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JOEL JOHNSON

JOEL JOHNSON

Gear Highlights – Manley Variable Mu – BLOG
The MANLEY VARIABLE MU® LIMITER COMPRESSOR has been the best selling product for many years. It is one of the very few compressors that has become a real standard in Mastering studios and contributed to most hit records over the last decade and probably the next. “Mu” is tube-speak for gain, and Variable Mu® is our registered trademark for this limiter compressor. It works by using the “remote cut-off” or re-biasing of a vacuum tube to achieve compression. The precious vintage Fairchild 670 also uses this technique and is one of few all-tube compressors to do so that we know of. Even the side-chain has glowing rectifier bottles. 

"…a smooth ‘creme fraiche’ valve distortion…push it harder and you get plenty of punch, subjectively far more than meters would indicate, and the Manley begins to impress in a different way."

- Studio Sound, February 1997
manley vari

Gear Highlights – Manley Variable Mu -Blog
The renowned Manley Stereo Variable Mu 2-channel limiter/compressor is a favorite of producers and recording engineers — and one listen to what this remarkable all-tube, transformer-coupled device does for your sound will make you a believer, too! Anyone who has heard the classic Fairchild 670 limiter in action has an inkling of the Variable Mu’s capabilities, but the sound is even sweeter with the Variable Mu. Its adjustable threshold, attack, and release settings are ideal for tracking, mixing, and mastering; while its highpass sidechain gives you added flexibility. The Manley Variable Mu is a high-end, esoteric piece of kit that delivers miraculous results on individual tracks, stems, and full stereo mixes. It’s also incredibly versatile and rock-solid reliable for daily use. A modern all-American legend, the Variable Mu fortifies your mixes with glue and punch, crystallizing them into a professional, radio-ready product that blasts right out of the speakers. Add one to your studio rack, and hear what you’ve been missing!


The MANLEY VARIABLE MU® LIMITER COMPRESSOR has been the best selling product for many years. It is one of the very few compressors that has become a real standard in Mastering studios and contributed to most hit records over the last decade and probably the next. “Mu” is tube-speak for gain, and Variable Mu® is our registered trademark for this limiter compressor. It works by using the “remote cut-off” or re-biasing of a vacuum tube to achieve compression. The precious vintage Fairchild 670 also uses this technique and is one of few all-tube compressors to do so that we know of. Even the side-chain has glowing rectifier bottles.

How’s it work? The unique 5670 dual triode is at the center of the peak-reducing and compression action constantly being re-biased by the vacuum tube rectified side-chain control voltages which cause this tube to smoothly change its gain. Just like that.

The COMPRESS mode is soft-knee 1.5 to 1 ratio while the sharper knee LIMIT mode starts at 4 to 1 and moves to a more dramatic ratio of 20 to 1 when limiting over 12dB. Interestingly, the knee actually softens as more limiting is used. Distortion can be creatively used by turning up the Input and turning down the Output while using very little or no compression. See the gain reduction curves here!

You might notice that the Variable Mu® Limiter Compressor has a ganged input control, but do not jump to conclusions that it is mono-unfriendly. Track away! There are separate threshold and output controls to make compensations with plus you can always adjust your individual source levels elsewhere, right? The advantage of the stereo input control becomes dramatically clear when you switch to LINK mode, and that’s what our Variable Mu® Limiter Compressor does better than anything else: final mix, 2-track, or mastering limiting and compression. Like one reviewer put it: “It’s like pouring a bowl of sweet cream over the mix.” Mmmmmm. Yummy. Give your music a big hug.

A modern all-American legend

Although the Variable Mu is not a clone of one, the Fairchild 670 series used a similar operational principle and engineers at Sweetwater who have used that legendary unit know this method to be very special. With “mu” meaning gain or amplification factor, the Variable Mu offers true variable gain, unlike most compressor/limiters. How it works is that the 5670 dual triode is at the core of the peak-reduction action as it is constantly re-biased by the tube-rectified sidechain control voltages. This causes the tube to smoothly change its gain, and is responsible for the Variable Mu’s unique and highly effective gain reduction behavior, which gives you maximum level control with minimal artifacts.

From light leveling to heavy limiting

The Variable Mu’s Compress mode is a soft-knee 1.5:1 ratio while the sharper knee Limit mode starts at 4:1 and moves to a more dramatic ratio of 20:1 when limiting over 12dB. Interestingly, the knee actually softens as more limiting is used. Distortion can be creatively employed by turning up the Input and dialing down the Outputs while using very little or no compression.

Perfect for dual-mono or stereo applications

You might notice that the Variable Mu has a ganged input control, but it’s certainly not mono-unfriendly. There are separate threshold, attack, release, and output controls to make compensations with, plus you can always adjust your individual source levels elsewhere. The advantage of the stereo input control becomes clear when you switch to Link mode. And that’s where the Variable Mu excels — on stereo buses and for mastering your final mixes. As one reviewer put it: It’s like pouring “sweet cream” over your mix!

Get in touch!

If you guys have another other questions you would like to shoot at me, just shoot me a mail at ronak@gray-spark.com.
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