What Is Dynamic Range Compression? (Audio Compression Explained)

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  • Learn how dynamic range compression affects audio
  • Understand how it is used in mixing
  • Get to grips with compression settings

Don’t get it twisted: dynamic range compression is just another way of saying ‘compression’.

If you’re new to audio production you may be wondering what compression is. If you’re researching mixing techniques then you can bet compression will be one of the first things you’ll read.

If you listen to any modern album you can guarantee compression will be used across the mix on different instruments, vocals and often the ‘master channel’ itself.

Compression can make or break a mix.

There are different ways in which to use compression to enhance your tracks but it’s also possible to over compress which can have a negative effect on your mix and create some nasty effects that can be unpleasant and distracting to listen to.

It can take a while to fully understand compression and its place in audio production, but luckily Producer Hive are here to guide you through the basics of compression.

Dynamic Range Compression Explained

In very brief terms – compression reduces the dynamic range of an instrument or track. Think of someone playing a song on an acoustic guitar, in this case, a quietly picked verse going into a loudly strummed chorus.

Dynamic range compression can be placed onto this track in order to tame the loudness of the chorus, while either not affecting the verse at all, or very little. You’re making the louder part quieter – i.e. compressing the range of dynamics in the track.

Compression could be thought of as a process that automatically turns down instruments or tracks automatically, based on parameters that you, as the engineer, decide.

Of course, in reality, it is much more complex than this.

The reasons you may want to compress can vary from track to track as can the compression settings and ever compression type that you choose.

As we’ve mentioned, being too aggressive can result in an over-compressed sound resulting in a lack of dynamics, however there are occasions where slamming your compressor can have equally impressive results.

Why Compress?

Compression can be used in a wide variety of ways to enhance your mixes and can almost become an instrument in itself.

One of the most common uses is to simply use compression to create an even mix in terms of volume. If you’re recording a vocal track and your singer moves from a quiet passage to a much louder passage, you can utilize compression to reduce the range of the second passage’s volume without manually having to automate the recording yourself.

This avoids an unnatural sound that will stand out to the listener due to the huge change in dynamics.

When we talk about reducing the volume through a compressor it is often referred to as ‘gain reduction’.

Imagine you’re having a conversation with a friend who is sitting next to you. At ‘normal’ talking volume you would be comfortable but if they started shouting right next to you it would be unpleasant. Imagine when they start to shout their volume is automatically turned down – you can still hear them shouting, but at an acceptable level, which eliminates any discomfort. A bit of a crude example, but an easy way to understand how compression works!

Compression can also be used to create a punchier sound on certain instruments like drums. By compressing a snare you can transform a mediocre sounding drum into a much more aggressive sound which can actually create what appears to be a louder sound – great for rock and metal style drums.

You can even use compression as a way of adding an extra layer to your mix, by creating a copy of a track through an auxiliary channel and heavily compressing the copy and blending to taste with the original. See our article on Pre vs Post Fader Sends to learn how to effectively do this. 

Compression Settings And What They Mean

Compressors come in either software or hardware form (i.e. a plugin accessed via your daw or a physical unit that you’d often see in studios).

Most compressors share the same parameters, although each one will have different sonic characteristics. If you’re new to compression it’s worth tweaking your controls to the extreme to see how they affect the sound.

While your DAW will likely come with its own compressors, feel free to explore our guide on some of our favorite FREE software VSTs.

The Audio Compressor - What It Is And Why It Is Used
Source: https://www.practical-music-production.com/

Threshold

The threshold control on a compressor relates to when the compressor kicks in and starts reducing the volume of your track. This relates to the volume in dB (decibels) of the track. 

If you’re unsure on where to start, simply lower the threshold until you start to hear the compressor kick in. If you’re unsure what to listen out for you will normally see a ‘gain reduction’ meter (which relates to the amount the track is being reduced by) which will indicate when the compressor is having an effect.

Ratio

The ratio on a compressor is simply the amount of gain reduction. You’ll usually see the ratio displayed as 1:1, 2:1, 4:1 etc.

These numbers refer to how much the compressor will reduce the gain by after the signal passes the threshold. 

1:1 means the compressor will reduce the signal to 1dB for every 1dB it goes over the threshold (so in actuality no compression is applied).

20:1 however would be regarded as a heavy compression setting where for every 20dB over the threshold the signal goes, it will be reduced to 1dB past the threshold. 

The ratio is incremental, so, for example, a 2:1 ratio would mean at 4dB the audio would reduce to 2dB, whereas at 10dB it would reduce to 5dB and so on.

Attack

The attack function relates to how quickly the compressor will kick in.

Think about what it is you are trying to compress when setting the attack time. A vocal, for example, will often want a fast attack time, allowing the compressor to ‘grab’ the vocal quickly and creating a smooth effect.

On a drum however, a slower attack is generally better allowing the transient (or the initial hit – short, sharp and aggressive) to cut through before the compressor starts. Try a fast attack time on your drums first to hear how the compressor ‘squashes’ the initial hit. Increase the attack time and you’ll hear the percussive sound start to come through.

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Release

The release time relates to how quickly the compressor returns to the point where it isn’t compressing the sound anymore, or its original volume.

A longer release time allows for more sustain in your track whereas a quick release can create a more percussive or pumping quality to the compression. 

Knee

Although not present on all compressors, the knee function relates to how smooth or how aggressively the compressor kicks in. A hard knee means the compressor is much quicker to start affecting the sound whereas a soft knee does the opposite.

Output Gain

The output gain decides what volume the signal leaves the compressor at. Whilst there isn’t a ‘correct’ way to set this, typically you want to ensure the signal leaves the compressor at the same volume as it enters the compressor.

You’ll often find a bypass button that will enable you to disengage the compressor and compare the two signals, allowing you to ensure the balance is correct.

Remember there are no right or wrong ways to compress. Try experimenting with settings and see what results you get.

Pro Tip: Volume match the compressed signal with the original, so your ears can accurately gauge the result of the compressor. A louder signal is often easy to misinterpret as sounding better, when in fact this might not be the case.

Getting Creative

The great thing about dynamic range compression is it really allows you to be really creative in your mixes, from subtle uses through to crazy sounds!

Once you have the basics of compression down, you can start to think about the type of compressor you want to use for each application. Some will offer a smoother quality, whilst some are punchier and add a pleasant distortion to your sounds.

You can even use compression to cause one instrument to ‘duck’ out the way of another (commonly used to momentarily lower a bass guitar to allow the kick drum more room in the mix). This technique is called sidechain compression (check out our sidechain compression tips and tricks guide).

Also, check out our article on the various types of compression to really lock in your knowledge about how compressors work.

More Compression Tips

It really is worth spending some time researching compression, but more so listening it to it yourself on your mixes, tweaking parameters and getting an idea of how it can shape your tracks.

As we’ve mentioned, over compressing can be a problem as it can eliminate the dynamics in your track altogether. Listen out for sibilance on your vocals (‘sss’ and ‘ttt’ sounds which can be exaggerated by over-compression) and a ‘washy’ sound on your instruments.

Another tip is to compress in stages

Instead of using ONE compressor to do all the heavy lifting, try using several different compressors one after another, all adding a small amount of gain reduction whilst adding their own coloration. This can help you achieve a smoother sound with lots of character, but most of all, you’ll have more control.

Experiment with your processing chain’s order

Experiment with EQ BEFORE compression, as well as EQ AFTER compression. Some schools of thoughts will try to convince you that one is better than the other, but our philosophy is that it depends.

Experiment with different types of compressors

Your DAW will often come with more than one compressor plugin, try comparing them all as you’ll get to know the qualities of each one and you’ll soon be on your way to being a compression master!

Also, check out our article on the various types of compression to really lock in your knowledge about how compressors work.