Frequency equalization (often abbreviated to EQ) is the method of shaping an audio source through the attenuation or addition of certain frequencies. While it is one of the most powerful and important tools in an audio engineer’s arsenal, it is also quite enigmatic in the sense that newer producers don’t quite understand exactly what it should be used for, and how it should go about doing the difficult task of cleaning up your mix.
An Introduction to Sound
Every sound we’ve ever heard, and ever will hear, arrives at our ears in the form of vibrations in the air (sound waves). These waves vary in tiny amounts to create very different sounds, and are translated by our brain into something we can process and understand.
These sounds fill up a metaphoric box of frequencies, ranging from around 20 to over 20,000 Hertz (Hz). Audio engineers use equalization as a means to reduce or increase specific frequencies of a particular sound in order to build to it, or make it sit clearer in a mix. These frequencies are often split into three or five bands; lows, mids and highs, or bass, mid-range and treble.
Your Ears and Eyes
It’s important to note that there is more than one way to read an audio signal. While most traditional engineers will tell you to use your ears not your eyes, there are definitely specific results in spectrum analysis that some people simply won’t achieve by listening. Especially if their ears aren’t as developed as, say, a mastering engineer with 15 years of experience.
This is where spectrum analysis comes into play. Spectrum analysis is a visual representation of the frequencies of an audio signal. It is basically a graph telling you what you need to cut out of a sound, and what you might need to add.
Many EQ VSTs include simple spectrum graphs to read the information, but there are also more advanced hardware variants that include things like phasing and stereo imaging. But that’s a story for another day!
Before we begin actually shaping any sounds, we must first understand which frequencies the sounds need, and which ones they don’t. As a general rule, it’s best to not add frequencies to a sound, but rather take frequencies away from other sounds in order to clarify the mix (instead of making it clip or sound muddied).
For example, if we want our kick drum to sit nicely in the mix, with a good amount of bass and a punchy high-end, we would want to subtract other sounds away from where we want our kick to sit. This may involve rolling off the low-end of other sounds (such as a guitar or vocal line), and creating a notch where the click is hitting.
Here I’m using a kick drum, snare drum, bass synth, a crash and some hats. Let’s listen without EQ first. You can’t really hear the kick or snare clearly, and the bottom end sounds muddy and unprofessional.
Let’s fix this. Open up an EQ on each of our channels, I’m using Ableton Live’s native graphic equalizer. I’ve also loaded a spectrum after the EQ (the order of FX is important!) to read the graphic information. It’s a very good habit to have a second perspective on things.
To display the frequency of a sound, simply hit Play and watch your spectrum display. As you can see, the display shows that our bass synthesizer is heavy in similar frequency ranges as our kick and snare drums.
To fix this, we’ll take some of the clay off. There are several types of EQ bands, these include notch, low pass / high cut, high pass / low cut and shelf. Each has its own place in equalization, and we’ll look at each in depth.
First we’ll use a low shelf on the bass to reduce the bottom end a bit. Around -3 dB should do. Next, we’ll take a notch to where the snare is most prominent, often it lies around 250-300 Hz.
When it comes to notches, the sharper the notch, the larger the gain change you can apply. This can be useful for taking out extreme harmonics (such as unwanted resonance on a snare drum).
With our bass sorted, it’s time to make our snare drum punch through the mix. There are several ways to achieve this.
My personal favourite involves rolling off the low end and dipping the mids, while slightly boosting the primary frequencies of the snare to give it a lot of body and taking away unwanted frequencies.
Next, we’ll take some of the mid-range away from our kick drum and roll off any unwanted high-end. This gives us room to add things like vocals or guitars without taking any power away from our kicks.
Finally, we’ll roll of all the low end on our hats and cymbals by using a high-pass filter, because these high-frequency sounds can be heard at such low levels, we can take away a lot of the unwanted frequencies without worrying about them being lost in the mix.
In addition, if your mid frequencies are muddy, there’s a good chance that there are renegade frequencies ruining your potential masterpiece by hiding away in your overheads.
One more thing to note, is that some EQs incorporate a mono/stereo feature, such as Ableton Live’s native equalizer. This allows frequencies that you haven’t panned to remain untouched, while you cut out the sides.
While quite advanced, using this properly allows you to remove things like high-hats from already finished tracks in order to remix/bootleg them.
By using solely EQ and some basic knowledge on sound design, we’ve changed the muddy mess of this:
To a much clearer, more defined mix:
Hopefully this has shed some light on one of (if not the) most important mixing tool at your disposal. Now it’s time to ruin your track with some DIY mastering! Go on, get to it!