UAD Plug-Ins

Welcome to UA Support
How can we help?

Manley Variable Mu Manual

In this article

Tube compression royalty for your mixes

As Manley Labs' flagship compressor since 1994, the Variable Mu is a tube and transformer-driven classic that exudes hand-made craftsmanship. A gold standard among mixing and mastering engineers, the Variable Mu adds clarity and cohesion to stereo buses or your entire mix.

Developed under Manley Labs' rigorous scrutiny, the Manley Variable Mu Limiter Compressor plug-in is a thorough emulation of this legendary tube limiter, and is based on the coveted "6BA6 T-BAR Tube Mod" unit. Now, its famed sound is available exclusively for UAD.

  • Add definition and fidelity to individual tracks, stereo buses, or an entire mix

  • Glue together difficult mixes with signature Manley tube compression

  • Link channels for a precise, perfectly matched stereo image

  • Select from Left/Right or Mid/Side operation for precise control of stereo imaging

  • Use the plug-in-only Dry/Wet Mix control to easily dial-in parallel compression

Manley Variable Mu® Under the Hood

While the Manley Variable Mu uses the remote cut-off style gain reduction found in the Fairchild and other classic limiters, it has a sound and character all its own. Its classic dual-triode gain reduction design is constantly re-biased by the sidechain control voltages, creating a unique variable gain compressor with stunning transparency. This lets you treat source material with velvety-smooth gain reduction, while infusing warm harmonic content, free of audible compression artifacts.

King of the 2-Bus

The Manley Variable Mu Limiter Compressor plug-in can be used on single instruments such as bass or a lead vocal, or on subgroups like strings or horns. But its raison d'être is on the mix bus, where its expert features can unify your mixes with a rich, hi-fi fit and finish.

Powerful Controls

Parameter linking allows simultaneous adjustment of both channels with stereo signals. When unlinked, the plug-in's digital implementation of Mid/Side processing is actually improved over the hardware, providing phase accurate stereo imaging.

The High Pass Sidechain filter prevents compression response to frequencies lower than 100 Hz — letting you compress overheads, for example, while retaining powerful, punchy bottom-end.

Plug-in-only controls such as Dry/Wet Mix and Headroom give you more colors with which to paint your mixes. Dry/Wet Mix offers easy parallel compression — perfect for quickly polishing background vocals or a drum bus. Finally, the Headroom control lets you optimize the Variable Mu's overall level to your playback system.

Manley-Variable-Mu.png

Manley Stereo Variable Mu Limiter Compressor

 


 

Variable Mu Overview

The Manley Stereo Variable Mu Limiter Compressor is a highly flexible two-channel processor for adding transparent dynamics control and tube warmth to mix and master buses or individual tracks.

While the Manley Variable Mu uses the remote cut-off style gain reduction found in the Fairchild and other classic limiters, it has a sound and character all its own. Incorporating a traditional dual-triode gain reduction design which is constantly re-biased by the sidechain control voltages, the Variable Mu combines Manley's hand-selected tubes and in-house transformer manufacturing to create a unique variable gain compressor design with stunning transparency. This lets you treat source material with velvety-smooth gain reduction, while infusing warm harmonic content, free of audible compression artifacts.

Dual Mono/Stereo Processing

The Manley Variable Mu can operate in stereo or as a dual-mono device.

Dual Mono

When set to Left-Right (versus Mid-Side) and the sidechain is unlinked, the processor operates as a dual mono device. Except for the ganged Dual Input control, the left and right channels are completely independent, and each channel can have unique settings.

Stereo

When set to Left-Right and the sidechain is linked, the plug-in is operating as a stereo device. The left signal is fed to the left channel compressor, and the right signal is fed to the right channel compressor. The two compressors are constrained so that they both compress the same amount at any instant, preventing transients that appear only on one channel from shifting the stereo image of the output (any big transient on either channel will cause both channels to compress). The amount of compression will be similar to the amount of compression for a transient which appears on both channels at the same time.

In stereo operation, the controls for the left and right channels can be unlinked so they are independent and can be adjusted separately. Threshold, attack, and recovery can be set independently to cause the compressor to be more sensitive to instruments which are panned to one side or the other. Output controls can be set separately in order to correct an overall image shift at the output.

Mid-Side Processing

The Manley Variable Mu can perform dynamics processing on the middle and side components of stereo signals independently. In other words, the monophonic (middle, or sum) and/or stereo (side, or difference) components of a stereo source signal can be processed separately from the other component.

Mid-Side processing is accomplished by first routing the stereo source signal through a sum/difference matrix on input which separates a stereo source signal into its mono and stereo signal components. The mid-side components are then compressed or limited independently. Finally, the mid-side components are recombined into a normal stereo signal via another sum/difference matrix on output.

In the Variable Mu, the left+right (sum) middle signals are routed to the left channel, and the left-right (difference) side signals are routed to the right channel. The two channels can work independently of each other, or the dynamics sidechain control signal can be optionally linked for creative uses.

The Variable Mu has separate Mid-Side switches for input and output. The M-S IN switch activates the sum/difference matrix on input (encode) and the M-S OUT switch activates the sum/difference matrix on output (decode). The separate matrices allow for using only "half" of a full encode/decode circuit on input or output (but not both) when a full encode/decode process is not desired. For example, this feature can be used to decode stereo tracks recorded with the mid-side microphone technique back into a standard left/right stereo signal.

Note: Each sum/difference matrix simply inverts the stereo signal type from left-right to mid-side, or from mid-side to left-right. They don't distinguish between the original signal type, so they can be used to convert either type to the other type.

Variable Mu Modes

There are two independent processors within the Variable Mu. Depending on the state of the two Left-Right/Mid-Side switches (one for input and one for output) and the Sidechain Link switch, numerous operating modes are possible.

The switch positions required for various operating modes are shown in the table below, followed by descriptions of the modes.

Variable Mu Modes Table

Input Matrix

Output Matrix

Sidechain Link

Operating Mode

L-R

L-R

Unlinked

Dual Mono

L-R

L-R

Linked

Stereo Left/Right

M-S

M-S

Unlinked

Stereo Mid/Side (encode+decode)

M-S

L-R

Unlinked

Stereo Mid/Side (input matrix only)

L-R

M-S

Unlinked

Stereo Mid/Side (output matrix only)

Mode Descriptions

Dual Mono

In dual mono mode, the Variable Mu operates as two separate monophonic dynamic 
processors with independent control of the left and right channel signals. There is no interaction between the two processors.

Stereo Left/Right

In this mode, the Variable Mu operates as a typical stereo dynamics processor. The dynamics control signal sidechain of the two compressors are linked so that they both compress the same amount at any instant, preventing transients which appear on only one channel from shifting the stereo imaging of the output.

Dual Mid/Side (encode+decode)

In this mode the Variable Mu operates as two monophonic processors with independent control of the middle and side components of the two input signals. The input signals are encoded by the mid/side (sum/difference) matrix before processing and there is no interaction between the two processors. The left channel processes the mid component, the right channel processes the side component, and the mid/side components are decoded back into a normal stereo signal at the outputs.

Dual Mid/Side (input matrix only)

This mode is the same as Dual Mid/Side, except the signal components are not routed through the output matrix.

Dual Mid/Side (output matrix only)

This mode is the same as Dual Mid/Side, except the signal components are not routed through the input matrix.

Operating Headroom

The Headroom control, which is a UAD-only feature not found in the original hardware, enables adjustment of the internal operating reference level for the Manley Variable Mu. Headroom enables best practice operating level matching, or it can be used creatively 
to expand the sonic range of the processor. By fine-tuning Headroom, the non-linear I/O 
distortion and compression response characteristics can be tailored independently of signal input levels.

By increasing the Headroom (by rotating the control counter-clockwise), signals at the input can be pushed higher before they compress. For complete details about this feature, see Headroom.

Unmarked Controls

Some continuous controls (Dual Input, Threshold, Attack, Output) have a range of zero to ten when viewed in controls mode (if supported by the DAW). As with the original hardware, these controls are not marked with absolute values and are designed to be set "by ear" instead of by selecting pre-defined values.

Artist Presets

The Manley Variable Mu includes artist presets from prominent Variable Mu users. The artist presets are in the internal factory bank and are accessed via the DAW application's preset menu. The artist presets are also copied to disk by the UAD installer so they can be used within Apollo's Console application. The presets can be loaded using the Settings menu in the UAD Toolbar.

 


 

Manley Variable Mu Controls

Dual Input

This continuously variable control determines the signal input level (gain) for both channels of the processor. Higher levels result in a more colored signal. Lower levels result in a more transparent or natural sound.

Threshold

This continuously variable control determines the amount of compression to be applied to the channel. Rotate Threshold towards MIN (counter-clockwise) to lower the threshold and increase compression.

Tip: Signals below the threshold are not compressed.

Input Gain versus Threshold

The amount of signal compression is determined by both the Dual Input and Threshold controls. If one is increased and the other decreased, the compression characteristics won't change much, but the color characteristics will.

Tip: For less color with the same amount of compression, lower the input gain and lower the threshold control.

Attack

Attack sets the amount of time that must elapse once the input signal reaches the Threshold level before compression is applied. The faster the Attack, the more rapidly compression is applied to signals above the threshold.

The Attack range is continuously variable from 70 milliseconds (when set to SLOW) to 25 milliseconds (when set to FAST).

Recovery

The Recovery (release) knob sets the time it takes for processing to cease once the input signal drops below the threshold level. The available values are shown in the table below. The default setting is Medium Fast.

Recovery Knob Values

Knob Value

Time (seconds)

Slow

8

Medium Slow

4

Medium

0.6

Medium Fast

0.4

Fast

0.2

Output

Output provides continuous attenuation of the Variable Mu's signal level at the output of the plug-in. Note that output adjustment is only possible when the In/Bypass switch is set to In.

Note: This control has no effect on the dry signal component.

Compress/Limit

The Compress/Limit switch sets the channel to function as a limiter or a compressor.

Tip: For limiting or compression to occur, signal levels must exceed the Threshold value.

Limit

When set to Limit, the ratio starts at 4:1 and moves up to 20:1 when limiting exceeds 12 dB. The limiter provides a sharper knee to catch peaks, but actually softens as more limiting is used.

Compress

When set to Compress, the ratio is set to 1.5:1 with a soft-knee characteristic. Soft-knee provides a more subtle compression resulting in a natural, less compressed sound.

Note: As with the original hardware, the Variable Mu plug-in can never achieve greater than -10 dB of gain reduction.

Sidechain Filter

When set to HP SC, this switch rolls off low frequencies in the dynamics control sidechain. The signal is attenuated by -3 dB at 100 Hz with a slope of 6 dB per octave. When set to FLAT, the sidechain is unfiltered. The default setting is FLAT.

Removing low-frequency content from the sidechain by engaging the filter can reduce excessive gain reduction and/or "pumping" on bass-heavy audio signals without reducing bass content of the audio signal itself.

Bypass

The Bypass switch determines whether or not the incoming signal is processed by the plug-in. When set to Bypass, the source signal is unaffected.

Mid-Side/Left-Right

Note: For an overview of this feature, see Mid-Side Processing.

These two switches enable the sum/difference matrix for the input and/or the output. The switch on the left (labeled IN) enables the processor input matrix, and the switch on the right (labeled OUT) enables the processor output matrix.

  • For mid/side compression on a standard stereo left-right signal, set both IN and OUT switches to M-S.

  • For single-ended processing (for example, to process a stereo track recorded with a mid/side microphone technique), set only one switch to M-S.

  • Sidechain Link should generally be disabled for traditional mid-side processing. Of course, the sidechains can be linked for creative purposes.

IN

When the M-S switch labeled IN is set to L-R, incoming stereo signals are passed directly into the compressor inputs, bypassing the input sum/difference matrix.

When set to M-S, incoming stereo signals are passed through the sum/difference matrix, converting one signal type (left/right or mid/side) to the other type before compression.

OUT

When the M-S switch labeled OUT is set to L-R, outgoing (post-compression) stereo signals are passed directly to the outputs, bypassing the output sum/difference matrix.

When set to M-S, outgoing stereo signals are passed through the sum/difference matrix after compression, converting one signal type (left/right or mid/side) to the other type before being output.

Sidechain Link

When this control is set to Link, it causes the two channels of the compressor to compress in equal amounts. This does not mean that the compressor will be equally sensitive to either channel however; that depends on the settings of the other controls.

When Sidechain is set to LINK but Controls Link is off, the Threshold controls can be set independently to cause the compressor to be more sensitive to instruments which are panned to one side or the other. Output controls can be set separately in order to correct an overall image shift at the output.

Controls Link

This switch links the controls for the left and right channels of the processor. When set to LINK, adjusting the left channel controls will force the equivalent right channel controls to move to the same position.

To read and write automation data for both channels independently when in dual-mono mode, Controls Link must be disabled.

Important: When unlink is switched to link, the left channel values are copied to the right channel, and any control offsets between channels are lost.

Mix

The output balance between the signal processed by the plug-in and the original dry source signal can be adjusted with the Mix control. Mix facilitates parallel compression techniques without having to create additional routings in the DAW.

When set to DRY, only the unprocessed source signal is output. When set to WET (the default value), only the processed signal is output. When set to the center position (50%), an equal blend of both the dry and wet signals is output. The balance is continuously variable throughout the control range.

Note that the dry signal is unaffected by the Variable Mu's Output control.

Tip: Click the "MIX" text label to set the control to the 50% position. Click the "DRY" text label to set the control to the minimum position. Click the "WET" text label to set the control to the maximum position.

Headroom

The Headroom control is provided to allow best practice operating levels and accommodate applications where high amounts of gain reduction are not desired. Headroom simply changes the internal operating level so that the plug-in is not "pushed" into gain reduction as much.

Note: There is only one headroom parameter. Although the Headroom control appears twice in the Variable Mu window, they are permanently linked.

Headroom can be set (in dB) to 4, 8, 12, 14, 16, 18, 20, 24, or 28. The default value is 16 dB (when the set screw "dot" is in the straight up 12 o'clock position). Note that Headroom is increased as the dB value decreases.

Tip: Click the "HEADROOM" text label to return the control to the default value.

At higher dB values (clockwise rotation), signals will push the plug-in into gain reduction (and more non-linearity and "good" harmonic distortion color) more easily. Set the control to a lower value (counter-clockwise rotation) when less gain reduction and less color is desired.

Note: To avoid the temporary gain increases that can result when adjusting Headroom, automating this control is not recommended.

Keep in mind there are no hard and fast headroom rules. Feel free to experiment with the various positions of the Headroom control regardless of the audio source. If it sounds good, use it!

On/Off

This switch determines whether the plug-in is active. When set to the Off position, the VU meters go dark to indicate signal processing has ceased. In this state, plug-in processing is disabled and UAD DSP usage is reduced (unless UAD-2 DSP LoadLock is enabled).

Gain Reduction Meters

Dual VU meters display the amount of gain reduction in decibels. In typical use, adjusting Threshold towards MIN (counter-clockwise) results in the VU meters displaying higher amounts of reduction.

 


 

Additional Information

The original user manual written by Manley Labs for the hardware unit contains a wealth of great information about the philosophy, design decisions, and use of the Massive Variable Mu. It is highly recommended reading for those interested in technical details. The manual can be found on the Manley website, along with info about their other great products.

www.manley.com

Manley-Variable-Mu-HW.png

Original Manley Stereo Variable Mu Limiter Compressor hardware

 

manleylogo2013.png

All visual and aural references to the Variable Mu and all use of MANLEY's trademarks are being made with written permission from MANLEY LABORATORIES INCORPORATED. Special thanks to EveAnna 
Manley and Dave Collins.

Comments