By Shure Notes Editors, Contributors: John Chevalier and John Mills
In its simplest definition: Equalization involves selectively boosting or cutting bands of frequencies to improve the performance of a sound reinforcement system.
Like many other audio technologies, EQ was born in telecommunications, where filters were used to restore and flatten all frequencies, so that response to all frequencies would be equal – hence the label “equalization”. Hollywood came on board in the early 1930s with the emergency of ‘talkies’, but it wasn’t until the late 1950s and early 1960s that Texas academics in the field of Physics did research that led to precursors of today’s pro audio technology. By the 1980s, graphic equalizers on our home stereo systems were the portals to EQ and many of us had a good time adjusting the sliders.
In the natural world, the sounds we hear are incredibly complex. As we walk down a city street, we hear the rumble of a subway train, a police siren, the boom-boom-boom of an enhanced bass car stereo passing by or the voice of the person walking next to us. But in a live sound or recording situation, none of us wants the listener to either cover his ears or struggle to pick out a specific sound source.
What equalization can do when used properly
- Noticeably, but not dramatically, improve the naturalness or intelligibility of a sound reinforcement system by emphasizing the frequency ranges most critical for speech.
- Noticeably, but not dramatically, increase the overall output level of a sound reinforcement system by reducing the system’s output in the frequency bands at which feedback occurs. These frequency bands will differ from system to system based on many variables, including room acoustics, microphone placement/design, loudspeaker location/design, even air temperature.
Expert Tip #1
“When running live sound, I occasionally run into a feedback situation. When this happens, I quickly determine the frequency that’s feeding back, and by that I mean, ‘Is it high-end feedback? Mid-range feedback? Or low-end feedback?’ Once I’ve identified that, I turn down the appropriate knob on the EQ. It’s fast. It’s easy. And it works every time.”
- John Chevalier
What equalization can’t do
- Make a poorly designed sound reinforcement system work satisfactorily. Every sound reinforcement system is subject to the laws of physics.
- Improve intelligibility problems caused by reverberation, reflections, mechanical vibration, high background noise levels, or other problems caused by the location or physical design of the room. These problems are acoustical in nature and can’t be solved electronically. They must be resolved with acoustical solutions, such as sound absorbent panels and heavy drapes.
- Improve intelligibility problems caused by the talker being too far from the microphone.
- Improve the performance of sub-standard audio components in the sound reinforcement system.
- Eliminate distortion or noise problems caused by mismatched audio levels between system components.
- Improve echo return problems in teleconferencing systems.
How to approach equalization
FOH engineer and touring pro John Mills likes to think of each song as a line, with each instrument making up part of it. If there are too many instruments or frequencies taking up the same space, the line gets bumpy and the mix gets muddy.
Expert Tip #2
Here are some general guidelines to consider when you’re trying to find your space.
20Hz to 80Hz: This is your sense of power in an instrument or mix. It’s the stuff you feel more then hear. The kick drum and bass guitar are down here in this range.
80Hz to 250Hz: The area where everything comes together. This is where a lot of things can go wrong and too much in here will make a mix sound sloppy.
250Hz to 2kHz: Most of your fundamental harmonics are in this range. These are some of the most critical frequencies to building a solid mix. Learn what instruments are most dominant in these frequencies and clean up around them.
2kHz to 5kHz: Here you will find the clarity to almost everything. But be careful, too much of a good thing can start to sound harsh. This is an area where subtly is the key.
5kHz to 8kHz: Mostly sibilance and “s” sounds. Much of the vocal consonants are defined in this range.
8kHz to 20kHz: Brilliance is the word here, the top end of cymbals.
“Becoming a master of EQ is like becoming a master painter. Sometimes you just have to throw some paint on a canvas and see how it works.”
- John Mills
Approach equalization gently and slowly! After every adjustment, listen carefully to the resulting sound. The goal is to improve sound quality as well as increase the gain before feedback. When the system is loud enough and/or clear enough, stop equalizing! Also, stop equalizing and examine the complete sound reinforcement system in detail whenever the equalization causes degradation in the sound quality.
JOHN CHEVALIER is a pro audio/video expert, writer and speaker at InfoComm, NAB and other industry events.
JOHN MILLS is a touring FOH engineer and the expert behind the TechTraining101 site offering sound advice for engineers at all experience levels.