What is a Compressor in Music Production? & How to Use it

Audio compressors are one of the most important tools in music production. This article will help you understand what audio compression is and how to use it when mixing and mastering your music. 

An audio compressor is a tool that automatically reduces the dynamics of sound waves by lowering the volume of louder sounds or amplifying softer sounds. It's also used to control or limit the dynamic range of audio signals, like an electric guitar, for example - this can give your music more consistency in terms of volume. 

When using compressors in your own production, there are three main controls you'll need to know about: Threshold, Ratio, Attack and Release Time.

These four main settings will determine how much audio compression you'll get. Compressors can be used for both subtle and extreme effects on audio, so don't be afraid to experiment! Below we'll cover everything you need to know about compression in music production in more detail - keep reading to learn more about audio compressors.

What is a compressor?

A compressor's job is to automatically reduce the dynamic range of an audio signal. This means that when the input signal goes over a certain level (threshold), it will be compressed by lowering the volume of sound waves above that threshold, which makes your music more pleasant to listen to and more homogenous.

If you are not familiar with compressors, here are some basics: a compressor is a device that automatically controls maximum volume levels to maintain an average loudness.

This prevents the different sound layers from competing against each other in the mix, and helps them flow together more naturally.

Here is an example of a sound without audio compression:

Now, here is the same sound with audio compression applied:

You'll notice that the version without audio compression sounded much flatter. The drums were not pumped as clearly throughout the synth sounds. Whereas, the version with audio compression decreased the synth's volume levels each time the  drum kicked in, helping the beat stand out and the synth flow around it.

How to use an audio compressor?

So, how do you use a compressor? Well first of all, you need to know the three main controls it has. These controls are Threshold, Ratio and Release Time.

- Threshold: The threshold is the point at which your compressor will start making any changes to your audio signal. To get a more subtle effect on your sound, set the threshold lower so that it's only affecting soft sounds. For a more extreme effect, set it higher so that it's affecting louder sounds.

- Ratio: This setting determines how much compression you'll get when an audio signal passes through - this can be both subtle and extreme depending on how high or low you set it. A higher ratio means that more of your audio will be compressed, a lower ratio means that less of your audio signal will be compressed.

- Attack time: The attack time determines how quickly the compressor kicks in. A fast attack time will make the compressor engage much more quickly than with a slower attack time.

- Release Time: The release time is the time taken for your compressor to return from compressing an audio signal. You can control this by using either a fast or slow release time. Fast release times typically give shorter but more intense dynamics, whereas slow release times give longer but less intense dynamics.

Threshold control 

The threshold control sets the level of sound that the compressor starts to work on.

For instance, if you set the compressor's threshold to -20dB, the compressor tool will not affect any sounds that are quieter than -20dB.

For sounds that are over 20dB, the compressor will kick in and reduce their volume levels.

When you increase the threshold by setting it to lower dBs, it makes the compressor start working on more and more sounds in your audio. This can produce a more dramatic effect, but setting the threshold to volumes closer to 0dB will result in more subtle compression.

Ratio control 

The ratio control determines how much compression will be applied to your audio signal.

For example, if you set the ratio at 2:1, then for every two units of volume beyond the threshold, only one unit will make it through. If you set it at 10:1, then for every ten units of volume beyond the threshold, only one unit will make it through.

The graph below shows how the ratio affects the sound's output level (dB).

Ratios are typically used to control volume and determine how much of the sound should be compressed. If the ratio is too low, the sound will be compressed 100% of the time, which can result in an unnatural sound.

Ratio can be used to easily reduce dynamic range, but can also be used to enhance creative sound effects, such as increasing sustain on a guitar. 

If you are trying to compress vocals in order to create more consistency in volume levels throughout your song, then you'll want to use a lower ratio like 3:1 or 4:1.

This way the compressor will bring down louder parts of the singers voice and amplify softer parts of their voice without making them too quiet. This is a common technique used in disco music to get that 'disco sound'.

Attack Time 

Attack time determines how quickly the compressor reacts to a signal. This is measured in milliseconds, measuring compression levels across a very small scale of time.

The quicker the attack, the more of the initial attack will be preserved and the faster the compressor will kick in.

For instance, if your attack time is set to 15ms, the compressor will kick in following a 15ms delay whenever it detects sounds above your set threshold level.

How you use attack will depend on the kind of instrument you are using your compressor on. Fast attack times are often useful for drums, as this can "duck" the volume of the drum when it's playing so it doesn't drown out other sounds.

However, for guitars and vocals, fast attack times can lead to an unnatural sound, which is why we recommend using a slower attack time - around 100 milliseconds or more - when compressing these types of instruments.

A slower attack time, such as 120ms will allow the start of the note (the transient) play without compression, while the rest of the note (the sustain) will be compressed.

Attack can be a really useful compression tool for creating either a punchy or more flowful rhythm, depending on what kind of style you want to create.

Here's an example of a sound compressed with fast attack:

Here is the same example sound compressed with a slower attack:

Release Time 

The release time is the amount of time it'll take for the signal to recover before the compressor can compress it again.

In other words, the release time is how long it takes your compressor to disengage with the input sound - this is the direct opposite of attack time.

The release will determine when the audio will return back to its original uncompressed volume levels.

Too much release time can result in an overly compressed sound, and equally if your release time is too quick, your sound levels might not be compressed enough.

As with attack time, there is no exact science when applying release time. The best way to determine how much attack and release time you'll need is to assess the audio by ear until it sounds natural.

A slow release time (1000ms) will result in a lot of compression and a fast release time (5ms) will result in much less.

Conclusion

Now that you know what a compressor is and how to use it, you are ready to put it to good use.

A compressor is a great tool for balancing the levels of your mix, or for taming an overly dynamic bass guitar or drum track.

You can also use a compressor to add punchiness to your drums or give a vocal track some thickness.

The true power of a compressor is in the control it gives you over the dynamics of your sound, so take some time to play around with the controls and find the perfect settings for your sound.