On Christmas morning, 1990, I received my first personal cassette player. It was a Sanyo BassXpander with AM/FM radio, auto-reverse and three glorious bands of EQ. I immediately set my nine year-old fingers to work mastering the use of this advanced tool with DC Talk’s “Nu Thang” as my source material. I discovered, naturally, that it sounded best with all three bands of equalization turned all the way up! I’m not sure when it clicked for me, but I eventually realized that I could achieve the same result by simply turning up the volume a bit. This new awareness opened the door to more subtle, artistic tailoring of the equalizer. I memorized different settings for at home vs. in the family van; for Christian Hip-Hop vs. Christian Hair Metal; for listening at low volumes vs. high volumes. This early introduction to equalization served me well when I started into live audio several years later.
EQ is essentially a volume control for a specific frequency. It allows you to tailor the sound of a source to make it fit well in the mix. These adjustments are a big part of the role of a sound engineer, as every source is unique. We make EQ adjustments to compensate for the way sources sound, for microphone placement, for the sound of microphones themselves and, most importantly, to help sources complement each other musically. EQ is one of the most artistic aspects of audio mixing and, like everything we do, it begins with listening.
First, let me be clear that this post is about channel EQ, found on the inputs of your sound console. Channel EQ is for tweaking sound sources and putting a mix together. It is adjusted musically, relying on your ears and artistic taste. Output EQ on the other hand, usually a graphic EQ, corrects for the sound of your speakers and your room. It’s adjusted more scientifically, usually with the assistance of audio analysis equipment.
Let’s take a look at the controls you’ll find in the EQ section of your console.
The channel EQs on the Allen & Heath mixers we use at our sites have blue knobs for bass, low-mid, high-mid and treble. You can add or remove up to 15dB in each band using these blue knobs.
The bass control affects everything below 80Hz and the treble control affects everything above 12kHz. These “everything past this point” controls are called shelving filters or, more commonly, a high shelf or low shelf.
The midrange controls, located in-between the two, are centred on a particular frequency and boost or cut it in a bell shape. These are called bell filters or band filters.
There’s another dimension to the band filters on most audio consoles, called sweep. An EQ with sweep controls is called semi-parametric. On an Allen & Heath console these are green knobs. A sweepable filter has an adjustable centre point – you can move it to pick out a particular frequency. On our consoles the green knob moves the frequency centre point and the blue knob boosts it or cuts it. It’s interesting to note the range of these controls too. A low-mid sweep control can be set lower than the low shelf! Similarly, the high-mid sweep control can be set higher than the high shelf!
On bigger analog desks and most digital consoles you’ll find fully-parametric EQ which offers one more dimension of control called width or Q. Q is the width of the band you’re affecting. A low Q value denotes a wider bandwidth which produces a smoother adjustment. A high Q value denotes a smaller bandwidth which can be useful for more “surgical” tweaks like cutting problem frequencies.
One more feature you’ll find on almost every console is a High-Pass Filter, labelled HPF. This one is a button, not a knob. The high-pass filter lets high frequencies pass, which basically means that it cuts low frequencies. It’s a shelf shape, but a much more drastic cut. It’s often set at the same frequency as the bass shelf but it’s a sweepable on some consoles. The high-pass filter should be enabled on every input except for bass sources like kick drum, bass guitar or some synths to filter out microphone handling noise and other unwanted sounds.
If you’re new to this it might seem like a lot to take in. My advice is to leave the sweep and Q controls at 12 o’clock and get used to cutting and boosting first. Once your ears learn to easily distinguish between bass, low-mid, high-mid and treble, you’re ready to start sweeping!
This week we talked about tools, next week we’ll look some techniques for getting the most out of your EQ.