As a producer, it’s essential to understand how each tool functions. Compression is one of the most commonly used audio processors, yet so few budding artists take the time to understand what a compressor actually does.
Luckily, we’ll dive into everything you need to know about compressors below. We’ll also share the differences between various types of compressors so that you can always pick the right plugin or hardware piece for the job.
What Is A Compressor?
Compressors have been around since the early days of radio in the 1930s. Today, we have many different types of audio compression, both digital and analog, that essentially accomplish the same task: Audio compressors are designed to reduce the dynamic range of an audio segment.
What that means in lamen’s terms is that compressors bring up the quietest sounds while lowering the loudest sounds in a piece of audio, effectively creating a more consistent volume level throughout a track. It’s one of the few processing methods that’s used throughout the recording, production, mixing, and mastering process.
Some compressors strictly address the dynamic range of audio, while others can add a bit of color and shape the transients of a song. Every compressor has its own distinct character, which is why producers may prefer to use one compression type over another depending on the circumstances.
What Are The Different Parts of the Compressor?
Here are the standard parts of audio compressors. Not all compressors will have all of these parts, but it’s worth understanding each element as a producer.
Attack
The attack controls how fast a compressor processes an audio signal.
Release
Release is the opposite of the “attack” control and dictates how quickly the compressor releases or stops affecting the audio signal.
Threshold
The threshold is the point at which the compressor springs into action, measured in decibels (dB).
Ratio
Ratio determines how much compression is being applied to an audio signal. The higher the ratio, the more compressed a signal will be.
Knee
The knee can be defined as the “slope” of compression. A hard knee creates a more obvious compressed effect, while a soft knee is more subtle.
Gain Reduction Meter
This indicates how many decibels of the loudest part of the audio is being compressed.
Makeup Gain
Some compressors have a makeup gain toggle designed to add back in amplitude after it’s been lost due to gain reduction.
Wet/Dry Knob
As it does on any plugin, the wet/dry knob determines how much of the audio signal overall is processed by the compressor.
Audio Compressor Types Explained: Analog and Digital Compression
Now that you understand the principle role of compression let’s dive into some more specifics. Here’s what you need to know about each type of compression and how they function within a project.
Hardware Compressors
As the name suggests, hardware compression was conducted on consoles outside of an engineer’s DAW, though many digital compressors are designed to emulate hardware sensibilities. Hardware or analog compressors tend to have more of a “coloring” effect than most digital compression devices since physical units produce some level of operational noise.
VCA Compressor
VCA stands for “voltage-controlled amplifier” which is what powers this type of compressor. These compressors are known for being incredibly responsive, leading many to use this type of compressor on drums or any piece of audio that could benefit from transient shaping.
Optical Compressors
Optical compressors divide a signal and use a light source to autodetect how much compression a sound needs. These compressors typically have a fixed ratio, and although somewhat slow, produce pleasant, smooth sounds making them a popular choice for vocals.
Tube Compressors / Variable Mu Compressors
Tube or Variable Mu compressors are some of the oldest compression types you can find. These compressors use analog tubes to control gain reduction, creating a warm, smooth sound. They aren’t the fastest compressors on the block, but they are great for adding a bit more of that warm, nostalgic sound to your mix.
FET Compressor
Field Effect Transistor compression was developed after tube compression to produce the variable-mu’s coveted warm sound with a faster reaction time. Since it emulates tube circuitry, this compressor certainly colors sound creating a punchy, pleasant tone.
PMW Compressors
PMW compressors or Pulse Width Modulation compressors utilize high-frequency signals to control the amplitude of a sound. While these rare compressors are fairly new, they are said to produce fast-acting compression with low levels of digital distortion.
Digital Compressors
Digital compression only exists within a DAW and can possess unlimited headroom, unlike a hardware piece. Some digital compressors are designed to emulate the effect of hardware compressors.
Glue Compressor
Glue compressors are digital compression plugins designed to emulate hardware equipment from the 80s, and “glues” tracks together. These compressors are designed to be used on audio busses or groups to create a more cohesive sound across individual tracks.
Multiband Compressor
If a compressor and EQ had a baby, a multiband compressor would be born. Essentially, this device allows compression to be applied across a set frequency range based on the adjustment of EQ bands.
Low-Level Compressor
Low-level compressors bring up the volume of the quietest sounds in a piece of audio based on the compressor threshold but do not attenuate the loudest parts of a signal.
Compression Methods
These aren’t necessarily specific to any compressor, but types of compression for processing different pieces of audio:
Limiting
A limiter is essentially an ultra-charged compressor, with high ratios of compression. This compressor is used sparingly and typically reserved for the mastering process.
Sidechain Compression
Sidechain compression isn’t a compressor type itself, rather it’s a method. In this process, a compressor attenuates a sound based on the input from another sound. For instance, an engineer might sidechain the bass in response to the kick drum. So, every time the kick drum plays, the bass ducks in volume resulting in a more impactful kick and cleaner mix.
Parallel Compression
Parallel compression, sometimes called New York compression, is when only part of the audio signal is compressed, blending the source signal with the compressed one. Any compressor that has a dry/wet knob can easily produce this effect, though you can also create parallel compression by sending a portion of your audio signal to a send track with compression. This compression method usually gives engineers more control over the blend of a song and can help preserve some of the original energy of a track.
Hopefully, this guide makes it easier for you to understand how compression works and which compressor type makes the most sense for your project. Be sure to experiment with different compression types to find what works best for you.