3 Commonly Used Types of Dynamic Compression

Once again you may find yourself sitting in front of your speakers, listening to your mix, and wondering: “Why are certain instruments getting lost in the mix while other are cutting through almost too harshly?” The problem you are facing probably has more or less to do with the overall dynamic range of your mix. Dynamic range refers to the ratio of the overall loudness of the various instruments. If you have a kick drum that is so loud it’s almost distorting, paired with a really soft female vocal, chances are you are going to be sacrificing the quality of one of them in your mix if the proper tools aren’t used.

The “magical tools” I am speaking of are the tools and techniques of dynamic compression. Compressors are some of the most important plugins an engineer can have in their DAW, because they allow you control and manipulate the dynamics (loudness) of your sound waves. The 3 most commonly used types, or techniques, of compression are:

  • downward compression
  • parallel (upward) compression
  • side chain compression.

All three are commonly used throughout everyday mixing, and each has their own purpose and place for use. I’m going to go ahead and briefly explain each type, as well as practical situations or uses for each.

Before we start remember! Nothing said in this article is meant to be 100% “gospel.” There are many times when trusting your ear can be the most valuable tool. The plugins are there for guidance, but ultimately you must makes decisions off of what sound good. Let’s get started!

Downward Compression

The most familiar and commonly used type of compression among most engineers and producers is downward compression. This refers to evening out the average loudness of a sound wave by decreasing the signal level of all sound that is above a certain threshold, while leaving anything below the threshold unaffected.
In simpler terms, it brings the loud noises down closer in relation to the quiet noises, all while leaving the quiet noises unaffected.

This is a great technique used almost every time on instruments like drum kits, electric guitars, and vocals. To give a clear example, let’s say you have an electric guitar track that goes from a soft bridge section into a louder, in your face, guitar solo. You can use some downward compression here in order to bring that dynamic solo section down to closer relation to the bridge. If not, later when drums and other instruments are added, the guitar parts aren’t going to sound balanced with each other. You’ll either have a really quiet bridge that is masked by the drums and louder instruments, or you’ll have a guitar solo that is way too loud and basically ruins your mix.

By being able to bring louder parts of a sound wave down closer in relation to the quitter parts, give you a lot more total control of the loudness of your overall mix. This is my preferred technique for compression, because I find it allows for me to have the most headroom available at the end of mixing.

Parallel (Upward) Compression

Parallel compression, also known as upward compression, is commonly referred to as New York Style Compression, and is the exact opposite of downward style compressing. If you apply this concept you can understand that with parallel compression the quieter signals below the set threshold will be brought up in closer relation to the louder, unaffected signals above the threshold.

Some compressor plugins allow you to achieve this by bringing the ratio down to 1:1 or lower. The compressor will then begin to act almost as an expander, allowing you to bring up the quieter levels. The most common way of performing this technique though is to blend an uncompressed, clean signal with a copy of a very heavily compressed signal. (hence the name parallel compression.) This is a great technique for adding life and character to what would other wise be more stale, plain instruments.

Parallel compression is a great technique to use when mixing drums! (Especially works well on overheads or sub mixes.) Remember the whole idea is to simultaneously mix a dry signal with a very heavily compressed signal to achieve more of a dynamic pop from the instrument. A great place to start with your compressed signal is with a very low threshold. You basically want your meter to always show some compression happening (really crush it). Keep your attack time as quick as possible to make sure the compressor is capturing all of the transients in your sound wave. Once you have your compressed signal, slowly add it into your dry signal, and look for a harmonious balance. Afterwards, go ahead and switch between muting and unmuting the compressed signal, and listen to how much of difference it will make!

Side Chain Compression

The last of the 3 compression techniques I’m going to talk about is side chaining, or side chain compression. This form of compression differs from the previous two by the fact that it doesn’t actually operate off of the signal you want to enhance, or make louder. Side chain compression is basically a way to make an instrument stand out in the mix by compressing the other ones around it. Many compressors allow you to side chain them to other instruments, so that compression only happens when the instrument is playing.

Have you ever had a kick drum that sounds fantastic on its own, but as soon as you add the bass guitar and other low-end instruments it gets lost in the mix? This common dilemma has been experienced by many, and is known as masking. I’m here to tell you that side chain compression is one of the all time best deterrents to masking and cluttered sounded instrumentation! Yes, your kick drum was sounding perfect, but now all it is, is lost in the mix and the bass is rumbling all over that rhythmic punch that you’re looking for. All you would need to do is side chain the signal of your kick drum to compressor located on the bass guitar track. Send the kick drum to a post fader aux bus, and put the compressor of your choosing on the bass tack. It’s important to make sure that the compressor plugin you are using supports side chaining (H-Compressor, C1 Compressor, RComp). Once you have the plugin on your bass track, you should be able to select the kick drum bus underneath the side chain functions. When properly done the compressor will activate and bring down the bass guitar whenever the signal from the kick drum triggers it. Side chaining is one of my all time favorite ways in creating more separation for my kick drum!

Compression – along with mixing in general – really starts to become more of an art than science when you begin diving deeper into processing and editing audio. The art of compression is one that takes time to understand and is can be quickly misused if not careful.

Compression isn’t meant to be used to crush every single sound wave and give no breathe to the mix. Its there for us to use delicately in order control parts of the mix that tend to jump out or get masked without intention. It’s there to help us achieve balance and separation through dynamics, which can help leave a lot of room for further EQing and other processing further in the mix. The best way to familiarize with these 3 common techniques is to put them into practice in the studio.

Take a mix you’ve been working on and experiment with compression. Listen for what your vocal track sounds like with downward compression. What about parallel compression? Soon enough you’ll have such a grasp on the topic you’ll be able to implement your own self-found compression techniques and tips that’ll have your mixes sounding so dynamic people will be wondering what fancy plugins you used to achieve that crisp sound. There’s nothing fancy about compression – just practical.