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EQ Explained: All Things Are Not Equal

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Thanks to the development of low-cost, high-quality digital recording gear, the world is now populated by people who record their own music, yet have never touched a soundboard. While we applaud this healthy trend, there’s still plenty of old-school know-how that can enhance the recording experience. Not the least of which is an understanding of equalization. It can be your best friend or worst enemy while tracking and mixing music, and there are countless opinions about EQ. We’re going to touch on some fundamental truths about the topic to help you optimize your studio drum sounds.

Preparation

The best way to use EQ is sparingly, or even not at all. And to do so, you need to make sure your drums sound so damn good that you won’t have to touch a knob on the equalizer. Sure you can use equalization to hide an offending sound, but whenever you decide to “fix it in the mix,” you run the risk of diminishing the overall integrity of the recording. It’s best to solve your sound problems early in the process.

Always ask for suggestions. Before you start turning knobs, try new tunings, experiment with heads and change miking configurations. Also, if it’s not broken, don’t try to fix it. People who wouldn’t dare touch an equalizer if their lives depended on it have recorded some of the best drum sounds that I’ve ever heard.

Acoustical Principles

With that said, let’s talk about how equalizers affect the way our ears perceive sound waves that come from a pair of speakers. Let’s start at the beginning. When a stick hits a drumhead, the head is pushed down and in reaction pulls back up, like a spring. This fluctuation causes the air molecules immediately around the head to compress, then return to their normal pressure. The energy from these molecules is then passed on to the molecules around them causing a chain reaction.

The fluctuation of air pressure makes the drum shell and bottom head vibrate sympathetically, causing even more complex fluctuations of air pressure. This expanding of high and low pressure is called a sound wave, and the number of times that the pressure fluctuates from its maximum to minimum in one second is called the frequency.

Sound wave frequency is measured in Hertz (Hz) in honor of Heinrich Hertz, who made many contributions to the study of sound. One cycle per second = 1Hz. The vibrations of the drum cause many different sound waves, with a large variety of frequencies. For instance, the stick hitting the head creates the highest frequencies. And the resonation of the shell and bottom head creates the lower frequencies. An equalizer will allow you to raise or lower the amplitude (volume) at different frequency bands. So if you wanted to increase the attack of the drum, which would be the stick hitting the head, then you would use the equalizer to raise the amplitude of the higher frequencies.

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Fig. 1

Types of Equalizers

The three most common types of equalizers are parametric, graphic and shelving equalizers. Graphic equalizers have anywhere from three to 31 fixed frequencies that allow you to raise or lower the amplitude. They commonly span from around 20 Hz to 20 kHz (20,000 Hz), which represent the range that humans can hear sound with distinction. Drums often create frequencies above and below these limits, but our ears simply cannot detect them.

When you raise the volume on a graphic EQ at 1 kHz, you will also raise the frequencies around it at a fixed bandwidth set by the manufacturer. This affects the amplitude at frequencies from 300 Hz to 5 kHz (see Fig. 1). With a graphic equalizer you can apply many more cuts and boosts to a wide range of frequencies than you can with other equalizers. But the disadvantage is that you have to apply these at frequencies set by the manufacturer – you cannot adjust the bandwidth of the boost or cut.

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