Top 11 Best Variable-Mu Compressor Emulation Plugins In 2021


We’re currently living in the age of digital audio, and in-the-box mixing within a digital audio workstation is commonplace. Plugins are, therefore, invaluable assets for the modern audio engineer. There are plenty of plugins that aim to emulate analog hardware in an attempt to make digital audio sound more like its [arguably] nicer-sounding analog counterpart.

There are plenty of excellent analog variable-mu/tube compressors and plugin emulations of such compressors. With so many options to choose from, I’ve compiled what I consider to be the 11 best variable-mu/tube compressor emulations plugins.

What is a variable-mu compressor? A variable-mu (variable gain) compressor is an analog compressor centred around a vacuum tube. As the input signal increases, the current sent to the grid of the tube decreases, which results in a reduction in the overall level.

For more information on variable-mu/tube compressors, check out my article What Is A Variable-Mu (Tube) Compressor & How Does It Work?

The top 11 best variable-mu/tube compressor emulation plugins for digital audio workstations are:

  1. Arturia Comp Tube-STA
  2. Softube Summit Audio TLA-100A
  3. Klanghelm MJUC
  4. Pulsar Audio Mu
  5. Waves PuigChild 670
  6. IK Multimedia T-RackS 5 Dyna-Mu
  7. United Plugins Royal Compressor
  8. Native Instruments Vari Comp
  9. Slate Digital FG-Mu
  10. IK Multimedia T-RackS Vintage Compressor
  11. Universal Audio Fairchild 660 | 670

It should go without saying that any “top X” article is subject to bias. I would expect the next person’s top 11 to be different than mine but hope that there would be plenty of overlap.

That being said, I believe these plugins to be the best variable-mu/tube compressor emulation plugin options today. The criteria I used to judge these plugins include the following:

  • Sonic performance: how does the variable-mu compressor emulation plugin sound subjectively/objectively?
  • Graphic user interface (GUI): how does the variable-mu compressor emulation plugin look when loaded in the DAW?
  • Ease-of-use: how user-friendly is the variable-mu compressor emulation plugin?
  • Functionality: how many different functions does it serve and/or how many parameters are available for the variable-mu compressor emulation effect?
  • Accessibility/compatibility: how easy is it to acquire the variable-mu compressor emulation plugin, and what are the system requirements?

Let’s discuss each of the top 11 best variable-mu/tube compressor emulation plugins in greater detail to learn why they made this list.


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Arturia Comp Tube-STA

The Arturia Comp Tube-STA (link to check the price at Plugin Boutique) is a plugin emulation of the original Gates STA-Level Tube Compressor.

Arturia Comp Tube-STA

The Arturia Comp Tube-STA is compatible with Mac OS and Windows OS and comes in AAX, AU and VST formats.

Arturia’s Comp Tube-STA is a superb digital plugin recreation of a truly spectacular all-American tube compressor. Featuring simple controls and flexibility in performance, this compressor plugin captures the beautiful vintage tone of the original in an easy-to-use plugin format.

Thanks to the power of Arturia’s exclusive TAE® modelling technology, this compressor plugin maintains the familiar and forgiving non-linear attacks and release times. Its harmonically rich sound works fabulously on practically any source material.

The simple controls of the Arturia Comp Tube-STA include Input and Output levels with input-output link control, Mode and Recovery Time controls (to adjust both attack and release times) and Meter selection (Input, Output or Gain Reduction levels). The top panel also offers a Mix control for easy parallel compression.

Arturia also includes other parameters not featured in the original hardware in the bottom panel.

This bottom panel hosts the advanced sidechain control and equalizer. Choose between internal and external sidechain signals and control the gain of the sidechain easily. The detection mode offers 5 different methods of reading the sidechain signal. Select from Reversed, Dual (left + right channels), Linked, Mid Only or Side Only modes.

Use the three-band semi-parametric EQ to shape the sidechain signal to enhance the compression triggering and achieve de-essing.

To learn more about compressor sidechain signals and semi-parametric EQ, check out the following My New Microphone articles:
The Complete Guide To Sidechain Compression In Audio
 What Is Semi-Parametric Equalization/EQ In Audio?

From subtle overtones and gentle tone shaping to distinctly analog soft-clipping saturation, the Arturia brings the sound of the famed Gates STA-Level Tube Compressor to the world of audio plugins.

For more information on system requirements and authorization instructions, check out the Comp Tube STA user manual.

Arturia is featured in the following My New Microphone articles:
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Softube Summit Audio TLA-100A

The Softube Summit Audio TLA-100A (link to check the price at Plugin Boutique), as the name would suggest, is a plugin emulation of the superb Summit TLA-100A Tube Leveling Amplifier.

Softube Summit Audio TLA-100A

The Softube Summit Audio TLA-100A is compatible with Mac OS and Windows OS and comes in AAX, AU and VST formats.

Softube has done tremendous work modeling gentle, natural-sounding gain reduction and sublime leveling of the user-friendly TLA-100A. This plugin sounds amazing on pretty much everything, offering seemingly effortless control over signal dynamics without flattening the sound.

Officially licensed and created in partnership with Summit Audio, this Softube plugin is about as close as you’ll get to this world-renowned hardware compressor without having to buy one for yourself. This plugin offers some of the best-emulated variable-mu/tube compression available from the sonic character and controls to the user interface itself.

This program-dependent compressor practically does the job for you and offers soft and warm distortion if you drive it super hard. Adjust the Gain, Gain Reduction, and Attack and Release time parameters to your liking and enjoy the marvellous sound of this excellent variable-mu compressor plugin. Additionally, users can select between an interior or exterior sidechain signal.

To learn more about compressor attack and release parameters, check out my article Dynamic Range Compression: Attack & Release Controls.

With the limitless potential of plugin programmed, Softube has included additional controls over the original, including a Low Cut (High-pass) Filter, Saturation Knob, and Parallel Inject​.

To learn more about high-pass filters, check out my article Audio EQ: What Is A High-Pass Filter & How Do HPFs Work?

For more information on system requirements and authorization instructions, check out the Summit Audio TLA-100A at Softube.

Softube is featured in the following My New Microphone articles:
Top 11 Best Audio Plugin (VST/AU/AAX) Brands In The World
Top 11 Best DAW Control Surface Brands In The World


Klanghelm MJUC

The Klanghelm MJUC (link to check the price at Klanghelm) actually has three different models of variable-mu-style compression.

Klanghelm MJUC

The Klanghelm MJUC is compatible with Mac OS and Windows OS and comes in AAX Native, AU and VST formats.

Klanghelm’s MJUC is an ultra-versatile variable-mu compressor plugin. With extensive research and development spanning practically all variable-mu compression implementations, the MJUC has been ultimately developed with 3 distinctly magnificent tube-compressor algorithms.

The sonic diversity of variable-mu compressor topologies is on full display with this superb plugin. Let’s quickly describe the 3 models.

The Klanghelm MJUC Mk 1 is based on early variable-mu designs from the 1950s. Its compression sound very natural due, in large part, to the emulated high control voltage and simple signal path.

The Klanghelm MJUC Mk 2 is based on the more involved designs of the 175 and 176 from the early 1960s. This model features 4 ratios and a second gain reduction stage to reduce the program dependence of the compression circuit. A density switch and interstage transformer can be engaged to thicken the sound and reduce overall noise and distortion, respectively. The harmonic distortion of the Mk 2 is a bit more than the Mk 1.

The Klanghelm MJUC Mk 3 is based on a modern interpretation of the variable-mu technology modelled on differential circuitry, making the unit very quiet and almost distortion-free. It uses two distinct variable-mu stages (one in feed-forward and one in feedback topology) and is the cleanest model of the MJUC.

To learn more about feed-forward and feedback compressor topologies, check out my article Feedback Vs. Feed-Forward Dynamic Range Compressors In Audio.

Each of the MJUC’s models has its own signal path and dedicated controls. Use the Timbre knob to shape the tone of each model. The Drive control adjusts the load of the virtual input and output transformers and the saturation of the tube gain stages, thereby warming up the sound of this awesome vari-mu plugin.

For more information on system requirements and authorization instructions, check out the Klanghelm user manual.


Pulsar Audio Mu

The Pulsar Audio Mu (link to check the price at Plugin Boutique) is a plugin emulation of the legendary Manley Variable Mu compressor, which is a modern emulation of the iconic Fairchild 660 tube compressor.

Pulsar Audio Mu

The Pulsar Audio Mu is compatible with Mac OS and Windows OS and comes in AAX, AU and VST formats.

This plugin is a remarkably faithful emulation of the 660 and works tremendously well for mixing and mastering. With the exceptional compression transparency of the original, Pulsar Audio’s Mu is a top performer when it comes to variable-mu compressor plugin emulations.

Thanks to Pulsar Audio’s unique Topology Preservation Technology, the company has been able to model the precise characteristic of the 660 and even exceed the performance of the original with improved noise specifications. With stereo functionality, the Mu may be considered closer to the 670 (the stereo version of the Fairfield 660), though the modelled has been specifically done on the 660.

In addition to the left/right stereo mode, Pulsar Audio’s Mu also offers mid/side operation. The accurate SIFAM metering is superb. The plugin even has a more modern visualization mode for fine-tuning compression settings, representing the waveform and gain reduction over time and instantaneously.

This plugin also offers superior control over the sidechain signal. The Pulsar Mu pushed the popular high-pass modification in the sidechain signal even further with an all-new EQ section featuring 3 EQ bands with variable frequencies (high-pass, mid-peak and high-shelf). Lookahead and look-behind features are also made available for improved control over transients.

To learn more about compressor lookahead, check out my article Dynamic Range Compression: What Is The Lookahead Control?

Whether the compression task on a drum bus, acoustic guitar, vocal, snare drum or even the master channel, you can count on the Pulsar Audio Mu to deliver transparent yet warm results we have come to expect from world-class variable-mu compressors.

For more information on system requirements and authorization instructions, check out the Mu user manual.


Waves PuigChild 670

The Waves PuigChild 670 (link to check the price at Waves Audio) is a plugin emulation of the highly coveted stereo Fairchild 670. More specifically, it’s modelled after the 670 of Grammy-winning producer/engineer Jack Joseph Puig as part of Puig and Waves’ partnership.

Waves PuigChild 670

The Waves PuigChild 670 is compatible with Mac OS and Windows OS and comes in AAX, AU and VST formats.

Waves is well known for its outstanding plugin emulations of world-class hardware. The original Fairchild 670 is a perfect example of the company’s dedication to precision-modelled plugins, carefully programmed to capture the distinctive nuance and harmonic detail of the vintage Fairchild 670 compressor housed in Jack’s own studio.

Each of the 20 vacuum tubes and 11 hand-wired transformers has been taken into account in this truly remarkable digital recreation of a classic. The PuigChild 670 presents the sonic character and performance of the hefty 65-pound 6 rack-space beast of a tube compressor in an easily accessible (and affordable) audio plugin.

The modelled high-control-voltage push-pull amplification stages recreate the beautifully natural style of compression of the original 670. Simple controls include input gain, threshold, time constant and output gain. The PuigChild 670 works in linked and unlinked stereo modes or lateral vertical mode (mid-side compression) for optimal stereo imaging.

For more information on system requirements and authorization instructions, check out the PuigChild user manual.

Waves Audio is featured in My New Microphone’s Top 11 Best Audio Plugin (VST/AU/AAX) Brands In The World.


IK Multimedia T-RackS 5 Dyna-Mu

The IK Multimedia T-RackS Dyna-Mu (link to check the price at B&H Photo/Video) is another emulation of the renowned Manley Variable Mu compressor.

IK Multimedia T-RackS 5 Dyna-Mu

The IK Multimedia T-RackS 5 Dyna-Mu is compatible with Mac OS and Windows OS and comes in AAX, AU, VST, RTAS and T-RackS CS Standalone formats.

This compressor plugin has a spectacular all-tube character, like the original hardware it emulates. The warm sound and expressive tone have been captured with stunning accuracy thanks to IK Multimedia’s virtual circuit modeling.

From mix buses to master channels to individual tracks, you can’t go wrong with the T-RackS 5 Dyna-Mu. The natural yet colourful tone offers superb glue compression and beautiful saturation when pushed hard.

Easy-to-use virtual knobs make adjusting the input level, threshold, attack, release and output level super simple. The ratio can be altered from a 1.5:1 to a 4:1 ratio when the Hard switch is disengaged and engaged, respectively.

To learn more about compressor threshold and ratio, check out the following My New Microphone articles:
Dynamic Range Compression: What Is The Threshold Control?
Dynamic Range Compression: What Is The Ratio Control?

In typical T-RackS fashion, The Dyna Mu is designed for operational mode with both L/R and M/S channels. Control both channels simultaneously with the Gang switch and choose linked or independent channel sidechaining with the Link switch. Like many modern compressors (and like a popular modification to the original), the Dyna-Mu features an optional high-pass filter in its sidechain signal path.

For more information on system requirements and authorization instructions, check out the Dyna-Mu specs at IK Multimedia.

IK Multimedia is featured in My New Microphone’s Top 11 Best Virtual/Software Instrument Plugin Brands.


United Plugins Royal Compressor

The United Plugins Royal Compressor (link to check the price at Plugin Boutique) is a super plugin based on the classic EMI RS124 Vari Mu style compressor of Abbey Road Studios fame.

United Plugins Royal Compressor

The United Plugins Royal Compressor is compatible with Mac OS and Windows OS and comes in AAX, AU and VST formats.

This variable-mu compressor plugin provides true vintage analog sound and feel. The United Plugins Royal Compressor sounds like the real deal, from the pleasing saturation to the gentle program-dependent compression.

The Royal Compressor actually offers 3 different circuit types, selectable via the A/B/C Model knob. All 3 models are strictly variable-mu emulations, though they are unique in their modelled circuitry and offer varying attack times.

Beyond the different models, this compressor is pretty straightforward in its control. Dial-in input levels, recovery (release) and output attenuation to get the desired amount of compression. Engage auto-gain for improved A/Bing and adjust the Saturation knob to get the perfect amount of vacuum tube warmth.

This beautiful plugin sounds great, looks great and runs on surprisingly little CPU, making it a deserving plugin for mix buses and, if necessary, every single track in a DAW session.

For more information on system requirements and authorization instructions, check out the Royal Compressor user manual.


Native Instruments Vari Comp

The Native Instruments Vari Comp (link to check the price of the Premium Tube Series at Native Instruments) is actually a collaborative effort between NI and Softube to create a plugin modelled after Manley’s Variable Mu compressor.

Native Instruments Vari Comp

The Native Instruments Vari Comp is compatible with Mac OS and Windows OS and comes in AAX, AU and VST formats.

Native Instruments makes superb virtual instruments and audio plugins, so it should come as no surprise to see the Vari Comp on this list. This all-purpose 2-channel compressor is super user-friendly and sounds incredible on individual tracks and buses alike. Transparent compression with subtle analog character is made simple with NI’s Vari Comp.

There are two modes with this compressor. The Compress (Comp) mode offers a subtle ratio of 1.5:1 and a notably transparent sound. The Limit mode makes the compressor even more program-dependent with a soft knee and ratio that ranges from 4:1 near the threshold to 20:1 at the extreme.

To learn more about compression knee, check out my article Dynamic Range Compression: What Is The Knee Control?

This compressor plugin offers a switchable high-pass filter in the sidechain (internal or external) signal path and simple parallel compression via the Dry knob.

For more information on system requirements and authorization instructions, check out the Vari Comp at Native Instruments.

Native Instruments is featured in the following My New Microphone articles:
Top 11 Best Virtual/Software Instrument Plugin Brands
Top 11 Best MIDI Controller Brands In The World

Manley Laboratories is featured in the following My New Microphone articles:
Top 11 Best Audio Compressor Brands In The World
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Slate Digital FG-Mu

The Slate Digital FG-Mu (link to check the price of the Virtual Buss Compressor Series at Slate Digital) is a tube compressor plugin based largely on the Fairchild 670 and Manley Vari Mu.

Slate Digital FG-Mu

The Slate Digital FG-Mu is compatible with Mac OS and Windows OS and comes in AAX, AU and VST formats.

Slate Digital’s FG-Mu is part of the Virtual Buss Compressors: a suite of 3 expertly modelled compressor plugins.

As mentioned, the FG-Mu is based on the Fairchild 670 and Manley Vari-Mu (note that the Manley Vari-Mu is, itself, based on the 670). Slate Digital has recreated the unique nonlinearities of the circuit paths with expert modelling techniques to give this tube/vari-mu compressor plugin its revered sound.

Dial-in the straightforward controls and hear the sound of the 670 and Vari-Mu clearly with this superb plugin. This is true with or without any gain reduction taking place. Smooth, warm, aggressive; whatever style of vari-mu compression you’re after, the FG-Mu has a preset for it.

For more information on system requirements and authorization instructions, check out the Virtual Buss Compressor webpage at Slate Digital.

Slate Digital is featured in My New Microphone’s Top 11 Best Audio Plugin (VST/AU/AAX) Brands In The World.


IK Multimedia T-RackS Vintage Compressor

The IK Multimedia T-RackS Vintage Compressor (link to check the price at Sweetwater) is yet another plugin emulation of the renowned Fairchild 670 compressor/limiter.

IK Multimedia T-RackS Vintage Compressor

The IK Multimedia T-RackS Vintage Compressor is compatible with Mac OS and Windows OS and comes in AAX, AU, VST, RTAS and T-RackS CS Standalone formats.

IK Multimedia T-RackS gets its second mention with this one. The Vintage Compressor gives users the classic Vari-MU dynamics of the beloved Fairchild 670 in a simple plugin format. Modelled right down to the 20 tubes, this plugin is a perfect representation of the original’s sound and character.

Like many top-of-the-line compressor emulation plugins, IK expanded on the functionality of the T-RackS Vintage Tube Compressor/Limiter, including options of Mid-Side processing on top of its standard 2-channel mode.

The plugin looks fantastic and offers the smooth levelling and powerful punch of the original dynamics processor

Unlike the previously-mentioned T-RackS plugin, the Vintage Compressor doesn’t include the standard “L/R-M/S” selector. Rather, this functionality is achieved via the original controls. The Left/Lateral and Right/Vertical switches to the left side of the interface make standard stereo operation and mid-side operation easily accessible.

For more information on system requirements and authorization instructions, check out the Vintage Compressor specs at IK Multimedia.


Universal Audio Fairchild 660 | 670

The Universal Audio Fairchild 660 | 670 (link to check the price at Universal Audio), as the name suggests, is a set of plugins that emulate the previously-discussed Fairchild 660 (mono) and 670 (stereo) variable-mu compressors.

Universal Audio Fairchild 660 | 670

The Universal Audio Fairchild 660 | 670, like all UAD plugins, requires UAD hardware to function with your DAW. UAD hardware is compatible with Mac OS and Windows OS, and the plugins are available in AAX, AU and VST formats.

Universal Audio has a knack for producing surprisingly perfect reactions of classic hardware in plugin form. This is certainly the case with the renowned Fairchild 660 & 670. The gold standard in vintage tube compression has been made available to the masses with astonishing precision.

After already having gone over multiple plugin emulations of this legendary hardware, there isn’t much else to say regarding the character and controls.

In addition to the original functionality, UAD includes a wet/dry mix control (for easy parallel compression), sidechain filters and headroom control, which helps tremendously in making mastering cleaner and individual tracks grittier (if that’s what you’re after).

Since UAD released its Fairchild 670 Legacy plug-in in 2004, the company has been known for making the best 670 emulations available. Today, this plugin sounds even more like the original and offers even more functionality, making it a top pick for this article, without a doubt.

For more information on system requirements and authorization instructions, check out the UAD Plug-Ins Manual.

Universal Audio is featured in the following My New Microphone articles:
Top 11 Best Audio Plugin (VST/AU/AAX) Brands In The World
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Top 11 Best Audio Compressor Brands In The World

Arthur

Arthur is the owner of Fox Media Tech and author of My New Microphone. He's an audio engineer by trade and works on contract in his home country of Canada. When not blogging on MNM, he's likely hiking outdoors and blogging at Hikers' Movement (hikersmovement.com) or composing music for media. Check out his Pond5 and AudioJungle accounts.

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