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How to EQ Instruments

When equalizing instruments, we need to consider how they interact with one another - a good place to start is determining if multiple instruments have fundamentals that overlap. If so, it is likely a good idea to attenuate that fundamental on one or more instruments to create spectral balance.

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Understanding Fundamental and Overtones

The fundamental is an instrument’s lowest note - which can be observed on an EQ by the lowest spike. Sometimes we have signal below the fundamental, but this is often rumble picked up in the room, hum, or some other noise unrelated to the musical aspect of the signal.

Overtones, or harmonics, are multiples of the fundamental and are always tied to the fundamental - meaning if the fundamental changes, the harmonics change.

So if the fundamental is 100Hz, harmonics would be 200Hz, 300Hz, 400Hz, and so on. I start with this info since it’s very important to understand when equalizing any musical signal.

Let’s listen to the fundamental of a signal, and then slowly introduce harmonics.

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Why Low Frequencies are Difficult to Mix

Another bit of info that’s helpful to know before equalizing, is how the low-frequency range presents a unique set of issues. If we look at a scale in the low frequencies, we’ll notice the notes are much closer together than in the high frequencies.

Additionally, low frequencies are often very powerful - since they’re harder for us to hear, mixes need more lows to sound balanced. So let’s quickly listen to the lows of a mix, and notice how clustered the range can quickly become if EQed incorrectly.

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Separating Kick and Bass with EQ

Following the ideas from the last chapter, let’s consider how to separate our kick and bass - first I want to find the fundamental frequency of the kick. What’s great about the kick is that it stays just about the same frequency meaning, I can attenuate its fundamental on my bass.

I’ll dip the frequency about 3 to 5dB - resulting in more space for the kick, and less clashing in the lows.

Let’s take a listen.

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Important Frequencies for Synth and Guitar

On synth and guitars, we’ll want to leave the fundamental in if the instrument is used to fill the spectrum, but if it’s competing with the lows of the vocal, or making the mix clutter let’s attenuate it. To keep it from covering the vocals we could attenuate a little of 250Hz, and 2kHz.

Or we could boost these if the vocal is sticking out too much. Lastly, if we have a mid-side EQ, I’ve found that amplifying the side image around 300Hz almost always improves the sound of these types of instruments.

Let’s listen to some of these filters and keep in mind how the instrument interacts with the vocal, and how amplifying the side image lows improves the sound.

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Important Vocal Frequencies

I know we’re talking about instruments, not vocals, but in case you want to mix BGVs or consider how instruments interact with your lead, let’s look at the important ranges. First, we have the fundamental of course, which contains the majority of the vocal’s power.

500Hz is where we’ll find vowel pronunciation - pull this back to make the vocal sit back, and push it forward to bring the vocalist closer to the listener.

800Hz to 1.3kHz can contain nasally tones, so if the vocals sound nasally you should dip these. You can boost 2-5kHz to help the vocal cut through, or attenuate it to help it sit in the mix.

Lastly, we have sibilance at 5 to 10kHz, which we’ll want to dip a good amount on BGVs, and the air above 12kHz.

Let’s listen to a vocal with these areas affected, and consider how it changes the balance between it and the rest of the mix.

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Mid-Side EQ on Drum Bus

Let’s introduce mid-side EQ on the drum bus - we’ll find the kick’s fundamental and on the mid image amplify, as well as amplify the snares fundamental which should be around 2kHz. Then let’s boost the mids on the side image, and more importantly, the highs with the high shelf.

If we want the snare to cut through more, let’s amplify roughly 3kHz on the mid-channel. Also, if we want the kick to be more focused, we can make it mono with a high-pass filter on the side image. Let’s take a listen to how this augments the drums.

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Equalizing Orchestral Instruments

Typically orchestral instruments should only be treated with very gradual curves - for example, if you need to introduce a high-pass filter make it 6dB per octave. Or if you need more high frequencies use a high bandwidth shelf and amplify only about 1 to 1.5dB to keep it natural.

Although cutting the side’s lows works well on a kick drum, that shouldn’t be done on orchestra basses. Let’s take a listen.

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Accenting Key with EQ

Knowing the key of the song we’re mixing helps a lot - once we know that, we know the 7 in key notes and the 5 out of key notes. These notes can be converted into frequencies that we can amplify if they’re in-key or attenuate if they’re out of key.

So let’s apply some equalization to the full mix using this info, and consider how you could you this to make your mixes more musical.

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Softening Instrument with Linear Phase

If you have an instrument that’s sounding too harsh, or maybe you just want it to be slightly subdued sounding, enable linear phase on your EQ. This will cause mild phase cancellation, and the effect will become more noticeable the higher the latency you select.

I find this works great on vocals, but let’s try it on drums since that’ll make the effect clearer - that said, I wouldn’t recommend this effect on drums in most cases.

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Stereo Widening on Instrument with EQ

We touched on mid-side EQ, but let’s look at how it can both control the spectrum and widen your stereo image. Let’s say we add reverb to a signal, and want the reverb to be more impressive - we can add an EQ after the reverb and amplify aspects of the side image.

So let’s amplify the highs on the side, and the mids, and take a listen to how it widens the instrument and improves the reverb.

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Inverse EQ Competing Signals

If 2 signals are really in each other’s way, we can use inverse EQ to help - first match one of the signals to the other using an EQ with a match function. Then, after deleting extreme bands, highlight the ones that remain, and invert the gain value.

Now everything that would’ve made them match is causing separation between them. Let’s take a listen to this effect.

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