If you’re relatively new to the studio and are trying to figure out ways to elevate the quality of your recordings, it’s essential to learn a little about audio compression. The term may sound daunting, but the basics of this technology are not too difficult to learn. In fact, after reading this simple and brief guide, you should be able to start implementing compressors into your tracks right away.
What is an Audio Compressor?
In its simplest terms, a compressor is used to “smooth out” the dynamics of a track. It does this by reducing the difference between the softest and loudest parts of the track to make the overall volume more consistent and even throughout. When used skillfully, it results in a louder, more cohesive and more professional sounding track.
However, it can also be used in more advanced ways to bring out certain sonic characteristics, not only in the overall track but also with respect to singular instruments. For example, it can make your drums punchier or your bassline tighter. It can soften sharper elements, while making other elements more energetic. In fact, a compressor can be an essential tool for shaping your sound and giving it the personality you’re aiming for.
Do I Need a Compressor for My Studio?
Yes, you do generally need a compressor, but probably not a outboard/external compressor if you’re working in your home studio. Your DAW usually offers compressors, or they can be downloaded as plug-ins. Plug-in compressors have become so good at emulating the classic compressor hardware that it’s hard to tell the difference. So, since most of us are working in the digital domain, an external compressor tends to be unnecessary. For this reason, many of the compressors I’ve listed as examples below are digital plugins.
The compressor above is one of several models included in Apple’s Logic Pro.
Now, let’s take a look at the typical controls you’ll see on a compressor. To keep things simple, we won’t go into advanced compression techniques (like side-chain compression or multi-band compression). Rather, we’ll just cover the basics to help you get started.
Types of Compression Controls
Threshold
The threshold is the point at which the compressor starts working, reducing the volume of the audio signal. As long as the signal stays below the threshold, it won’t be affected by the compressor. But as soon as the signal reaches beyond the threshold, compression will start. So, if your threshold is set at -10 dB, the compressor won’t kick in until the signal extends above the -10dB level.
Knee
The knee refers to how smoothly or sharply the compressor starts reducing gain once the threshold has been crossed. So, if it’s a “soft knee”, the compression gradually eases in and if it’s a “hard knee”, the transition will be more abrupt. So, a hard knee setting would work well for fast peaking instruments, like drums, while the more gradual transition of a soft knee tends to work well for vocals and certain other melodic instruments.
Ratio
The ratio decides how much the compressor reduces the signal after it’s moved beyond the threshold. For instance, a 4:1 ratio means that for every 4 dB that the signal would have extended beyond the threshold, it will now only reach above that threshold by 1dB. So, then it basically becomes a “limiter”, as it limits the loudness of the signal.
Attack
The attack controls how quickly the compressor reacts to the signals exceeding the threshold. This result is often difficult to visualize unless you actually hear its effect in practice. So, let’s take a snare drum as an example. With a fast attack, the compressor is activated as soon as the snare hits. Consequently, there will be a mellowing of the snare impact. But if the attack is slower, the sharpness of the snare will remain intact, while the last part of the snare sound will be softened. Here, I should underscore that “attack” and “knee” are different. While the knee decides the “manner” in which the compressor will react, the attack decides the speed at which the compressor will react.
Release
The release decides when the compressor stops affecting the signal. Here it’s important to note that even if the input signals fall back below the threshold, the compressor doesn’t suddenly stop. It will continue to do its work based on the release time you have set.
Again, let’s think about how this theory translates into practice and how interacting with the release and attack settings will affect the sound. As mentioned above, if the attack is fast, the initial sharp impact of the snare will be softened. Now, if you pair this setting with a fast release, then the end of the snare sound will stay uncompressed. As a result, you’ll hear a tempered attack, and pronounced resolve. And just to really hit this idea home, if you’re looking for a more crisp/staccato effect, you’ll want to pair a slow attack with a slow release. Yes, these ideas can get confusing, but once you play around with it a bit, the controls will become instinctive.
Makeup Gain or Gain
Gain or makeup gain is just what it sounds like. It boosts the overall level of the signal to make up for volume that has been lost through compression. In other words, since compression quiets down the signal, you need to add gain to bring it back up to a suitable level in your mix. This process lets your tracks reach a level of loudness that might have been missing before compression.
Common Types of Compressors
VCA Compressors (Voltage-Controlled Amplifier)
VCA compressors, such as the Warm Audio BUS COMP, are one of the more commonly used types in studios. They’re reliable in that they’re quick and precise, offering a clean and punchy feel, while adding cohesion to the track. They’re also quite transparent and usually tend to avoid coloring the sound.
Optical Compressors
This compressor is great if you’re looking to smooth out your sound. It has a highly musical and fluid feel, yet it tends to even things out without changing the overall character of your track.
FET Compressors (Field Effect Transistor)
FET Compressors can deliver quick attack and release times. Like the Pulsar Audio 1178 FET Plug-In, these compressors are often fast and bright sounding, great for adding serious punch to percussion and drums without squashing their natural tone. Their ability to keep things sounding authentic also makes them great for acoustic instruments.
Tube Compressors
Tube compressors tend to have a slow attack time. They have a less obvious tightening effect than other types of compressors. As result, they usually offer cohesive or “glued-together” sounding tracks. And more famously, they add color, warmth and harmonic richness to the sound, giving it that vintage vibe. The Nomad Blue Tubes Compressor CP2S is a fun example.
PWM Compressors (Pulse Width Modulation)
I mention this one last because PWM compressors often get less attention than the types mentioned above but they can execute impressively fast attack and release times. Subsequently, they’re especially useful for less hard-hitting musical genres, and an especially handy option if you’re looking for a super transparent and natural sound.
Let’s Wrap Up
At the end of the day, it will take some playing around with various types of compressors and their controls to find the sound you’re looking for. And you’ll notice that different tracks will call for different compressors and settings. In general, though it’s very easy to learn the basics of compression, achieving more advanced or specific results will take some time and research. But I recommend diving in right away. You’ll be surprised what a simple compressor plug-in can do for your track in just a few minutes.
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