In Part 1 of this series we talked about frequencies of sound and some basic principles of equalization (EQ). Now let’s look at the most common types of EQs you are likely to encounter and how to use them to take control of your sound. Because each type of EQ has an application to which it is best suited many amp makers offer a combination EQ section to give you the best of each in a practical package. We’ll use the Carvin Audio BX700 bass amp combination EQ to explore each of these types but you’ll find these controls are quite universal once you know how they work and how to recognize them.
The most common EQs you will see are low shelving (bass) and high shelving (treble) filters. These allow all frequencies beyond a preset point to be unaffected while the knob affects the volume level of the rest. There are also midrange filters called band pass filters which affect a range of frequencies in-between. These simple filters are the standard tone knobs you see on most guitar and bass amps, though various active or passive circuits affect whether they can only boost, cut or do both. Active systems as supplied on the BX700 are flat (no effect) in the 12 o’clock position and can both boost and cut frequencies within the designated range.
For greater control and versatility, some amp designs offer quasi-parametric controls for one or more midrange bands. On our sample amplifier there are two quasi-parametric mid controls. These powerful EQs have two controls, one for level and one to select the center frequency. Usually if there are two or more of them each will offer a slightly different range of frequencies, such as hi mid or low mid. Because they can zero in on any frequency in the range, these are great for overcoming ‘dead-spots’ on your bass guitar or eliminating runaway feedback on your acoustic guitar. Adjust them quickly by overemphasizing the level of boost or cut while sweeping the frequency control to find the target frequency fast, and then readjust the level for optimal musical balance.
These first two types of EQs also appear in the channel mixing strips on most sound mixers as well, so next time you have to decipher the sound-board you’ll have an inside track on dialing in the channel EQs.
For increased versatility in pinpointing specific frequencies the graphic EQ is a very useful tool as well. These are essentially like your standard bass, middle and treble controls in function, but control a lot more individual frequency bands. You’ll find graphic equalizers with as few as 5 bands and as many as 64. The more bands on the EQ the narrower the range each of them controls. Graphic EQs are very powerful but can be tricky to properly adjust quickly. But because of their narrower bandwidth they are useful for tailoring the sound system to the room acoustics or eliminating feedback in monitor systems. When you find them on guitar and bass amps they can be great for a switchable ‘boost’ for solos.
Another type of EQ control that you might find are “contour” controls which give you a fast way to dial in the midrange character of the amp from “fat” (midrange heavy) to “scooped” (midrange attenuated). They can be great for compensating for the differences between one guitar and the next without losing your entire EQ setting, or for a convenient and foolproof way to adjust the overall tone character of the amp with one turn of a knob. Some designs also offer tone switches that boost or cut a predetermined frequency and amount; “Bright”, “Fat”, “Presence”, “Thick” and other controls with a single switch work this way. Try it out and use it if you like it. Amp designers are pretty good at creating these little one-shot “wow-buttons” and they offer another convenient way to adjust your tone quickly.
When approaching equalization remember to follow the “less is more” principle. In order to make their effects more practical and “musical” there is a degree to which the frequency bands overlap. Setting all your EQ controls to maximum or minimum settings can make the tone seem “unnatural” by overemphasizing the center of each EQ band or cause distortion if you push them to the extremes.
With a little practice and experience, you’ll find that you begin to know intuitively how to use each type of EQ to tailor your sound to your liking. Spend some time exploring the EQs on each of your amps and mixers so you understand how they work individually and together. Equalization probably still won’t seem as exciting as a great delay effect or a lush chorus, but you might begin to appreciate why so many top professionals talk about EQ more than any other type of signal processing.