Compressor/Limiters: The Ultimate Guide

Introduction

Compressor/limiters are an essential tool in the recording and mixing process. They help control the dynamics of a sound source, making it sound more polished and professional. In this article, we’ll cover everything you need to know about compressor/limiters, including their primary controls, types, famous models, and setup.

Primary Controls

Threshold

The threshold control determines the level at which compression starts to occur. Signals below the threshold remain unaffected, while signals above the threshold are compressed.

Attack Time

The attack time control determines how quickly the compressor reacts to signals above the threshold. A fast attack time is suitable for controlling transients, while a slower attack time can help maintain the natural character of the sound.

Release Time

The release time control determines how quickly the compressor stops compressing after a signal falls below the threshold. A fast release time is suitable for percussive sounds, while a slower release time can help maintain the natural decay of the sound.

Compression Ratio

The compression ratio control determines the amount of compression applied to the signal above the threshold. A higher ratio results in more compression.

The compression ratio is like a volume knob that turns down the loud parts of a sound. The higher the ratio, the more the loud parts are turned down. A ratio of 2:1 means that for every 2 loud parts, the compressor turns down 1 of them. A ratio of 4:1 means that for every 4 loud parts, the compressor turns down 1 of them. A ratio of 8:1 means that for every 8 loud parts, the compressor turns down 1 of them. When the ratio is set to infinity, it means that the compressor won’t let anything go over a certain level, so it’s like a volume limit. Imagine you have a music player and set a maximum volume level so it doesn’t get too loud and hurt your ears. That’s what a limiter does. It sets a maximum level for the sound so it doesn’t get too loud and cause damage to your ears or the equipment.

Typical ratios you’ll find on most compressors include:

2:1 – For every 2 dB that the signal goes over the threshold, the output will be compressed by 1 dB. This is a mild compression ratio that is suitable for subtle dynamic control.
4:1 – For every 4 dB that the signal goes over the threshold, the output will be compressed by 1 dB. This is a moderate compression ratio that is suitable for general-purpose dynamic control.
8:1 – For every 8 dB that the signal goes over the threshold, the output will be compressed by 1 dB. This is a high compression ratio that is suitable for heavy dynamic control.
Infinity:1 – The output will be fixed at the threshold level when the compression ratio is set to infinity. This is known as limiting and is used to prevent signals from exceeding a certain level.

Side Chain

The side chain input allows an external signal to be used to trigger the compressor. This is useful for de-essing, ducking, or frequency-specific compression.

Possible Uses

De-essing: using a frequency-specific signal to reduce sibilance in a vocal recording
Ducking: reducing the level of music when a voice-over is present
Frequency-specific compression: compressing only a specific frequency range of a signal

One interesting use of side chain is to create unique effects. For example, you can use a kick drum to trigger a compressor on a bass guitar track, resulting in a pumping effect that is often heard in dance music. Another example is to use a vocal track to trigger a delay effect on a guitar track, creating a rhythmic pattern that complements the vocal melody. The possibilities are endless, and experimenting with side chain can lead to some truly creative results.

Bypass

The bypass control allows the compressor to be bypassed, allowing the original signal to pass through unaffected.

Types of Compressors

Optical

Optical compressors use a light-dependent resistor (LDR) to control the amount of gain reduction. They are known for their smooth and musical sound.

Example: Teletronix LA-2A

The Teletronix LA-2A is a legendary optical compressor that has been used on countless recordings. Its smooth and transparent sound makes it a favorite among engineers and producers.

FET

FET (field-effect transistor) compressors use a FET to control the amount of gain reduction. They are known for their fast response and aggressive sound.

Example: Universal Audio 1176

The Universal Audio 1176 is a classic FET compressor that has been used on countless recordings. Its fast attack time and aggressive sound make it a favorite among rock and pop engineers.

VCA

VCA (voltage-controlled amplifier) compressors use a VCA to control the amount of gain reduction. They are known for their transparent sound and fast response.

Example: DBX 160

The DBX 160 is a classic VCA compressor that has been used on countless recordings. Its transparent sound and fast response make it a favorite among engineers and producers.

Vari-Gain

Vari-Gain compressors use a variable gain amplifier to control the amount of gain reduction. They are known for their warm and musical sound.

Examples: Fairchild 670 or Manley Vari-Mu

The Fairchild 670 and Manley Vari-Mu are classic Vari-Gain compressors that have been used on countless recordings. Their warm and musical sound makes them a favorite among engineers and producers.

Limiting

Limiting is a type of compression that is used to prevent signals from exceeding a certain level. Limiters typically have a very high compression ratio, and are used to prevent clipping and distortion.

Famous Compressor/Limiters

Teletronix LA-2A

The Teletronix LA-2A is a legendary optical compressor that has been used on countless recordings. Its smooth and transparent sound makes it a favorite among engineers and producers.

Universal Audio LA-3A

The Universal Audio LA-3A is a solid-state version of the LA-2A that has been used on countless recordings. Its smooth and transparent sound makes it a favorite among engineers and producers.

UREI LA-4

The UREI LA-4 is a solid-state compressor that has been used on countless recordings. Its fast attack time and transparent sound make it a favorite among engineers and producers.

UREI 1176

The UREI 1176 is a classic FET compressor that has been used on countless recordings. Its fast attack time and aggressive sound make it a favorite among rock and pop engineers.

What happens when you push-in all four ratio buttons simultaneously?

When all four ratio buttons are pushed in simultaneously on a UREI 1176, it produces an infinite compression ratio, resulting in a heavily compressed sound.

Plugin Versions of these Famous Compressor/Limiters

These are some of the popular plugin versions of these famous compressor/limiters available in the market todaye:

UAD LA-2A – This plugin is a faithful emulation of the classic Teletronix LA-2A and is available for $299 on the Universal Audio website.
Waves CLA-76 – This plugin is modeled after the Universal Audio 1176 and is available for $299 on the Waves website.
Universal Audio 1176 plugin – This plugin is a faithful emulation of the classic 1176 and is available for $299 on the Universal Audio website.
Softube Tube-Tech CL 1B – This plugin is modeled after the classic Tube-Tech CL 1B hardware compressor and is available for $279 on the Softube website.
Waves SSL G-Master Buss Compressor – This plugin is modeled after the SSL G Series bus compressor and is available for $349 on the Waves website.
FabFilter Pro-C – This plugin is a versatile compressor that offers a wide range of features and is available for $179 on the FabFilter website.

If you’re interested in learning more about these plugins and others, check out the manufacturers’ websites:

Universal Audio: https://www.uaudio.com/
Waves: https://www.waves.com/
Softube: https://www.softube.com/
FabFilter: https://www.fabfilter.com/

Compressor/Limiter Setup

How to setup for Dynamics Control during Recording?

When setting up a compressor/limiter for dynamics control during recording, it’s important to consider the source material and the desired outcome. For example, if recording a singer, it may be necessary to use a high-pass filter to remove unwanted low-frequency noise. Additionally, it may be necessary to adjust the attack and release times to achieve the desired amount of compression.

How to setup for Voice-Overs during Recording?

When setting up a compressor/limiter for voice-overs during recording, it’s important to consider the desired outcome. A fast attack time and a high compression ratio may be necessary to prevent peaks and ensure consistent levels.

The two most important settings:

The two most important settings when setting up a compressor/limiter are the timing of attack and release, and the amount of compression. It’s important to experiment with these settings to achieve the desired sound.

Step-by-step recommendation for setting up and adjusting

Start with the threshold control set to 0 dB.
Adjust the attack time to achieve the desired amount of transient control.
Adjust the release time to achieve the desired sound.
Adjust the compression ratio to achieve the desired amount of compression.
Use the makeup gain control to compensate for any volume loss due to compression.

Conclusion

Compressor/limiters are an essential tool in the recording and mixing process. By understanding their primary controls, types, famous models, and setup, you’ll be able to achieve the desired sound for any recording or mixing project.