XO Wave: How to Use EQ (Audio Equalization)

A Graphic EQ is one of the most recognizable pieces of audio gear.

EQ (equalization) is probably the most important effect at your disposal as an audio engineer. EQ, compression, and reverb make up the basic effects of virtually any modern mix. Of the three, EQ is probably the most misunderstood and most misused. This tutorial will help you understand how to use EQ effectively, and apply it to virtually any situation. If you are looking for info about XO Wave's built in EQ, or you have never used an EQ before, you may want to read our Article on XO Wave's EQ, which not describes the basic types of EQ and their most common uses.

General EQ Tips

There are no hard and fast rules of EQ except that practice makes perfect, but these tips should help you avoid some common pitfalls, and give you a starting point for virtually all your EQ needs. Although later sections give some tips for specific instruments, most of that information is simply a matter of applying these general principles.

• Use your ears: You may read or hear that some engineer always adds a certain amount of a certain frequency to a certain instrument. This may work if the engineer is always recording the same song on the same instruments the same way all the time, but in the real world, you have to use your ears before and while you are adjusting the EQ. While it can be very useful to know what 400 Hz sounds like, don't bother memorizing frequency/instrument combinations that people claim they use. Sure, you may often find yourself boosting or cutting a certain frequency, and maybe that's a good starting place if you happen to know that the particular instrument you're working with has a particular sonic defect, but it never hurts to take a second and listen to the track 'flat' (without EQ) in the context of the rest of the mix before you start turning knobs.
• Less is More: Most people, when they start using EQ, tend to use it to increase frequencies to bring out certain aspects of a sound. While this type of EQ certainly has its place, it is usually the wrong way to go about working with EQ. The temptation to have more of whatever it is (e.g., more bass, more presence, etc) is often reinforced by the fact that increasing the EQ level increases the volume of the track. The trouble is that after adding a little here and a little there, a mix can end up sounding dull and muddy. Each track may sound great on its own, but doesn't necessarily work well with the mix as a whole. Rather than adding EQ, try and think about what you can take away, instead. For example, if your guitar needs to be more present in the mix, try reducing the bass with a shelving filter instead of adding a "presence peak" with a Boost/Cut filter. Another trick, which we'll say more about in a minute, is to think about other instruments that are competing with the guitar and try and reduce some of the competing frequencies in the other instrument.
• Listen to the mix: If you are EQ'ing one track in a mix, it can be helpful to solo the track to find the right frequencies. If you do this, however, be sure to always listen to the track in the mix before committing to any particular settings. This will ensure that your settings work not just in isolation, but also in the context of the song. Remember, your job as audio engineer is not to make any particular instrument sound as good as possible, but to make the song sound as good as possible.
• It's all about balance: In a complex pop mix, it is common to have many instruments competing for the listener's attention. A good pop arrangement typically only has one instrument that demands the listeners attention at one time, so it's important to focus on that. Instead of cranking the volume or EQ of the lead instrument, try using EQ to cut some of the other instruments out. With your other instruments, make sure that each track occupies a distinct frequency range. For example, The kick and the bass often compete for the low frequencies, and can sound very "muddy" together. A solution to this problem is to have one of them occupy the extremely low frequencies, say, below 80 Hz, and the other to occupy a slightly higher range, say from 100 to 220 Hz. This gives each instrument a distinct "space" for it to be heard in, and results in a much more pleasing overall sound than trying to get the instruments to mesh by trying to balance the volumes.
• Give and take: If you do end up boosting a certain frequency range in one track, it is a very good idea to think about what other instruments might already be occupying that frequency range, and reduce those frequencies, so that the first track has less competition, and, therefore, requires less EQ.
• Buzz Words: Many engineers, producers and musicians use terms like "thud", "thwap" and "air" to refer to certain aspects of sound. This may sound absurd to outsiders, but terms such as "shimmer" often have very specific meanings between people who are familiar with each other and share terminology. While there are widely accepted and used definitions of these terms, they are not really standardized and often misunderstood, so it's wise to be careful with them. That said, such terms are necessary for describing audio characteristics which normal English isn't equipped for -- just remember that your idea of "chunky" may be different from someone else's.
• Compensating for problems: EQ can be used to compensate for a variety of problems. For example, you can use a band-stop filter to eliminate narrow-band noise or even a bad echo. Sometimes, you may be stuck with a poorly recorded track and no option for re-recording. EQ can be a real God-send at these times for solving all kinds of problems. As with other EQ techniques, be careful, use your ears and listen to the track in the context of other tracks. When trying to eliminate a problem in a particular frequency range, use a Boost/Cut filter. Start with the level set all the way up and then move the frequency slider around until the problem gets worse. Then move the level slider back down so that that you are eliminating the "bad stuff."

EQing Vocals (and Other Lead Instruments)

In general, vocals are the most important and most prominent instrument on any given audio project, and even when that's not the case, whatever is the most prominent instrument should usually be treated with the same care as vocals. Unfortunately, it's very easy to ruin a complex instrument like the human voice with poor EQ. Because of its prominence, any mistakes you make in the vocal track will stick out like a sore thumb. The best way to EQ vocals is usually to change them as little as possible.

If you start with a great vocal recording you should not need to do much. If you think you have to use EQ anyway, either because it was poorly recorded or doesn't work well in the mix for some other reason, stop and think about the tips above. For example, many engineers try to get more vocal presence by adding some mid frequencies to the vocal track. This certainly makes the vocal more prominent, but it probably sounds harsher, too, which may not be what the song calls for. Instead, try decreasing that frequency range in other instruments (such as guitar or snare) or, as a last resort, try shelving off some of the low frequencies in the vocals, which can often accomplish the same effect with less harshness.

Two special considerations with vocals are sibilance and popping. Sibilance is an exaggerated high frequency sound (especially on the letters "s", and "f"). Although sibilance should be minimized during tracking, sometimes it isn't and very often processing such as compression, EQ, or reverb can make it quite serious, even if the original track was well recorded. Sibilance should not be handled with traditional EQ. Instead, use a de-esser, which is a special setting on a compressor, that uses EQ to make the compressor more sensitive to high frequencies. Popping sounds can and should be dealt with entirely during tracking, but if it's already too late, you can usually use a combination of compression, EQ (typically a high pass filter), and volume automation to eliminate the problem.

EQing Acoustic Instruments

Much of what applies to vocals and lead instruments applies to acoustic instruments as well. The general rule is that the best recordings are made when the original tracking sounds great. If you find yourself needing lots of EQ, consider re-recording the track instead.

If you are recording an acoustic singer/songwriter or duet, their instruments and arrangements will (hopefully!) be chosen to complement one another rather than to compete, but if you have a nasal-sounding guitar and a nasal-sounding singer, you'll need to do some EQ -- in this case, you'll probably want to make the guitar less nasal, but some experimentation may be needed.

If the instruments were close-miked, they may have too much bass, which can muddy the mix. By rolling off a little bass, you can compensate for this, which can help tighten up the entire mix. It can also be helpful to roll off the bass to reduce stage rumble.

If your recording is hissy, from ventilation or other noise, you might be tempted to reduce the high frequencies as well. Unfortunately, you'll probably find that doing so kills the spaciousness and detail of the recording. Generally speaking, acoustic instruments have high-frequency components that are so important to how they sound that you really want to keep them. If the noise is bad, the best solution will depend on the mix: you may want to use volume automation, a noise-gate, or even broad-band noise reduction to tackle the problem.

EQing Drums and Percussion

Nowadays, drums are often individually close-miked. While this gives a certain amount of flexibility, and reduces the need for an acoustically balanced drum room, it can sound unnatural in a variety of ways, and, as a result, drums generally require a lot of processing to get them to sound natural (assuming that's the goal). I usually start with the kick, which I EQ at the same time as the bass to ensure that they don't compete for the same frequency range. From there, I work on the snare, trying to get it to sound generally correct, and then I add the rest and EQ some more.

Because the drums cover such a broad range of frequencies, and because the kick and snare often contribute significantly to the sonic "signature" of the song, I often find myself going back to the drums throughout the mix process. Producers are picky about the snare and kick, so be sure to give them your full attention, but also remember that you have other tools at your disposal, such as compression and reverb.

EQing Bass Guitar

EQing bass can be a great opportunity to get creative. Often, bass is recorded "direct" without going through an amp, and it can sound limp or flat without the analog processing a good bass amp can offer. However, a good parametric EQ, used with imagination, can result in great sounding bass -- just remember not to compete with other instruments, particularly the kick drum.

If, on the other hand, the bass was recorded with a miked amp or amp simulator, you may not have much work to do aside from balancing the bass and kick, but don't forget that the bass guitar has a lot of harmonics that can also compete with other instruments including the guitars and vocals.

In general, don't forget what the bass is there for: bass. Be sure to make it strong in the low frequencies, and just strong enough in the high frequencies to be as present as is needed.

Electric Guitar

Generally, guitarists are the most conscious of their sound and will create the sound they want with the settings on their guitars, effects pedals and amps. Unless you have reason to second-guess them, you generally want to respect that sound. So while you may change the general low/mid/high balance of their sound, you don't want to do anything too extreme. The most common exception is when the guitar competes with vocals. In this case, nine times out of ten, you want to cut the mid frequencies in the guitar to let the vocals breathe.

Some people try and solve the guitar/vocal competition problem by using lots of compression, or with a trick like stereo panning. This may work up to a point, but it often doesn't translate well into the real world, where small mono speakers are the norm. One trick that does work well, however, is to use automation to change the EQ settings on the guitar so that there is less mid-range sound when the vocalist is singing, and more when they aren't.

Conclusion

EQ is probably the most important effect at your disposal as an audio engineer. It can be used to solve problems, to create special effects, and, perhaps most importantly, to help instruments blend together correctly. If you remember to always listen and are willing to experiment, you will master the subtle art of EQ!

-- Bjorn Roche