in the frequency range, the chart on the facing page shows the tonal ranges of some common instruments with both the actual frequencies (which are measured in hertz, something music and physics teachers would be thrilled to explain in lots of detail) and the corresponding notes on a piano keyboard, which, short of a pipe organ, is the widest-ranging instrument you’re likely to come across.

You can, for now, ignore the actual frequency numbers. Eventually you should learn how these frequencies sound so you can communicate with other sound engineers and more quickly dial in the sound you want. For the time being, I’m going to show you a trick that will make it easy to learn to get the sound you want without worrying about those numbers. Let’s not get ahead of ourselves, though—first let’s see what these knobs do.

Each frequency range in a sweepable EQ circuit is controlled by two key knobs, one labeled “frequency” and one that says “level” or “gain.” (On some boards the frequency knob will be labeled kHz, for kilohertz, or in the case of the low range knob, Hz, for hertz. The gain or level knob may be labeled dB.) The frequency knob selects the frequency of the input you’re going to adjust; the level knob actually does the work of boosting or pulling back that part of the sound. Some consoles lack a dedicated frequency control for the EQ. In this case you can still identify and fix problems but you will be limited in your ability to fine-tune those frequencies.

Take a look at the level knob. You’ll note that the 0 setting is in the middle, and you can turn this knob in either direction: clockwise to boost the gain, counter-clockwise to turn it down. It’s a longstanding rule of sound that, whenever possible, you should turn the level down, not up. This usually produces a more natural sound. Boosting the EQ too much can quickly dig you into a hole in terms of both tone and potential for feedback.

Finally, on most higher end consoles, there’s a third knob, called “bandwidth” or “Q.” Some consoles will make do with just a button that switches between two settings for this, instead of a full knob. This control tells the console how wide a range of frequencies to change when you turn the level knob. It can change anything from a really narrow slice of just a few frequencies (this is often used to take care of feedback), to a really wide chunk all at once. Some consoles won’t have this knob at all, or will only have it for the mid frequencies, and not the highs or lows.

Frequency ranges of various musical instruments and the human voice.

And here’s what it is

So, about that trick I mentioned: let’s assume we’ve got an instrument playing through the sound system, and it just doesn’t sound quite right. We’ll also assume that the instrument is properly tuned, and the musician is properly trained, to make our lives easier—if the musician isn’t good or the instrument doesn’t sound good on its own, we can turn knobs all day long and it still won’t sound any better.

With experience, you’ll learn how to tell almost automatically what frequencies to turn down to make an instrument sound the way you want it. Until you’ve acquired that skill, stop and listen, and try to narrow down what part sounds off. What part of the sound are you hearing too much of? Is it the lows, the mids, or the highs? If you can sort that out, you’re well on your way. Even if you can’t, you’re still going to be able to figure it out. It will just take a bit more trial and error.

To begin, pick a section of the EQ to adjust. If you have a bandwidth (Q) control knob or button set it at its narrowest setting. Then take the frequency knob, and turn it all the way to the left, at its lowest setting. Finally, take the level knob, and slowly turn it pretty high, to around three o’clock or so. Now, while listening to the sound, slowly turn the frequency knob to the right, listening for when that nastiness you’re looking to get rid of becomes the most loud and obnoxious. Sometimes this will happen in the form of feedback, in which case you shouldn’t worry, just stop when you hear it start to hum or squeal, because you’ve found the first frequency you need to adjust. At other times, the unwanted sounds will be more subtle.

Once you’ve found the culprit, take the level knob, and turn it back past 0, and start to cut that frequency. A good rule is to start with a cut of minus three, and adjust from there; it’s rare that you’ll need something more drastic. If you do, odds are you can fix it by moving the microphone or choosing one that is better suited to that voice or instrument, which is always the better solution.
If you have a bandwidth or Q control, the final touch is to slightly widen that bandwidth setting. While a real narrow setting makes it easier to find the offending frequency, you’ll find that in most cases, a small, medium-wide cut does a lot more good than a deep, narrow one.

If the sound still isn’t quite right, try moving to another EQ section on that channel and doing the same thing; often you’ll need a couple of EQ adjustments on the same input to get things in gear. A good rule, though, is to try to avoid using more than two EQ adjustments on any one input. More than that suggests that you’re better off moving or replacing the mic itself.

Once you’ve had some practice with this method, you can start out by turning the level knob all the way down instead of all the way up. This is more subtle, so it’s less obnoxious to those who have to listen to it, but it’s a bit harder when you’re new at this. Don’t worry if you can’t get the hang of it right away. In this case, you’re listening for when that nasty part of the sound goes away, instead of when it’s at its loudest. Again, once you find it, you’ll adjust the level (in this case, turning it back up a bit so it’s not as drastic a change, and widening the bandwidth a bit, just like before).

If you do this for a while, you’ll find that you quickly start to learn what different frequencies sound like by checking the knob to see what frequency you’ve ended up adjusting once you’re done. Eventually, you’ll learn to recognize these,  and immediately know, “Oh, that sounds pretty awful around 1600 Hz, let’s turn that down a bit.” Until that time, you’ll have this system to fall back on, and you don’t have to be intimidated by those numbers.

Just between us, even though I’ve got years of experience doing sound for big touring theatre and arena shows, sometimes I’ll get a tricky sound that I just can’t get a handle on at first, and I’ll use this trick to get it dialed in quickly, too.

Now you know enough about EQ to start practicing, and we can all do our part to make the world a better sounding place. ?

Equalization controls

The EQ section for a single channel of a typical audio console, this one an Allen & Heath GL4800. For each of the four frequency ranges—top to bottom, high, high mid, low mid, and low—the green knob allows the operator to select the specific frequency to be adjusted, and the pale blue one controls the level of that part of the signal. The Q switches on the high mid and low mid controls adjust the width of the selected frequency band.

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