Understanding Compression (Audio Compression For Dummies)

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  • Learn the basics of dynamic range compression
  • Find out how is sculpts your sound
  • Use this cheat sheet to get you started on compression

What Does Compression Do?

If you’re new to audio production you’ve probably heard all about compression but you may be a bit unsure on how to approach it in your mixes.

Compression, or ‘dynamic range compression’ is a fairly straightforward concept but it is important to know how (and why) you would use it in audio production.

Compression, in its conventional usage, causes the louder parts of your audio signal to be reduced in volume. Think of it as a way to balance out your recordings by creating a smaller range in volume.  

The great thing about compression is that while it does reduce gain, it has the ability to keep the timbre of the recording the same (although some compression units will add their own unique coloring).

Compression can be used subtly to tame audio or instead used heavily to create ‘louder’ and punchier sounds. You can also use compression as a creative effect, and even as a distortion/clipper when used in extreme ways.

All in all, it’s an incredibly versatile tool that every producer should get to grips with.

Remember any time you use compression you are reducing the dynamic range of your sound which can make or break a mix!

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What Is Dynamic Range?

Dynamic range simply refers to the difference between the loudest and quietest parts of your audio. The higher the compression the less the dynamic range.

It is an extremely important part of mixing and mastering. As a general rule a good track will have balanced dynamics and this is important to remember when applying compression.

More dynamics create more effective mixes. We’ve all seen horror movies where a softly spoken scene is interrupted with a loud jump scare from a ghost or monster. But when the speaking is the same volume as the monster, it lacks impact. The same principle can be applied to music.

When Should I Compress?

The honest answer is there is no right or wrong! However there are some theories that apply as a ‘rule’ to audio mixing.

Audio engineers will tell you to use your ears and only compress a track when needed, which is great if you’re an experienced mixer but if you’re new to production you may be in the dark about when to compress.

A great tip if you are a beginner is to try compression on everything.

Tweak the parameters to the extreme and see if you can tell the difference. A/B’ing, or comparing your uncompressed and your compressed signal, is a great way to learn.

There are a few pitfalls with compression however. It is common for vocals to be compressed but applying too much can create unpleasant sibilance (or emphasised ‘sss’ and ‘t’ sounds). Compression is a great way of adding punch and aggression to your drums, but setting a fast attack time can negatively effect the sound by ‘choking’ the drum hits and destroying transients.

How Do I Compress?

Open up your compressor plugin (check out these 5 free compressor VSTs here) and you might be confused by the parameters and controls. The first thing you need to do is set at what point the compressor will start working.

This is what the threshold control is for. The threshold relates to loudness, or more specifically how loud your signal has to go before the compressor kicks in, and it is typically expressed in decibels (dB).

A simple way of doing this is looping your track, and reducing the threshold until you hear or see the compressor begin to work. Typically you will see either a needle or meter start to move when the compression begins. The amount the needle or meter moves is directly related to the gain reduction, or how much the volume is being reduced by.

The lower the threshold, the more compression you can generally add as there will be more signal passing the threshold point. Let’s give it a numerical value – say your threshold is set at 5dB, and your signal reaches 10dB, then that means you can reduce the signal by up to 5dB. If the signal reaches 12dB then you can reduce it by up to 7dB.

To change exactly how the signal is reduced after crossing the threshold, we’ll need to look at the other controls on our compressor.

anatomy of a compressor

Ratio

This relates to how much compression is actually applied. You will usually see this in the format of 2:1, 4:1, 10:1 and so on. This can be a little confusing but is actually very simple, a 2:1 ratio means for every 2dB the signal passes the threshold it will be reduced to 1dB. This would also mean for every 4dB past the threshold the signal will be reduced to 2dB.

The higher the number the higher the amount of compression. Limiters, which are a type of compressor, use high ratios to ‘brickwall’ the sound.

Threshold

The threshold determines the level at which the compression effect will kick in. Once the signal level passes this level, the compressor will begin to apply the amount of compression set (determined by the ratio). If the signal level is not reached, no compression takes place.

Attack

Attack determines the time to reach the compression values. A fast attack time is great if you have a sudden spike in volume but a slower attack time will allow the initial transient to pass unaffected, which is vital for instruments such as drums.

Release

The release refers to how long it takes for the compressor to revert to normal, or to an uncompressed state. Faster releases can create a pumping effect whilst slow release times are much smoother.

Knee

This changes how the gain reduction behaves around the threshold level, but not all compressors have this. With soft knees, the signal is more loosely affected as it approaches the threshold but still tightens up again eventually.

Makeup Gain

This lets you add more gain to your compressed signal, it’s really just a simple volume control and will probably be labelled “Makeup” or “Output”. Once you have reduced the volume with compression, simply use the makeup gain to bring the signal back up to the same level as the dry signal and it will now sound louder.

Keep in mind that louder signals tend to sound better – this is one of the main advantages of compression – but make sure the makeup isn’t too hot just because it sounds good. Otherwise you will care less about how the dynamic range is being affected.

Next Steps

The more you use compression the more your ears will become accustomed to what it is and more importantly whether you should even be using it in the first place.

Of course one size doesn’t fit all and the way you compress an acoustic guitar will vastly differ to how you compress a snare drum.

Like a lot of things in audio production there is no right or wrong and so experimentation is a great way of finding your feet. This lets you hear what compressors you like and what sounds you can create with them.

Once you get to grips with compression you can try more advanced techniques such as sidechain or parallel compression. You’ll quickly find compression is a great tool to sculpting your mixes and adding depth and color.

If you need inspiration, check out some of our favorite tips from legendary producers!