I’ve talked at length about the best practices when using EQ here on Music Guy Mixing. Most notably I put together a complete EQ cheat sheet to cover exactly how to best EQ the most common instruments in your mix. One of the EQ settings which doesn’t get as much coverage is the slope EQ setting. Let’s talk about slope EQ, what it is, how it affects what you’re EQing, and where to set this.
Slope EQ
Let’s begin by identifying what the slope setting even is as it relates to EQ.
What is Slope EQ
The slope EQ setting dictates how steep the grade of your EQ band is. Measured in decibels per octave, a higher number means that it goes up that many decibels per frequency octave jump.
It’s typically measured in multiples of 6dB or 12dB and the higher the number the sharper the grade of the slope.
For instance and as you can see above, 12dB/oct is on the low end and creates a smooth, gradual, and natural slope.
Conversely and on the high end, 96dB/oct is a steep and sharp incline.
As you can also see, the lower the slope, the more surrounding frequencies will be affected.
Conversely once again, the higher the slope, the less surrounding frequencies will be affected because the change happens much faster over a shorter frequency (Hz) distance.
Slope Vs Q
It’s easy to mistake slope for another EQ setting, the Q setting, because from a distance it appears that they BOTH affect the grade of the curve for an EQ band.
The difference is that the Q setting affects the width or range which an EQ band occupies:
A smaller Q results in a wider band, meaning more of the surrounding frequencies will be affected. A higher Q results in a narrower band, meaning less of the surrounding frequencies will be affected.
This image demonstrates what a gentle and aggressive/sharp slope looks like when applied to the same default Q setting:
As you can see, the slope makes that transition a lot faster, thereby leaving more of the surrounding frequencies untouched. While narrowing the Q does a similar thing, both settings create a similar effect from different angles.
What Slope to Use With EQ
This begs the question, what slope should you use when setting up your EQ?
As I mentioned in the initial graphic, a gentler and lower slope results in a more natural and transparent sound.
Go too aggressive with any of the settings on an EQ like having too steep a change between frequencies and you open the door to potential phase issues in your audio.
As such, the best slope to use whenever possible is 12dB/oct for the most any kind of filter you create.
Occasionally I’ll employ a 24dB/oct or even more rarely a 36dB/oct slope when using high and low pass filters. This achieves a cleaner cut, sacrificing less of the audio I want at the frequency point, while filtering out the frequencies I don’t want.
Another rare exception for when you can go higher is when you need to do some surgical cutting to filter out a specific and small frequency range while preserving the surrounding frequencies. You’d also use a higher Q in this situation alongside the greater slope.
Just remember that less is typically more when it comes to EQ in general.
Gentler, wider, and smaller boosts/cuts will result in a more natural and transparent sound which should always be the goal.