Compressor Ratio Explained (Everything You Need To Know)
Compression is confusing.
And if you’re a home studio musician, producer, or engineer who’s struggling to wrap your head around it, you’re not alone.
But don’t worry, because in this article, we’re going to make things easier by zeroing in on one of the most important controls you’ll find on your compressor — the ratio knob.
First, we’ll talk about what ratio is in plain English (no geeky stuff). Then we’ll talk about the geeky math behind it. (Don’t worry — you can skip this section if you prefer.) And finally, we’ll talk about how to set your compressor’s ratio knob like a pro. I’ll even give you starting points for the most common instruments.
At the end of this article, you should feel 100% confident working with your compressor’s ratio knob in any mix.
But before we dive in, make sure you grab my free compression cheatsheet below. It’s packed with powerful tips and tricks that will help you approach compression with more clarity and confidence right away.
What Does The Compressor’s Ratio Knob Do?
To put it simply, a compressor’s ratio knob controls how aggressively the compressor clamps down on a sound.
Higher ratios cause the compressor to react aggressively. This will tightly control dynamics and dramatically reduce the difference in volume between the loudest and softest parts of the performance. Higher ratios tend to sound less transparent and more obviously processed.
Lower ratios are gentler. They cause the compressor to softly control a track’s dynamics. This effect will preserve more of the track’s natural peaks and valleys and lead to results that sound subtle and transparent. In fact, with lower ratios, you often can’t hear the compressor working at all.
Take a listen to the difference between high and low ratio compression on a drum kit:
Notice how much more aggressive the high ratio compression sounds. The low ratio compression is much more natural and transparent.
The Geeky Math Behind Ratio
Now that you know what ratio means in plain English, let’s talk about the math behind it. If you’d rather skip to the practical stuff, scroll down to the next section.
A compressor is nothing more than an automatic volume control. Whenever a sound gets louder than the compressor’s threshold, the compressor reacts by turning it down.
The ratio answers the question — for every dB the sound goes above the threshold, how many dB should the compressor let through?
Let’s say you set up a compressor with a 2:1 ratio.
This means that for every 2 dB the sound goes above the threshold, the compressor will only let 1 dB through.
If the threshold is set at -10 dB and the sound jumps up to -8 dB (2 dB above the threshold), the compressor will only let 1 dB through and the sound will end up at -9 dB.
If the sound goes above the threshold by 4 dB, only 2 dB will be let through and the sound will end up at -8 dB.
The higher the ratio, the more tightly the compressor will clamp down on the sound. If the ratio is high enough, the compressor may not let the sound go beyond the threshold at all.
For example, if the ratio is 100:1, the sound has to jump 100 dB above the threshold for the compressor to let just one measly dB through.
So for all intents and purposes, the sound can never get louder than the threshold. We call this form of compression brick-wall limiting, because the threshold becomes a “brick wall” and no sound is able to go beyond it.
How To Set Your Compressor’s Ratio Knob Like A Pro
Now that you understand what ratio is, let’s talk about how to set it on a practical level.
The first thing to realize is that all the controls on a compressor work together. Because of this, it’s best to adjust them in tandem instead of just focusing on the ratio knob in isolation.
When you’re tweaking your compressor, don’t solo the track you’re compressing. Instead, listen to the track in context with everything else in your mix playing.
This can feel difficult at first, as you won’t be able to hear the track you’re compressing as clearly. But by listening to everything together, you’ll be forced to make decisions that help the track you’re compressing fit with the other tracks in your mix.
When you’re compressing a track, it’s usually because the track sounds too dynamic. There is too big of a difference in volume between the loudest and quietest parts of the performance. This can make it difficult to find a static fader position for the track in your mix.
For example, if you set the fader on a vocal track to a good point in the verse, the track might suddenly sound too loud when the singer enters the chorus. When the chorus hits, you’ll feel like you want to turn the track down. But then the track will sound too quiet in the verses.
Compression can help even things out so the track sits consistently in the mix with one static fader position.
When you’re tweaking your compressor, keep this goal in mind. In most cases, your job is simply to set up the compressor so the different sections of the track sit evenly in the mix without needing to adjust the fader. There are certainly other uses for compression, but this is the primary one.
Set up your compressor with a medium attack and release time.
Set the ratio to a medium setting (3:1 is a good place to start).
Lower the threshold until you hear the compressor start to kick in.
Adjust the makeup gain until there is no difference in level when you flip the compressor in and out of bypass.
Adjust the threshold, ratio, and makeup gain controls in tandem until you feel like the track is sitting evenly in your mix.
If the track is too dynamic (you’re still hearing a big difference between the loudest and quietest parts of the performance), bump up the ratio and/or turn down the threshold. Higher ratios will result in a more processed, aggressive sound — which can work well on drums or tracks where you really want to hear the compressor working.
On the flip side, if you’re hearing the compressor kicking in and you want things to sound more natural and transparent, lower the ratio. The downside of lower ratios is that the dynamics won’t be controlled as tightly, which can make it more difficult to find a static fader position for the track in your mix.
Continue to adjust the ratio, threshold, and makeup gain until the track sits evenly in the mix without sounding like it’s being slammed with compression (unless, of course, that’s what you’re going for).
Ratio Starting Points For Common Instruments
I hesitated adding this section, because blindly copying settings and applying them to any plugin can often lead you in the wrong direction.
Every track is different, and the best approach is always to use your ears and determine the right ratio for each sound you work with. However, these guidelines can help get you started. Just be careful not to lean on them too heavily, as the “correct” settings will vary widely depending on your source material.
- For gentler vocals (folk, acoustic, jazz) — 2:1
- For more aggressive vocals (hip-hop, rock) — 4:1
- Drums — 2:1 for gentle level control that retains natural dynamics, 4:1 for tight control, 10:1 for a “slammed” drum effect (sounds great on parallel compression or drum room mics)
- Bass — 4:1
- Guitars — 3:1 for overall level control, or higher if you want to tame spiky peaks
- Keys — varies widely depending on what you’re working with
Wrapping Things Up
You should now know how to approach your compressor’s ratio knob in any mix. But if you’re ready to dive deeper, don’t forget to grab my free compressor cheatsheet below. It’s packed with additional tips and tricks that will help you approach compression with more clarity and confidence right away.
Before you go, what’s your go-to compressor plugin? Leave a comment below and let me know.