EQ is one of the most commonly used signal processing tools in the studio today. Equalizers appears to be simple enough at first glance. I mean, we easily grasp the concept of how to use one. You simply boost or cut specific ranges of frequencies to make something sound better. But in case you were hoping for a more in depth explanation of some different ways to use EQ, here are a few basics and suggestions:

1. Subtractive

So the first two on my list are very basic concepts. Subtractive EQing is when you cut or reduce frequencies with your EQ. Some people prefer subtractive EQing. This is because if you don’t increase any frequencies, then you don’t risk clipping due to whatever changes you made with your EQ. There are even engineers that swear that this is the only way you should EQ, and you should never use additive EQ. It’s really a school of thought thing though, because there are also plenty of engineers that say it doesn’t matter as long as you know what you’re doing. Subtractive EQ is also great to use in conjunction with other techniques on this list!

2. Additive

Additive EQing is when you boost or increase frequencies in your EQ. I don’t think additive EQing is as bad as some people make it out to be, and here’s why: Back in the good old days, when the world was all analog, engineers had much more of a struggle with the signal-to-noise ratio. So back then, if you were to boost the signal through EQ, you risked substantially raising the noise floor, which can be a real problem for your recording. Nowadays, the noise floor is usually so low with all our digital and modern gear, that it isn’t such a huge concern. So, in my opinion, it’s okay to use a little of both additive and subtractive EQ. Just do whatever sounds best, make sure you watch for clipping, and you should be fine.

3. Noise Reduction

Have an annoying low hum in your vocal track? Struggling to get rid of a click somewhere in the chorus? Depending on the unwanted sound, and whether its frequency content overlaps the desired audio in the track, you can reduce or get rid of it with EQ.

With something like that annoying low hum, I like to engage a high pass filter on my EQ, and see if I can sweep it up so that it cuts the hum, but DOESN’T cut any of the frequencies in the vocal track. If you’re lucky, it might just do the trick. With something like a click, you can notch and sweep to find the click. I’ll generally select a band in a parametric EQ and set a very high “Q” value to it, so that I’m sweeping in a very small range of frequencies. Then I’ll highlight and play the offensive section on repeat, sweeping the band in my EQ around until I find the location of the click. Sometimes I’ll do this by boosting the band, and listening for a boost in the offensive sound. Sometimes I’ll cut the band instead, and sweep back and forth on the frequency axis to listen for when it retreats. Either way works. Again, if you’re lucky, the frequency content of the offending sound won’t overlap with your desired audio, and you can safely remove it. You’re also lucky if the frequency content of the offending sound exists in such a small range of frequencies that you can cut it without reducing the quality of your desired audio. The key here is to listen to what you’re doing, and be careful. There are other ways of reducing unwanted sounds if EQ doesn’t cut it.

4. Harmonic Work

Do you ever notice that some vocalists simply have some very grating frequencies in their voice? It’s not their fault by any means, and they can be an amazing vocalist and still have this. Actually, every instrument has harmonic frequencies that exist above the fundamental frequency. The fundamental frequency gives us the pitch or note that we hear when the instrument is played, but the harmonics are what really give the instrument its characteristic sound. They’re essential, and important, and you generally shouldn’t cut them. However, sometimes you’ll hear some pesky or annoying frequencies – especially with vocals. Luckily, you can reduce those using EQ!

To do this, I actually use a very similar method to the one used for the click sound above. I usually pick a band in a parametric EQ, and set a high Q value. I then boost that band dramatically, and sweep it up and down the frequency spectrum to listen for the ugly harmonics. When I find them, I simply cut that range, adjusting the Q and how much I cut it based on how things sound.

Another type of harmonic work that you can do with EQ is finding and either boosting or reducing the fundamental frequency. Select a band, and sweep it around like I described above to find the fundamental. Then adjust accordingly. There are some great EQ plugins that will visually display where the sound is falling on the frequency spectrum. If you’re a beginner and still developing your ear, this can really increase your speed in finding something like the fundamental. I also think it’s good for ear training to have a visual reinforcement of what you’re hearing.

Anyway, this technique can be especially useful for something like a kick drum. Once you find the fundamental, you can either boost the fundamental for a bit more power, or reduce it for more of the upper “snap” of the drum. For more information on that, visit this post, where I went over using EQ on a kick drum in a bit more detail.

5. Make Room in the Frequency Spectrum

This is probably my favorite use for subtractive EQ. Once you get into mixing a track, you might struggle with a muddy, busy, or “out of control” sounding mix. An easy way to clear up some of the jumble is to free up space in the frequency spectrum. You do this by observing an instrument (let’s say voice for this example), and assigning it a “space” in the frequency spectrum. Then, reduce or cut that same frequency range in other instruments in your mix. I mean, obviously you don’t want to cut anything essential, so use your ears and best judgement. Think of it as cleaning up some junk in the other instruments, so that your vocals can shine through where they are strong.

This technique is great because it really helps an instrument pop out in the mix. If you just try to boost the element that you want to stand out, then you’re just adding more noise to the jumble. But cleaning up everything else and making way for the desired element can reduce the muddiness and give you the sound you want.

6. Graphic EQ and Rounding Out your Track

The most commonly found EQ plugin is a parametric EQ. Like the stock EQ in Pro Tools, parametric EQs allow control over the width (or “Q”) of the sections of frequency that you boost or cut. Graphic EQ units, however, are more common in high end home audio, and in live sound. You can boost or cut audio with these EQ units using equally spaced chunks of frequency (usually octaves). These frequency bands often overlap each other slightly. These units usually look like a row of faders, with each fader controlling a frequency band. While you don’t necessarily have as much precision with a graphic EQ, they can be great for rounding out the frequency balance in your mix.

Give the mastering engineer a head start! Find a graphic EQ (or even use a parametric EQ with low Q settings on the bands for a similar effect), place it on your master fader, and adjust the frequencies to improve your overall mix. Try boosting the upper-mid frequencies, and listen to see if it adds that extra definition that you wanted. Give the lows a small boost for a bit more power. Experiment and hear what works for your track.

Questions? Comments? As always, please share in the comments below!