How to use parametric EQ

A parametric EQ is the most important audio plugin that a home recording engineer can use.

Why?

It is a powerful tool that helps us to get a decent sound.

How EQ works (in general)

There is another kind of EQ called a graphic EQ. It focuses on the same adjustments, but "sees" them in a different way.

All sound is made up of frequencies, or vibrations. Frequency means how fast the sound waves are vibrating - a person can hear from around 20/40 hertz (vibrations per second) all the way to around 20,000 hertz (also known as 20 kilohertz). In some amazing way, sounds of all shapes and sizes combine together to give our ears a treat.

Any instrument or voice you can record will utilize certain of these frequencies in the sound. But sometimes the capture process (recording them) doesn’t give an ideal representation.

That’s where EQ steps in, to equalize things and make it sound better. How? By adjusting selected portions of the entire spectrum. If some frequencies are too high, cut them a bit. If others are too low, boost them.

There are any number of reasons why it is not perfect the first time, but most are technical, and we don’t need to get into that here.

See this page on EQ for a little more background.

Parametric EQ

Parametric EQ is a fancy way of naming a useful way of implementing EQ. For comparison, the other kind is a graphic EQ.

Parametric EQ
Graphic EQ

They both work with frequencies, and they both boost or cut at specific levels. The difference is in customizing - a graphic EQ has sliders for specific frequencies, but they can’t be changed. A parametric EQ has knobs instead of sliders. The knobs allow you to dial in a precise frequency, called the band.

So here’s a detailed look at parametric EQ controls.

  • frequency
  • width or Q
  • gain

Frequency

A parametric EQ allows you to specify the center point for frequencies affected by this band (remember, band is this particular adjustment).

This is the control that you will probably spend the most time working with, because it is more important than the other controls.

Why? It matters more what frequencies you adjust (highs, lows, mids, mid-lows, etc) than it does how much you cut/boost, or how wide the band is. This does not mean the other controls are not important, they are just less important.

The frequency control should be the first parametric EQ control you study.

Width or Q

The frequency knob sets the center point for what frequencies are affected by this band, and the width sets how much on each side are affected.

Look at the pictures to clarify.

Parametric EQ with a wide Q
Parametric EQ with a narrow Q

The first one is using a wide Q setting so that it affects many surrounding frequencies. The second picture shows a narrow band, that just cuts a few.

What is a good setting to keep this at?

Use your ears as a judge. Once you find the problem frequency (see Find the Frequency), cut some narrow before going wider. I don’t have a set value that I use, it just depends on what needs to be done.

Gain

The simplest parametric EQ control. Yay!

Once you have the other two controls set on a band of EQ plugin, just dial in the gain to where it does the most good.

But be careful, even here. This is where many beginners go wrong - they try to cut the living daylights out of a problem range, or boost way to much on a missing area.

Somewhere in my recording education, I learned a really good principle for EQ. When you do an EQ adjustment, use half the gain than what you would like to. In other words, if you think a cut at 1400 with a width of 1.2 and a cut of 8db makes things better, try making the cut 4db. Come back to it later and see if it sounds good, or if it really needs the 8db cut.

Shapes

Yes, parametric EQ has a shape!

Each band of EQ is a certain shape. They usually fall into one of 5 categories:

  • bell
  • high pass
  • low pass
  • high shelf
  • low shelf

The difference is in what shape they interact with the sound spectrum.

Parametric EQ with available filters

Recall the pictures above where each band operated on a shape similar to a bell curve - equal on both sides. It drops off from the middle, how soon depends on the Q or width setting.

The bell filter is what you will usually use a parametric EQ for.

The high pass filter is useful for limiting the amount of bass frequencies in a track. The human ear can only hear down to about 20 hertz (a good one), so it doesn’t make sense to include sounds lower than that. Not only that, but it saves the speakers from having to try to make those high energy sounds.

The solution is the high pass filter. It does what you would think - only lets through frequencies that are higher than a certain point. So if you put a 40 hertz high pass on a band of EQ, anything lower than 40 is taken out, while the rest is untouched.

Even though our ears can hear down to 20 hertz, most instruments don’t even use the range between 20 and 60 hertz. I find no discernable difference when I use a 60 hertz high pass filter on choral music. The lower notes on a bass guitar are down in that range, but most instruments don’t need it (and sound better without that clouding up the rest of the mix).

A low pass does the same for high frequencies - it cuts anything above the threshold point. It is less useful than a high pass. At least that’s how I’ve found it.

Don’t let the two names mix you up - high pass operates on low frequencies, and low pass operates on high frequencies.

A low shelf filter is close to a high pass. Instead of just cutting everything that is lower than the threshold, you can set a specific level of gain or boost. In other words, you could set a low shelf filter to boost all frequencies lower than 400 hertz (and then have a high pass to cut anything lower than 60).

Parametric EQ with a high pass and a low shelf
The most important tip for parametric EQ that I can leave with you is experiment.

As you could guess, the high shelf is the opposite of the low shelf, and boosts or cuts all frequencies higher than the threshold.

Visualizer

Most parametric EQs show you visually what your adjustments look like. This is in the form of a line from left to right across a “sound spectrum,” from low to high frequencies. When you boost or cut, it shows the visual details of that cut so you can see how much you are doing.

Parametric EQ - tips and techniques

In my years of working with audio, I’ve found a few techniques that work really well for making good use of a parametric EQ. Keep in mind - these are not magic bullets, but helpful starting points or techniques that will help you get started quickly.

Small adjustments

I mentioned this before, but it stands to be mentioned again. Don’t do too much! Many times I’ve spent long periods of time working with a track or mix, trying to get the EQ right. But at the end, I just didn’t like it. In that case, I took all the EQ off and started from scratch.

Every time I did this, I remembered that it just doesn’t pay to try to do too much. Don’t make it complicated. Make EQ as simple as you can, and it will probably sound better.

Find the frequency

I’ve lost count of how many times I use this technique - pretty much all the time.

It’s simple - if you hear something that is not right, find the offending frequency. Start by taking a narrow Q and a lot of gain, and “sweep” up and down the spectrum.

The narrow width helps you find the exact spot, and the gain amplifies the problem when you sweep over it. During your sweeps, listen for the places where the problem jumps out. Find the middle of that section, and set the frequency control to that.

Now all you have to do is reset the Q and gain to best take care of the problem.

It’s a simple thing, really, but incredibly powerful.

Try a different Q

Sometimes when I’m using the “Find the frequency” technique, I end up with a bunch of small adjustments that address small problems, but I still have a fundamental problem.

In these cases, it’s probably my Q settings that need work. Maybe instead of cutting in three small areas, I need to use one band to cut the same area, but with a wide setting.

The most important thing

A parametric EQ is a powerful tool that will help you achieve that elusive good sound in your mixes. But only if you use it correctly.

I wish I had a cure all solution, or a set of presets for an EQ plugin. That would make it easier for all of us.

But part of the magic about mixing is the process to that sound.

Please experiment with EQ. try things this way, and try them that way. Spend time with the Find the Frequency technique. Discover how boosts and cuts sound in various frequencies across the spectrum.

The most important tip for parametric EQ that I can leave with you is experiment.

Sorry to disappoint, but I don’t know any other ways. Sure, read the books. Learn all you can about EQ and digital recording.

But all of that theory won’t do you any good until you have some cold, hard experience with EQ.

Let me know how it goes.

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