Vari Mu Compressor – When to Use It in Your Mix

The Vari Mu compresser is one of four major types of audio compressors which can be used to reduce dynamic range. This allows you to achieve a more practical level for a track, impart more energy to that track, or simply have it more up front in the mix. Let’s talk about what exactly a vari mu compressor is, how it differs from other compressors, and most importantly when and how to use a vari mu compressor in your mix.

Vari Mu Compressor

vari mu compressor

Let’s begin by identifying what a vari mu compressor even is.

What is a Vari Mu Compressor

Vari mu is short for variable mu compressor, and it’s among the oldest types of compression. Mu is a Greek letter which in an engineering context refers to gain, so essentially variable mu just means variable or varying gain.

Based on vacuum tubes, the vari mu compressor alters the signal’s voltage to vary/control the gain. This brings a warm saturation sound to whatever you’re compressing with it.

The vari-mu style Fairchild 670 was released in 1959 and is considered to be the holy grail of analog/hardware based audio mixing equipment these days.

fairchild 670

Featuring 20 tubes and 11 transistors, the Fairchild 670 (by way of the mono 660) was actually designed from a request by Les Paul himself. Abbey Road purchased a dozen of the mono based 660’s in the early 1960’s, using them on vocals and Ringo’s drums on most of the Beatles releases.

When to Use a Vari Mu Compressor

History aside, when is it practical to use a vari mu compressor in your mix?

A vari mu compressor is slower than say a FET compressor or VCA compressor so it shouldn’t be your first choice when you need to get some fast peaks under control.

Vari mu compressors are best served when applied to a drum bus, vocal bus, or even on your master fader. Just note that you will get some of the saturation like distortion from the tube sounds, so it’s not a transparent compression in that sense.

When you want to impart a little bit of that warmth to a mix bus, a vari mu fills that role nicely.

Best Vari Mu Compressor

Waves PuigChild Compressor – I referenced the Fairchild 670 earlier; it was the gold standard in its day and modern day software based vari mu compressors are still based on it. Check out Waves’ PuigChild Compressor when you want to rein in a track or bring some cohesion to a bus with a little old fashioned tube style distortion on it.

vari mu compressors

As you can see from the design, it’s even visually inspired by the Fairchild.

A plugin I typically like to pit against it in a shootout particularly on my master bus (which I also mentioned as my favorite VCA compressor) is the SSL G Master Buss Compressor. I set each one up, A/B split test them, then take the winner.

Free Vari Mu Compressor

Klanghelm MJUC Jr. – The relative simplicity of Jr.’s input and output compared to the premium version of this plugin makes it hard to mess up while still giving you a nice warm fatness for bringing a little control to a drum or master bus.

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