Continuing our series of EQ Tutorials, we’re taking a closer look at the subtractive EQ technique and how it can help you take your mixes to the next level.
“Subtractive EQ” essentially means using an equalizer to attenuate the volume of a certain frequency range. This is also known as a “cut”, as opposed to a “boost” which is also referred to as “additive EQ”. To avoid confusion, do note that you can “cut” or “boost” with pretty much any equalizer plugin. Load your go-to EQ plugin and reduce the volume on any of its bands – that’s a “cut”. Doing the opposite will result in a “boost”. Voila!
Removing Unwanted Frequencies
One of the main goals for using the subtractive EQ technique, aka using your equalizer for cutting, is to improve the overall sound of your mix by removing unwanted frequencies in individual tracks. This will result in a cleaner mix which will sound more crisp, better defined, and less muddy. It also helps us bring out the natural sound of a particular element of the mix, be it a vocal, a synthesizer, or anything else.
Let’s take a violin recording as an example. It normally shouldn’t contain any extremely low frequencies so it would be safe to cut the bass region to remove any unwanted background noise or hum that was captured during the performance. The same would apply for any resonances that might appear as the result of non-ideal recording conditions, lower quality recording equipment, or simply as part of the performance.
With practice, you will become able to detect these unwanted frequencies by ear and remove them accordingly. For now, you can create a slight boost in your EQ and scan the entire frequency range to find any nasty sounding noises which can then be removed with a cut. We will focus more on this particular technique in a future video.
Preserving Headroom
Another reason why subtractive EQ is such a common technique is that it helps us prevent clipping in the master channel. By removing frequencies, you are also saving headroom and leaving space for other elements in the mix. As mentioned in our introduction to equalizers, each EQ band is essentially a volume fader for a particular frequency range. By boosting a bunch of frequency ranges in different tracks across your mix, you are actually increasing the volume of those tracks, which can potentially result in clipping.
As an experiment, load one of your projects and take note of the highest peak volume on the master track as it’s playing. Now try to mix that same project by only using “boosts” instead of “cuts”. If you play the entire song again, you’ll notice that the maximum peak volume is now much higher, perhaps even clipping and resulting in that crackling sound nobody wants to hear. This won’t happen if you mainly focus on subtractive EQ while mixing.
Summary
With subtractive EQ, we have two main goals. We are removing unwanted frequencies in order to:
- Bring out the natural quality of the recordings in our mix.
- Preserve the headroom in our mix.
As mentioned before, you can do this with pretty much any equalizer plugin on the market. In the beginning, you should focus on using the stock equalizer that comes with your DAW, or a good freeware one like SonEQ or SlickEQ. And speaking of free equalizers, Eventide just released a new plugin called EQuivocate ($99 value) which can be downloaded free of charge until October 31st.
