EQ: two letters that can mean a lot to the sound of your videos.

Though far from being a “magic wand” to eliminate problems from your soundtrack, the equalizer (EQ) is one of the handiest audio tools for videography. Whether found in an audio mixer or mounted in a rack full of audio processors, an EQ gives you control over the tonal balance of your audio. It can also help eliminate unwanted noise, reduce tape hiss or zap a nasty audio buzz.

The Basics

Before we dig too deeply into equalization, let’s cover some important basics of sound.

Sound is nothing more than a series of tiny, up-and-down changes in air pressure. How fast these changes occur defines a sound’s frequency. To our ears, frequency corresponds to how “high” or “low” a sound is (in music, we refer to this as a sound’s pitch). We measure frequency in cycles per second or Hertz(abbreviated “Hz”). The human hearing range spans from roughly 20Hz on the low end to 20,000Hz (or 20kHz) on the high end.

Though we often refer to a sound as having just one frequency, common sounds carry energy at numerous frequencies. The human voice, for example has a relatively low-frequency fundamental (the lowest, strongest sound). Above this are countless higher frequency sounds that are responsible for intelligibility–these change with each vowel or consonant.

When you hear (or your camcorder records) multiple sounds at the same time, you re picking up a complex wash of thousands of different frequencies. The balance of these frequencies–which ones are strong, and which ones aren’t–goes a long way towards defining the quality of the sound we hear.

Frequency Fixer

Though it has a lofty-sounding name, the definition of an equalizer couldn’t be simpler: an equalizer is a device that changes the strength of a range (or band) of frequencies. How much control you have over that band of frequencies depends on the type of equalizer you re using.

When we make a range of frequencies louder, we re boosting that band. When we make them quieter, we re cutting those frequencies. Boosting or cutting frequencies is the simplest form of control an equalizer will give you (see figure 1). In technical terms, we refer to this as changing the frequency band’s gain.

The next level of control involves manipulating bands by their location in the sound spectrum. When the band of frequencies falls low in the human hearing range (usually under about 200Hz), we call it a low-frequency band. Between 200Hz and about 6kHz are the mid-frequency bands, while 6kHz on up is the realm of the high-frequency bands. See figure 2 for more info.

The last characteristic of equalization defines how wide a chunk of frequencies is affected. We call this bandwidth, and it can range from a very narrow slice of frequencies to a very broad band. Narrow bandwidths are useful for solving problems at a specific point, while wide bandwidths are more suitable for broad tonal changes. In use, the difference between narrow and wide bandwidths is like the difference between a circular saw and an X-ActoTM knife.

This type of EQ affects a set range of frequencies, without changing those that lie above or below it. However, the most common type of EQ uses a slightly different approach. Called a shelving EQ, it affects everything above or below a given frequency by the same amount (see figure 4). Because it affects such a wide range of frequencies, shelving EQ is most useful for changes in the overall sound.

An EQ Tour

Starting with the simplest and moving to the most complex, let’s take a quick tour of the various types of EQs available.

Bass and Treble Controls
Like the tone controls on a home stereo, this simple two-band EQ has high- and low-frequency shelving controls. The bass knob controls the level of everything below a certain frequency, while the treble knob changes everything above a certain frequency. Midrange frequencies are on their own. This type of EQ is most common to small audio mixers and stereo receivers.

What it’s good for: broad tonal changes. If your audio sounds “dull” overall, boosting the treble or cutting the bass may help. If it sounds too thin, try the opposite: cut treble and boost bass. This type of EQ doesn’t offer enough control for precise sound tweaks.

Three-band EQ
This type of EQ adds a midrange band to the shelving bass and treble controls. This midrange band usually has a traditional bell-shaped response (for a refresher, see figure 1b). Three-band EQ is common on mid-priced audio mixers.

What it’s good for: broad tonal changes. Though it offers more control than simple bass and treble controls, the three-band EQ still doesn’t offer enough control to pinpoint and eliminate problem sounds.

Three-band EQ with sweepable midrange
Instead of fixing the midrange control at a set frequency, this type of EQ allows you to move the mid band through a range of frequencies. More up-scale audio mixers offer this type of EQ. To attach a snazzy term to a simple concept, EQs that give you control over gain and frequency (but not bandwidth) are semi-parametric.

What it’s good for: broad tonal changes. The sweepable band gives you more control over midrange frequencies, but its bandwidth is usually quite broad.

Three-band EQ with fully parametric midrange
This type of EQ allows you to control the gain, frequency and bandwidth of the midrange band. Called “fully parametric,” this type of EQ gives you maximum control over your sound. High-end mixers frequently offer fully parametric EQ.

What it’s good for: broad tonal changes and precise problem solving. The upper and lower shelving controls allow broad changes, while the mid band can go from extremely narrow to broad at the twist of a knob.

Four-band EQ
This type of EQ adds a second midrange control. Like the three-band varieties listed above, these mid bands can be fixed-frequency, sweepable-frequency, or fully parametric. With the latter two (most common), the frequency ranges of the two midrange bands often overlap. This allows you to “stack” the two controls at the same frequency for severe correction. High-end audio mixers sometimes boast four-band EQ.

What it’s good for: broad tonal changes and precise problem solving. Having two mid-frequency bands to adjust gives you that much more control.

Graphic EQ
This type of EQ usually offers between five and 30 bands of equalization. We call these “graphic” equalizers because the position of the vertical gain sliders gives you a rough picture of the correction applied. Graphic EQs offer fixed frequencies and bandwidths, usually designed so one slider doesn’t have a radical effect on adjacent bands. You ll sometimes find small five- and seven-band graphic EQs on audio mixers, while EQs with more bands are usually stand-alone (or “outboard”) devices.

What it’s good for: broad tonal changes (fewer bands) or precise problem solving (many bands). Because the number of bands dictates the width of each one, EQs with just a few bands affect large sections of the audio signal. EQs with 15 or more bands are generally better for fine adjustments than broad tonal correction. Keep in mind that a graphic EQ’s frequencies are fixed–you won’t get perfect results if an unwanted sound falls between two sliders.

Three-, four- or five-band fully parametric EQ
This type of EQ is a real audio “power tool.” It offers several fully parametric bands that allow you to control gain, frequency and bandwidth. On some EQs, you can even flip the highest and lowest bands into shelving mode. You ll find multi-band fully parametric EQ in a dedicated, outboard device almost exclusively.

What it’s good for: any EQ application. The fully parametric EQ works like a charm to make broad tonal changes or microscopic fixes. At one extreme, this EQ will go wider than any fixed-bandwidth EQ. At the other, a fully parametric EQ will cut out a finer slice of audio than even a deluxe graphic EQ. For hunting down and eliminating a buzz, hum or other distracting noise, fully parametric EQ is the way to go.

EQ Fixes

Problem Possible EQ Fix Best EQ
Overall sound too dark boost treble
reduce bass
reduce low mids
any
Overall sound thin, tinny boost bass
reduce treble
boost low mids
any
Speech boomy and indistinct reduce low mids
boost upper mids
semi-parametric
 
Annoying AC buzz cut 60Hz (and multiples of 60) graphic or parametric
Pronounced tape noise (hiss) reduce treble any
Loud wind noise reduce lowest bass frequencies graphic or parametric
Too much mike-handling noise reduce lowest bass frequencies graphic or parametric

–LA

Contributing editor Loren Alldrin is a freelance video and music producer.

Diagram Captions:

1. An EQ can change the frequency band’s gain by boosting or cutting the frequency.

2. A band of frequencies can fall in the low, mid or high range of human hearing.

3. Bandwidth defines how wide a chunk of frequencies an EQ affects.

4. A shelving EQ affects a set amount of a defined frequency.

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