Using audio compression is an essential part of mixing popular music, so it is a vital skill to develop. There is so much you can do with an audio compressor, but as a beginner, it can be confusing where to start. Here I will outline some of the basic things that will help you to use audio compression better.
This is part four of our audio compression series. If you haven’t read the previous post on types of audio compression go ahead and do that so you can more out of this post.
Before we jump into how to use audio compression correctly in mixing, there are two terms you need to understand first. Audio compressors are dynamic range processors, so you need to know what dynamic range means.
When you hear the take about compression, you hear the word transient, which you also need to know.
What is dynamic range
Dynamic range in music production describes the difference between the loudest and the quietest levels of an audio signal.
Very dynamic audio makes it difficult to achieve a reliable balance between instrument when mixing.
Take a vocalist for example who sings very high on some note and low on others. When you set the fader level so that the low notes are audible against the other instruments, the loud ones will stick out like a sore thumb.
Setting the fader where the loud the notes balanced with the other instruments, the low levels will get overpowered.
This is where audio compression comes in. You use it to reduce the sound’s dynamic range so that you’re able to balance the mix better.
What is Transient
Transients are the initial impact that you hear at the start of a sound. They determine how loud you can tune the sound up before it starts clipping.
However, the perceived loudness level (how we hear sounds), is based on the average level.
The means you will have to raise the average level for the listener to perceive the sound as being louder.
Raising the average level will also raise the loud transients in the sound, which could cause clipping and distract the listener.
By reducing the transient volume, you will not only prevent clipping, but you will have more headroom to raise the Average level higher, resulting in an overall louder perceive loudness.
What does an audio compressor do
If you read the previous articles in this series, you should have some idea what a compressor does. You should also know the type of controls on a compressor and how they work.
If you haven’t, here is a quick run-through. Compression reduces the sound’s dynamic range. It attenuates the loudest parts of the sound so that they are more consistent with quieter parts.
The controls on a compressor that you use to achieve this are the threshold, ratio, attack and release.
The threshold set the signal level in dB where the compressor starts to operate. Singal that goes above the threshold level gets compressed and signal that falls below remain untouched.
The ratio determines how much the signal is compressed once it passes the threshold. Higher ratio means compression.
Attack and release determine the reaction speed of the compressor. The attack is the time it takes the compressor to start compressing once the signal goes over the threshold.
While the release is the time it takes the compressor to stop compressing once the signal falls below the threshold.
How to use audio compression
The first thing you should ask yourself once you decide to use a compressor is what are you trying to achieve. Are you adjusting the transients and dynamics range or adding character?
To change the dynamic range and transient start with a ratio setting of 3:1 or 4:1 when compressing individual tracks. Set a lower ratio if you are compressing an entire mix.
Lower the threshold until you are getting 6dB of gain reduction. You won’t have much noticeable difference with 6dB of gain reduction. But once you go beyond 6dB, the sound’s timbre may start to change.
You don’t want to compress the audio so much that it destroys all the sound’s dynamic, because this will result in a lifeless mix.
Now set the attack time, this will depend on the audio and what you are trying to achieve.
A slower attack time will preserve the snap of the transient. Start with an attack time of 100ms.
Faster attack time will smooth out the sharpness of the transient and make the sound feel a bit thicker. Start with an attack time of 15ms.
Set the release time some that the gain reduction meter needle moves rhythmically with the audio being compressed.
Start with a fast release time and increase it until the compressor reduction meter needle is moving in time with the audio signal.
By no means these settings will work for every audio and with every compressor, but this is a starting point.
And if you are using the compressor to add colour, the setting will be different.
Things to consider when using audio compression
Audio compression can be a complicated process when you are just learning how to use it.
But you get better at using the compressor once you understand its basic principles.
Here are a few things to consider when using the compressor that would help make using audio compression better.
- Use more than one compressor: Don’t be afraid to use multiple compressors on a signal track. Instead of a simple compressor with heavy compression, use two in a row with subtle compression. This way you are able to keep more of the natural character of the sound.
- Fast attack and release can cause distortion: Setting very fast attack and release times when compressing low-frequency sounds will cause it to distort. Low frequencies have long waves so, which means more time is needed for the sound to get beyond the threshold level before the compressor starts to operate.
- Every compressors aren’t this same: Compressors differ in terms of tone and how they affect the audio signal. Some compressors are faster than others, and some will sound brighter than others. FET and analogue emulators add colour and harmonic distortion to the sound. Read more on types of audio compression here.
- Percussive sound and fast attack: Percussive sounds such as a snare drum hit or a guitar pluck have loud transient. Some beginner engineer thinks the fast attack is the best setting to reduce the initial impact of these instruments. An attack time that is too fast will slam the initial transient so much you will lose the character of the sound. Remember, percussive sounds are made up of mostly the initial hit and little body.