Beginner's Guide to Compression – Starting Quickly with Compressors and Dynamics
In this follow-along tutorial, we’ll help you to understand compression and compressor plugins, using your own tools and files
If you’re relatively new to music production, sooner or later you’ll have to learn about compression – or to give it its proper, full name, “Audio dynamic range compression”.
In this guide, we’ve designed a tutorial so you can use your own DAW and sounds to follow along and understand what’s happening when compressing your material. We’ll give you enough knowledge to work a compressor, understand what it’s doing, the change its key controls have on your signal, and how to use it in context.
For when you’re ready to move forward, we strongly recommend looking up the Top 8 Compressor Plugins on Plugin Boutique, and beefing up your mixing skills with 8 Simple Mixing Tips for Professional Results.
What is compression?
Compression is when you take a signal and “squeeze it” – that is to say, you make the loudest parts quieter, and/or make the quietest parts louder. In almost all cases, when we mention compression in general, we’re talking about making loud parts quieter.
Look at the waveform below (top), and the waveform below that (below bottom). The first was the original signal, and the lower one is a compressed version of that.
Comparing against the blue line, which is for your reference only, you’ll see that the top-most peaks of the signal have been lowered in the second signal – we’ve done that by using a compressor.
With these peaks lowered, they’re closer to the rest of the signal, which we now say has a lower ‘dynamic range’. The difference between its loudest and quietest parts is smaller than it was previously.
Here’s the part you need to wrap your head around: because the signal has shorter peaks and is generally quieter, we are now able to turn it up more.
Again, comparing the blue boxes, you’ll see that the dynamic range between various peaks in the audio file is greatly reduced – achieved by using strong compression and makeup gain.
How does audio compression sound?
It’s time for you to experience it for yourself.
Take three audio examples…
- A drum loop
- A vocal sample
- A synth arpeggio
You can source these from your DAW’s samples and synths, or get a Free Trial of Loopcloud to select from a huge number of sounds at your very fingertips.
Open any compressor plugin over any one of these sounds. Choose a preset from its presets menu.
Next, find the compressor’s Threshold control, and bring it down to trigger compression more harshly over the sound you’re listening to.
*In the event that your compressor doesn’t have a Threshold control, you may find an Input Gain control or Peak Reduction control on certain old-school-style models.
Bypass the compressor to hear the original sound, then toggle back again to hear the effect of compression. Try the same on different sounds, and using different presets (you may need to set the Threshold again).
But this is audio compression in its extreme form, and out of context. Now that you’ve heard the more lively side of dynamic range compression, it’s time to go back to the basics, and learn about what each parameter is doing in order to use it more properly, in context.
The basics of audio compression
Time to get into the nitty gritty of audio compression settings. Open a new compressor over your synth arpeggio sound (or similar). Here, we’re just using Ableton’s stock Compressor device – its workflow will apply just like any other similar device’s will.
The first thing to understand, in principle, is that the compressor will ‘activate’ (IE turn down the audio signal) when the audio signal gets louder than the Threshold you set. The amount of gain reduction that occurs is related to both the Threshold setting and the Ratio setting.
Compressor Threshold control
Start with the Threshold control. This should actually be lowered, not raised in order to cause more compression.
The Threshold sets the audio level (in dB), that when the signal exceeds it, gain reduction will be triggered by the compressor. The more the signal exceeds the Threshold you’ve set, the more the gain will be reduced.
In the image below, you can see the placement of the Threshold (blue line), the audio signal’s level over time (grey waveform), and the gain reduction (yellow line) triggering as the Threshold level is crossed.
Compressor Ratio control
Once the signal has breached the Threshold, triggering compression, the compressor has to work out how much compression to apply. This is done using both the Threshold, to determine the amount of deciBels the Threshold has been crossed by, and the Ratio, which determined how much gain reduction to apply.
Let’s say the Threshold has been breached by 4dB. At a Ratio setting of 4:1, the compressor will start reducing the signal’s gain by 3dB and only cross the Threshold by 1dB (a quarter). At a Ratio setting of 2:1, the compressor will reduce the signal’s gain by 2dB, ending up only crossing the Threshold by 2dB (half).
At even stronger compression ratios, for example 16:1, the 4dB signal will be reduced by 3.75dB, allowing only 0.25dB of level over the Threshold. For the same Ratio, a signal going 16dB over the threshold would be reduced by 15dB.
Timing a compressor’s action (attack and release)
The Threshold and Ratio controls may determine the depth and strength of a compressor’s gain reduction, but it’s the Attack and Release controls that can really have an effect over how your compressor is used, and the characteristics of its action.
A compressor’s Attack control controls how quickly it reacts to a breach in its Threshold. Does it need to hit immediately, to reduce the peak that triggered compression? Or is it intended to kick in more slowly, bringing down the level over the rest of the sound?
A quicker Attack will be more immediate and actually has a more heavy-handed response.
Next comes the Release control. If the Attack determines how quickly compression starts when the signal crosses the Threshold, then Release determines how quickly the compression backs off and returns to normal once the signal has gone back down over the Threshold.
A longer Release will mean that the gain reduction slowly goes back to normal, often being applied even after the signal has gone back down beneath the Threshold again. A shorter release will help the compressor ‘trace’ or ‘hug’ the signal peaks more closely.
Compressor Threshold, Ratio, Attack and Release Cheat Sheet
Low Threshold, High Ratio
This will cause heavy compression, which may be good as a creative effect or for parallel compression techniques.
High Threshold, Low Ratio
This will cause very light compression, which might be useful for mastering, or just causing small differences in character and response.
Quick Attack, Quick Release
This setup is designed to catch peaks (transients) quickly, making the result quite transparent. Set your Threshold to identify the highest peaks only, or just any material to trigger. Set the Ratio to define the strength of reduction.
Quick Attack, Slow Release
This introduces character into the compressor’s response, making it effective to start and lazy to stop again. It will react quickly to drum hits and quick impulses, and this effect will be felt for a while after each hit fades away.
Medium Attack
Set the attack time to kick in the compressor just after the transient of a sound, and you’ll end up leaving that transient untouched, and compressing the part of the sound just after it instead.
