E.Q. Basics | Wanna Play Music

This section may appear to be a science lesson. However, it contains really good reference material for the day you are setting up your bands PA for that first gig. It's pretty dry on the surface, but may come in handy one day soon.

Everything about a mixer is designed to help you control the sound of the instruments that you are miking or getting a signal from. Probably the most important part of using a mixer is knowing how to use EQ (short for equalization, which is a fancier name for "tone control"). You can think of the equalizer controls on a mixer as a set of tone controls much like the bass and treble knobs on a stereo amplifier. The difference is that many mixers let you choose the range where the lows and highs are boosted and cut.

Okay, it's science time. Sound is vibrations in the air. The speed at which vibrations take place is known as frequency, and low-frequency vibrations produce low pitches, while high-frequency vibrations produce high pitches. Every pitch, every note, has its own frequency. And, frequency is measured in vibrations, or cycles, per second. Scientists decided to call "cycles per second" by the name Hertz. Knobs on mixers and other equipment that control frequencies have numbers followed by "Hz," which is short for "Hertz." Ah-ha.

In the real world, no sounds you hear are purely one frequency. Any pitched sound you hear, like a note on a piano, is actually made up of a basic frequency, called the fundamental, and any number of higher frequencies, known as overtones, partials, or harmonics. The fundamental frequency is the pitch you recognize, such as middle C on the piano, or low E on a guitar. The overtones create the sound's characteristic timbre (pronounced TAM-bur), or tone color. Because many instruments can play a note such as a C, it's the arrangement and intensity of the overtones that tell your ear the difference between different instruments.

The range of all possible frequencies is called the frequency spectrum, and the part that humans can hear is known as the audio spectrum. The audio spectrum extends from 20 Hz to 20kHz (kiloHertz, or thousands of cycles per second). Any portion of the frequency spectrum is called a band. It may be very wide, as in the range that a synthesizer can play, or it can be narrow, like the average range of the human voice's fundamental frequencies, from about 80 Hz to 600 Hz.

A band's narrowness or wideness, measured in Hertz, is called its bandwidth. Some equalizers give you control over the bandwidth of one or more bands. The general frequency of each band is determined by setting a center frequency that, appropriately, lies at the center of the band. Once the center frequency and bandwidth are set (assuming those parameters are variable), the band can be boosted (increased) or cut (decreased) in level. Some equalizers have preset frequency bands, and you can only boost or cut them. In such cases, you might not have as much flexibility as you would want, but at the same time, there's less knob twiddling that you need to do.

Types of equalizers
There are two basic EQ designs: graphic and parametric. A graphic EQ divides the audio spectrum into a number of preset bands of equal width, and allows you to individually boost or cut each band. Many home stereos have graphic EQs, and you can hear their effect by moving their slider controls up or down. The more bands and the greater the amount of boost and cut, the more precisely you can control the effect. Since the boost/cut amounts are usually determined by the positions of vertical sliders on the unit's front panel, a graphic EQ gives you a visual representation of how it alters the input; hence, the name "graphic." Some mixers have graphic equalizers built in, and there are many stand-alone graphic equalizers available for connecting to a mixer.

A parametric equalizer breaks the frequency spectrum into only a few bands, but it gives you control over three parameters that define each band: center frequency, bandwidth, and boost/cut amount. While graphic EQs offer a wide but preset selection of center frequencies, parametrics allow you to zero in on exactly the frequency you want, such as the sizzle of a snare drum's snares. With a parametric EQ you can narrow the effect to emphasize just the brightest portion of the snares, or widen it to emphasize a broader, heavier part of the snare drum's spectrum. The boost/cut control on a parametric is the same as the boost/cut control provided by graphic equalizers. The equalizers provided with each input channel of a mixing board are usually parametric.

Many mixers have a variation on the parametric concept, called quasi-parametric EQ. A quasi-parametric may give you control over center frequencies but not bandwidths, or it may give you parametric control over the low-range and midrange bands while providing only boost and cut for the highs.

Which is better, graphic or parametric? Neither. It all depends on what you want to do, how much control you want, and how much you're willing to spend for the amount of control you need. Confused? Work with a mixer for a while, and the confusion will fade away.

Using EQ
Using an EQ is mostly a matter of training your ear to find problem frequencies, and then knowing how to deal with them. You'll have to learn to EQ each mike (or instrument), as well as the band as a whole. Ready? Go!

The first challenge is finding a band that needs adjusting. Then you have to adjust it. For instance, let's say that the snare drum sounds muddy. Go to the channel on the mixer that controls the snare drum's mike, and get busy.

Start at a point obviously below it and boost successively higher bands. On a parametric, simply crank up the boost knob and then sweep the range of center frequencies. If you're using a graphic EQ, this involves turning each boost/cut slider up and down in turn until the area of the sound you're interested in jumps out at you. Don't worry about missing it, because it will be very obvious.

Once you've found the proper band, decide whether you need to affect a narrow bandwidth or a wider area. With a parametric, you can simply adjust the bandwidth knob. With a graphic EQ, try turning up and down the bands on either side of the center frequency you've selected. Once you're satisfied, either boost or cut as needed.

If there's any one big mistake you can make with EQ, it's using the boost too much, and the cut too little. It's often said that a cut is as good as a boost, but it can be even better, if it can achieve the effect you're looking for. For example, if you want to emphasize the upper midrange frequencies on a guitar, instead of boosting the upper mids, try cutting the lower mids. Want to strengthen the bass? Try cutting the treble.

Why is cutting so good? This is because anytime you boost, you raise the overall level of the signal. When you raise the level too much, you can cause the mixer to distort. This can be tricky, too, because you might boost several mikes' signal levels and not notice a problem while each everyone is playing softly, or only one instrument is playing a loud solo, but as soon as everyone starts to play loud together, the P.A. starts to distort.

Another thing to keep in mind: All signals have some noise in them (usually a little hiss), so when you boost anything, you also boost the noise. So, that's another reason why cutting is such a good thing.

Also, any time you boost a signal, you boost some noise, as well, both noise in the signal and noise in the EQ unit. So always consider cutting before you decide to boost.

Most of the time you'll be EQing individual instruments to make up for one deficiency or another, or to make it fit into the overall mix better. But you'll also be called on to EQ the entire mix so that the band, as a whole, sounds its best. Practice both, and if you can work with, say, a drummer or a guitarist or a singer by themselves, you can really develop a fast hand at EQing them, which will make your life as a sound person a lot better when you're under the pressure of a real, live gig.