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All Compressor Types Summarized

First things first: A compressor is a tool that tames peaks (reduces the dynamics) of an incoming signal to allow you to have an overall more balanced-out performance. There are many scenarios why and how you can use a compressor, however, the main purpose (in the 50s) was to create a tool that helped the recording engineers to not ride the volume faders all the time during a performance, as music can be extremely dynamic.

 

As I have said before, during the past 70 years the recording industry came with many different types of compressors…and these are:

 

VCA – Voltage Controlled Amplifier

 

• The VCA compressors are the most versatile of all types of compressors

• Most used type of compression

• They are fast, smooth and are not very colorful, thus don’t change the sound characteristics too much

• Popular choice for bus compression and mastering

• Have all typical controls of dynamic processors: attack, release, threshold, ratio, and knee

• Most famous VCAs are the SSL & Neve channel strips compressors, the dbx 160A, and the API 2500

 

Technical information

 

The electrical circuit is split into two paths:

 

(1) Detector path: When a certain voltage is reached, the compressor turns down the signal, thus controls the compression effect

 

(2) Output path: Is what you hear in the end

 

Simulation of an SSL channel strip by brainworx
Simulation of an SSL channel strip by brainworx

Opto / Optical Compression

 

• Used for vocals, lead instruments, bass and rounding out a performance (think of a long-term event)

• Sound characteristics: Smooth, natural and musical sound

• Can handle more gain reduction, yet still sounding natural, as the attack and release times are slower overall

• Famous Optical Compressors: LA2A & Tube Tech CL1B

 

Technical information

 

• Compression depends on light (light-dependent resistors)

• The audio signal feeds a light element which operates through a light-sensitive resistor

• Resistor acts like a pipe: Gain says how much is going into the pipe and peak reduction says how much is going out of the pipe, or in other words, the more resistance a.k.a peak reduction, the more compression overall

• Optical compressors add color as there are many different types of light sources and resistors available

 

Simulation of an LA2A by Native Instruments & Softube
Simulation of an LA2A by Native Instruments & Softube

FET Compression

 

• Best use for hard peak limiting tasks (super-fast attack & release times)

• If you want something „in your face“ like vocals, you’ll better grab a FET compressor

• In general not a good fit on the master bus

• They add color to the source material

• Most famous: Urei 1176

 

Technical information

 

• The electrical circuit is based on transistors (transmitter + resistors) and operates with the electrical field in addition to voltage (not the same as VCA)

 

Simulation of an Urei 1176 by Native Instruments & Softube
Simulation of an Urei 1176 by Native Instruments & Softube

Vari-Mu (Variable-Mu by Manley or originally Delta-Mu)

 

• Adds glue and is used not for dynamic control in first place

• Gentle type of compression (mix bus)

• Sounds like a soft-knee effect

• Not suitable for an aggressive type of sound

• Adds color without even limiting the material (tubes)

• The sound quality is smooth, rich, thick & creamy

• Transients are treated in a musical way

• Speed response is the slowest compared to the other types of compressors

• Can handle more gain reduction before unwanted artifacts occur

• Most famous: Fairchild 660 & 670

 

Technical information

 

• Compressors are based on tubes

• While Opto-Compressors can use tubes for color, Vari-Mu compressors use tubes to tame dynamics

• The ratio increases as you push the unit harder, so this technique sounds musical and pleasing to our ears

 

Simulation of a Tube Compressor by Native Instruments & Softube
Simulation of a Tube Compressor by Native Instruments & Softube

BONUS

 

Diode-Bridge Compression

 

• Most colorful compression of all, as a diode itself adds colorful distortion

• The Neve 2264 500 series unit is one famous example of diode-bridge compression

 

PWM - Pulse Width Modulator

 

• A pulse width modulator circuit creates almost no artifacts, thus no color (the cleanest compressors of all)

• Extremely difficult to build, thus extremely rare

• Modern unit of a PWM compressor: Great River PWM 501

 

Well, I didn’t cover how you use a compressor, however, it’s another topic on another day. But for now, you know that a compressor is not always the same compressor with the same "processor".

 

Use this guide as a reference for your next projects and productions. Get familiar with those different types, as you are NOT confused anymore. :)

––

To your success,

Alexey

 

Creator of Make Better Music Now

www.makebettermusicnow.com


ABOUT ME


Hi, I’m Alexey aka JLX,

it’s nice to meet you!

 

I am a Germany based composer,

sound designer, mixing engineer and coach.

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