May Plugin Sales >>From $5<<

What Is Ratio In Compression? (Explained With Sound Examples)

Master your understanding of compression settings:

Quick guides to compression settings for instruments:

Compression ratio is the level of gain reduction that takes place in relation to the input signal. The higher the ratio the more compression that takes place.

What Is Compression Ratio?

The compression ratio dictates how much of the outputted signal is reduced. With a ratio of 2:1 for instance, every 2 dB that passes the threshold level is reduced by 1dB. Further to that, if 8dB passes the threshold then only 4 dB is output.

compressor ratio
Ableton compressor with Ratio highlighted

Getting the right ratio is crucial for creating natural dynamics. If for instance you’re placing a compressor on a mix bus you may want the ratio set low in order to gently squeeze the transients without squashing the mix.

On the other hand higher ratios are great for guitars and vocals where you want to close the gap between the loudest and quietest parts and create a wall of sound.

How Does The Ratio Knob on A Compressor Work?

High compression ratios achieve more compression, while lower ratios output a signal with less compression. Neither of this would be possible without a knob that controls the threshold level. The threshold is the volume which the signal must exceed before compression kicks in.

For instance, if the compressor’s threshold is set to -10 dB then anything that passes this volume will be compressed at the rate determined by the ratio knob.

Essentially the ratio and threshold knobs cannot complete their functions without the other.

Ratio Levels Explained:

  • 1:1 ratio – no compression takes place
  • 2:1 ratio – every 2 dB past the threshold is reduced by 1 dB. Accordingly, 10 dB is reduced by 5 dB.
  • 4:1 ratio – every 4 dB is compressed to 1 dB, 8 dB down to 2 db, and 16 dB to 4 dB.
  • 10:1 ratio – 10 dB is compressed to 1 dB, 20 dB down to 2 Db. Very extreme levels of volume attenuation.

How Does Knee Affect The Ratio During Compression?

The knee setting dictates how aggressively the input signal triggers the compressor. A soft knee will gradually ease the compression in before the threshold is reached, making it sound more well rounded and natural.

Visually it will have a rounded edge:

4d8f4ce1 5ee3 474f 9aa4 e47323de25f8

Essentially the compression will kick in a little before the threshold and the full ratio won’t be applied until a little after the threshold.

A hard knee will instantly compress as soon as the threshold is exceeded. It will look more severe:

919bf60d ff21 4933 b16d 79b294f8905e

The compression doesn’t kick in until the threshold is reached, and full compression will occur at the point of the threshold.

Not all compressors have a knee parameter, so don’t be surprised if your favourite compression hardware is missing this particular knob.

Compressors with the knee function will either allow you to choose between a hard knee or a soft knee, or dial in a decibel level so you can find a blend of hard and soft of your choosing. 0 dB is a hard knee and any value above 0 starts softening the knee.

As a rule of thumb hard knees are suited for fast moving transients. Hi-hats, hip hop beats, lead guitar riffs and fast paced vocals all benefit form a hard knee.

Softer transients such as rhythm guitar, piano, and synth pads require a softer knee.

Sound Examples

For reference, here is a drum beat with a soft knee:

Drums – soft knee

And here is a drum kit with a hard knee:

Drums – hard knee

What Is The Maths Behind Compression Ratio?

The maths behind ratio compression is quite simple.

  • 2:1 ratio compression will reduce everything by half:
    • 2db reduced to 1db
    • 6 db to 3 dB,
    • 10 dB to 5 dB
    • …and so on.
  • 3:1 will reduce the outgoing signal to a third
    • 3 dB reduced to 1dB
    • 6 dB to 2dB
    • 9 dB to 3 dB
  • 4:1 will reduce the output signal to a quarter
    • 4 dB reduced to 1dB
    • 8 dB to 2 dB
    • 12 dB to 3 dB

Sound Examples

For reference, here is a drum beat with a 2:1 ratio:

Drums – 2-1 Ratio

And here is a drum kit with a 10:1 ratio:

Drums – 10-1 ratio

Tips For Setting Compression Ratio

The compression ratio is not just linked to the threshold, but also to your intention.

  1. Do you wish to sidechain your bass to the kick drum? Then it’s best for a inf:1 setting as the point of sidechaining your bass to the kick is to scoop out the initial hit of the bass frequencies to allow the kick to shine through.
  2. If you are simply taming transients on a mix bus, say for instance on a drum kit, then a ratio of 4:1 or 2:1 is preferable. The effect will be subtle as the output level won’t be so aggressively attenuated.
  3. Are your guitars sounding lifeless in parts and getting drowned by the track’s dynamics? Whack the ratio up to 10:1, with a slow attack that let’s the initial twang of your riffs through. Set a medium to slow release time (adjust to taste) to will create a wall of sound that brings your guitars front and centre. Then finally, pan off to the sides.

How To Set compression Ratio Perfect Every Time

Since the ratio affects how much your audio will be compressed, it’s worth testing out what different ratios sound like. Here is an example of a 2:1 ratio on a master bus:

2:1 ratio on a master bus

As you can hear, the compression is subtle and natural sounding.

Let’s increase things to 4:1.

4:1 ratio on a master bus

This still sounds ok but the guitar is becoming a bit more prominent in the mix at the expense of the drums.

Now let’s whack it up to 10:1.

10:1 ratio on a master bus

As you can see, the glued sound of the 2:1 ratio has been lost and now we are starting to hear audible distortion from too much compression. It’s a good idea to start at this level and dial it back until it begins sounding more natural.

A Brief Overview of Compression Settings

Here’s a quick overview of all the compressor settings:

  • Attack & Release – attack time is how fast the compression occurs, dictated in milliseconds or seconds, and release time is how long it takes to relinquish the compression.
  • Makeup Gain – after the the compressor does its thing you can then increase the overall volume using the makeup gain
  • Ratio – how much gain reduction is applied once the signal passes the threshold.
  • Threshold – the volume the signal must pass before compressor kicks in.
  • Dry/Wet – also known as ‘Mix’, this option lets you blend the dry and wet signal (with compression and without compression) in order to achieve a more natural sounding output.

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top