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EQ Tips: When to Boost and When to Cut

by Daniel Dixon, iZotope Contributor December 18, 2018
Neutron 3 EQ

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I’ve read and heard many times that it's always a better idea to cut than boost with EQ when mixing audio. But in practice, there are many occasions where it feels natural and sounds better to boost frequencies. Lots of other engineers seem to boost all the time, and if we really weren’t supposed to, EQ consoles wouldn't include the option in the first place.

In this article, learn EQ tips on when to boost versus cut in a mix. Let’s start with some EQ basics.

What is EQ? And why do we use it?

Equalization is one of the simplest tools we have in our toolkit as producers, with stripped-down versions found in even home and car stereos. Its main function is to control the frequencies in an audio signal by boosting (additive EQ) and cutting (subtractive EQ) across the spectrum. Despite the simple function of EQ, it takes a lot of practice to be able to pinpoint problematic frequencies and make the necessary changes. But it all comes down to three controls:

Frequency: the frequency you want to manipulate

Gain: how much of the selected frequency you want to add or remove from the signal

Q: the shape of the EQ curve, from steep to wide

We use EQ because we don’t always want to hear the full frequency range of every instrument in a mix, and it allows us to bring out the best parts and remove the rest. There are also many creative applications of EQ when mixing audio, which we will touch on shortly.

Before diving in, it’s worth noting that all EQ moves should be done within the context of the mix. Doing this gives you a better understanding of how your decisions impact other instruments and the overall tonal balance. Its OK to reference tracks in solo to double-check decisions and other strange sounds, but keep this to a minimum.

Corrective EQ tips: cut

Corrective EQ fixes problems in a signal, like rumble and bleed, resonances, and other unpleasant frequencies. To correct a signal, most engineers cut a particular frequency band to attenuate or remove the issue entirely. I prefer to use corrective EQ before boosting anything else. Once I figure out where there is too much of something in a signal, it's much easier to determine what needs to be enhanced. For a starting point, clicking the Learn feature in Neutron’s EQ will intelligently place nodes across the spectrum on areas of interest (like those mentioned above) without gain or Q settings so you can tweak them to taste.

Being able to hear problems in a mix, like a stuffy mid-range or sibilant vocal, is easier than finding the specific frequencies causing it. A reliable technique is to dial in a significant gain boost with a high Q value and sweep through the spectrum. This exaggerated boost makes it easier to identify “hot” frequencies that are poking through.

Specific to iZotope EQs, you can also hit Alt/Option + Click on a node to solo only its frequency band when precise listening is required. Double-clicking problem areas after locating a problem will add a new node to the spot.

Isolate frequency bands in Neutron

As you sweep, some frequencies will react more than others—this indicates where the problem is. Reversing the gain control to taste to cut the offending frequencies.

Keep in mind, this solution works much better on static song elements than dynamic ones. A single EQ setting to remove low-end noise on a kick drum will suffice for the duration of a song because kicks don’t change much, but a vocal, on the other hand, has lots of variation from section to section and requires more edits.

In the second case, you are better off with a dynamic EQ which will follow a vocal and shift its corrective settings according to changes in audio content. When the problem surfaces, the EQ will work harder to tame it and relax when it isn’t there. This is also useful for other live instruments. Learn more about the dynamic Follow EQ in Nectar 3 below:

Shaping a tone: boost

After correcting issues with a signal, or if there were no issues to start with, the next step is to determine what there needs to be more of. Take a second to critically listen to the track in question—this gives you a sense of purpose when you EQ, rather than just cranking up gain for the sake of it.

Whereas corrective EQ employs narrow Q cuts, our ears are more sensitive to this setting when reversed as a boost, as shown above. At high gain levels, a narrow boost sounds unnatural and even painful. For this reason, wide, but gentle boosts are the default when enhancing a selection of frequencies.

When you’re new to production, it's hard to know how much of a boost is too much. Bumping up a kick with a lot of low-end makes it sound boomy, but if there’s not enough it will sound thin and struggle to carry the song. Increasing low-mid frequencies (around 150–350 Hz) makes a track sound warm and full, but this can easily spill over into muddy territory without caution.

Neutron EQ tip: holding shift while boosting or cutting (or moving left to right) will fix the frequency position (up and down or side to side) of your EQ selection so you can make more precise changes without affecting other parts of the signal.

If you regularly find yourself unsure of whether your EQ decisions are helping or hurting, use a tool like Tonal Balance Control to get visual feedback. Placed on the master channel, it will map the frequency content of your mix against a reference target in a real-time tonal balance evaluation. This allows you to dial into exactly where things have gone wrong. It may also very well be that your track is perfect, and you just have a tendency of over-working.

Pro Tip: hold alt/option and click to sweep across Tonal Balance Control to reveal which instrument might be causing an unpleasant build-up of energy.

Good tonal balance

If you already have a copy of Neutron, you can pull up any instance of it’s EQ in the Tonal Balance Control window to make adjustments on the fly. This way you get a sense of the big picture while still being able to surgically edit on the track level.

When in doubt: Track Assistant and Vocal Assistant

Both Neutron 2 and Nectar 3 have Assistant features that, much like Tonal Balance Control, help take the guesswork out of correcting and shaping instruments with EQ. After reading an incoming signal, the Assistant will offer up a unique mixing preset, including EQ, that can be further tweaked based on your own preferences.

This allows you to find which frequencies are causing a problem, as well as get a starting point for clear and cohesive mixes—all within a matter of seconds. Learn how this all works with vocals in Nectar 3:

Conclusion

You may have noted this article included a few technical tips related to actual EQ processes. A single instrument can include a series of small cuts and boosts to make it sound right for the song at hand and these moves differ from project to project—no one article can include all the possibilities.

We do, however, have many instrument-specific mixing guides across the iZotope blog and Youtube channel, which I encourage you to check out—for example: vocals, bass, guitars, and drums.    

Instead, use the tips here to create a game plan for the EQ tasks you face. Are you correcting an issue? Or looking to enhance certain feature? If you hit a wall and need some direction, tools like Tonal Balance Control and Track and Vocal Assistant are there to help.

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