The second post in our audio compression series, this post is all about the four common types of audio compressors. In the first post, we wrote about what a compressor is and how it works.
Young mix engineers often find it hard to wrap their heads around the audio compressor.
Many use it even without knowing much about the tool, believing it makes their mix better only to kill the mix.
The purpose of this series is to change that. In the post, we go over the four common types of audio compressors, how they work and affect the audio.
Four Common Types of Audio Compressors
VCA – V is for versatile… jokes, it’s not. VCA stands for voltage-controlled amplifier, which is the circuit type used in these compressors.
But versatile describes this type of compressor perfectly. Whether it is recording, mixing or mastering, VCA compressor gets the job done in every area of audio production.
Voltage-controlled amplifier compressor uses an integrated circuit (IC) chip-based transistors that respond to the voltage of incoming signals, which gives them the transparent characteristic that VCA compressors are known for.
Because of there clean sound, fast attack and the ability to glue a mix together, VCA compressors are most often used as a buss compressor.
Most modern compressors you come across will likely be a VCA compressor because the circuit design is cheaper to source.
They tend to have all the basic compressor parameters (threshold, ratio, attack and release), which gives more control to fine-tune the setting.
Very popular VCA compressors are the API compressor and the SSL channel strip.
FET or “Field Effect Transistor” is the beast of all compressor designs. It is aggressive and has a unique coloured tone that many professional mix engineers love.
It has the fastest attack and release reaction time of all four designs. More often than not, the slowest time on FET compressors are faster than the fastest time on Variable-Mu compressors (see below).
The transistor circuits of FET compressors add subtle harmonic distortion that gives the audio a rich character and colour.
If you want soft compression the FET won’t do the work.
Because of there aggressive nature and highly-coloured characteristics, FET compressors are almost never used on the master buss or for mastering situations.
They are great for when you wish to create big punchy mixes. Mostly used for parallel compression situations, on drum busses, on the kick, snare and loud guitars or on vocals to bring it up front in the mix.
The most popular FET compressor is the 1176, which have been emulated by almost every top plugin manufacture.
Optical or Opto compressor reacts slower to input signal than the compressors mentioned previously.
It produces a more “natural” sounding gain reduction. It has a softer attack and release time, which gives it a smoother sound texture.
This is a very popular choice of compressor because of its subtle, transparent, and musical sound quality.
Don’t think because I have said little about this type of compressor, it is less than the others.
In fact, optical compressors are one of the most used because of it musical effect.
Variable Mu Compressor
Variable-Mu compressors may be one of the oldest compressor designs., which offers a sound that is often hard to get with other compressors.
They use tubes and transformers to control the gain-reduction, making then very slow acting compressions.
Think of the Variable-Mu compressor as an “ultralong” soft knee compressor.
Just like a soft knee effect, the amount of compression gradually increases as most signal hits the compressor input.
The effect of this is a warm, smooth, and distinctive “vintage” colouration.
The variable-mu isn’t the ideal compressor for intense, aggressive gain reduction.
A very popular variable mu compressor is the Fairchild 670, which Wave emulate with their PugChild 670 plugin.
As a mix engineer, it’s worth knowing what the different types of compressors are, how they work and which application they work best in.
This way you know which compressor to try one any given instruments or with any given compression techniques.