WHEREVER YOU TURN IN THE LAND OF AMPLIFIED bass, some form of EQ is there to greet you. You’ll find it in most onboard bass preamps, in effect pedals, in bass heads, and in many different studio components. Combine its prevalence with its unparalleled power to shape your tone, and it’s obvious why understanding how to use it is critical for the intrepid tone explorer. But despite its ubiquity, many players are hazy on nittygritty EQ details. An equalizer (EQ) is a circuit that can change an audio signal’s tone by boosting or cutting various regions (bands) of its frequency content. Equalizers can be broken down into two basic types: parametric and graphic. Parametric EQs give you complete control over the frequency center, bandwidth (or Q), and gain (boost or cut). Parametric EQs are more complex in terms of the number of controls; you need a good technical understanding of its operation to use one effectively. They have ultimate flexibility but can be cumbersome, even for the technically advanced, and are not well suited to on-the-fly adjustments other than the most basic ones. A graphic EQ, on the other hand, has fixed frequencies and bandwidths. It is less flexible, but it’s much easier and more intuitive to use and therefore more conducive to on-the-fly adjustments. Any band of an EQ circuit has two critical parameters: center frequency and Q. Unfortunately, except on fully parametric EQs, you ordinarily cannot change an equalizer’s Q value. But I’d like to include Q values in my discussion of EQ circuits anyway, because this knowledge will help you read a manufacturer’s spec sheet to get a better idea of what to expect from a particular equalizer. The treble band is probably the most important in terms of an EQ circuit’s effect on your tone. Some general guidelines: When using active pickups, a 6kHz–7kHz center frequency, with a Q of around 1.5, is good for jazz fusion and funk playing. Boosting this frequency band will give a nice, crisp response to popped strings without adding harshness. Most passive pickups, though, do not have adequate response up this high; if you boost in this range you’ll probably end up only increasing noise. So avoid boosting in this range if you play basses with passive pickups. A 5kHz–6kHz center frequency with a Q of 0.8–1.2 is a good general-purpose treble control; it will have the flexibility to address many different styles without becoming harsh or adding excessive noise. It will also work well for either active or passive pickups. If you’re a rock-oriented player, a 4kHz center frequency with a Q of 0.7 to 1.0 will give you a harder attack, which can help in cutting through the mix, but the tone can become harsh if you boost too much in this range. It’s important to know whether an EQ circuit is the peaking or shelving type. A shelving EQ boosts or cuts all frequencies above or below a certain frequency, sometimes called the “knee.” Since shelving controls work with a much broader range of frequencies, a shelving treble control, for example, tends to produce a very “airy” sound that can be made very bright and articulate. However, shelving treble controls can also add large amounts of noise if you boost excessively. I prefer shelving treble controls to have a knee of at least 4kHz; otherwise they can sound harsh and “clanky.” Next on the list is the bass control. Boosted frequencies in the 20Hz–30Hz range can often be felt more than heard if the Q is much higher than 0.6. For a good, all-around bass control, I prefer a low Q of around 0.3 and a frequency of 30Hz–40Hz. This adds depth and bottom without sounding too boomy. A 20Hz–30Hz center with Q of 0.6 or above provides a very “sub-bass” sound that works well for reggae or hip-hop. Bass controls in the 60Hz–100Hz range can make your bass sound louder in the mix, as they are boosting 2nd harmonics more than fundamentals—but your tone can easily become too boomy if you over-boost this range. Last is midrange. I could have mentioned this band first, as it has the most potential for totally ruining your sound—use this control judiciously! For bass guitar, I find midrange frequencies in the 500Hz–1kHz range, with a moderate Q of 0.4–0.7, to be most useful. Boosting can increase punch and presence in the mix, and cutting can hollow out a slap sound nicely—but too much cut will get you lost in the mix. I tend to limit boosting midrange to no more than a few decibels; if you boost too much, you may find it difficult to blend into the mix properly. A lot more can be written on the subject of EQ, but this should be enough to get you off to a good start. Good luck in your search for tone.
	—Seymour Duncan Basslines Chief Engineer Kevin Beller has been with the company for 18 years, starting when Seymour and Cathy Duncan were winding pickups in their garage. Prior to that, Beller worked in the computer industry, specializing in process development and machining techniques for ceramics. Armed with several years of electronics classes in college and a few books, such as The Radiotron Designer’s Handbook, Beller went on to engineer the majority of Duncan’s bass pickups.
	Orginally published in BASS PLAYER magazine. Copyright © 2006 CMP Entertainment Media. All rights reserved. Used by permission.