The UAD 4K Plug-Ins

This month we’re talking about the much-celebrated UAD 4K plug-ins: the UAD 4K Buss Compressor and the UAD 4K Channel Strip. And we’re also taking some time to tout the manual that is installed with the UAD software. The UAD manual is a PDF document that is loaded with a wealth of information about not only what a control does and why it does it, but also helpful hints and the history of the unit that we modeled. If you’re the kind of person that tends to just dive into a plug-in and use your ears right from the beginning, well then, more power to you! But even those users can find some golden nuggets of info in our expertly written manuals.

Our videos also strive to educate users about the plug-in, and cool ways to use it. So if you haven’t read about the UAD 4K plug-ins in the manual, or watched the videos, you may just learn something new about these emulations of the studio workhorses that still crank out hits to this day.

UAD 4K Buss Compressor

Large Format Console Dynamics
The SSL 4000 is famous as the console behind more Platinum records than any other, and the UAD 4K Buss Compressor emulates the console dynamics from the 4000 in all its hit-making glory. With its simple control set and wonderfully transparent compression characteristics, UA has captured this undisputed icon of record production with exacting accuracy. The UAD 4K Buss Compressor is a circuit emulation of the 4000 G+ and a companion to the UAD 4K Channel Strip.

The simple control set of the UAD 4K Buss Compressor comprises fixed Attack and Release controls with an Auto Release, which incorporates a program dependent response. Three fixed ratio settings are available: 10:1, 4:1 and 2:1. Continuous Threshold Control and Make-Up Gain round out the features, along with a compressor bypass.

Threshold
Threshold defines the signal level at which the onset of compression occurs. Incoming signals that exceed this level are compressed. Signals below the level are unaffected. The control range is ±15 dB.

As the Threshold control is decreased and more compression occurs, output level is typically reduced. Adjust the Make Up control to modify the output to compensate if desired.

Make Up
Make Up controls the signal level that is output from the plug-in. The range is 0 dB to +15 dB.

Generally speaking, adjust the Make Up control after the desired amount of compression is achieved with the Threshold and Ratio controls. Make Up does not affect the amount of compression.

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. Available attack times are discrete values of 0.1, 0.3, 1, 3, 10, and 30 ms.

The availability of relatively slow attack times (as compared to other compressors) is one factor that can provide the in-your-face, pumping quality that is so popular with large console VCA-style compressors.

Release
Release sets the amount of time it takes for compression to cease once the input signal drops below the threshold level. Slower release times can smooth the transition that occurs when the signal dips below the threshold, especially useful for material with frequent peaks. However, if you set the release time too long, compression for sections of audio with loud signals may extend to lengthy sections of audio with lower signals.

Available release times are discrete values of 100 ms, 300 ms, 600 ms, 1.2 sec., and Auto. The Auto release characteristic for the 4K Buss Compressor has a unique quality that is optimized for program material.

Ratio
Ratio defines the amount of gain reduction to be processed by the compressor. For example, a value of 2 (expressed as a 2:1 ratio) reduces the signal above the threshold by half, with an input signal of 20 dB being reduced to 10 dB. The available ratio values are 2:1, 4:1, and 10:1.

Power (IN)
The Power button determines whether the plug-in is active. Click the Power button to toggle the processor state. Power is useful for comparing the processed sound to that of the original signal.

Gain Reduction Meter
The Gain Reduction VU-style meter displays the amount of gain reduction occurring in the compressor. Higher values indicate more gain reduction.

Increase the signal level into the plug-in and/or lower the Threshold control to increase gain reduction.

An interesting article about the 4K Buss Compressor can be found in the "Ask The Doctors" section of the Universal Audio April 2009 WebZine.

UAD 4K Channel Strip

Large Format Mix Module
With its VCA compression characteristics ranging from transparent to in your face, and its intuitive, rich EQ with colorful band interdependencies, the UAD 4K Channel Strip faithfully emulates the console channel from the SSL 4000. The UAD 4K Channel Strip is an exacting circuit emulation of the 4000 G+, complete with the Type E "black knob" four-band EQ widely held to be the favorite in SSL's signal processing lineage.

A broad range of features complement the UAD 4K Channel Strip: 18 dB per octave high and 12 dB per octave low cut filters, independent expander/gate and compressor/limiter features, plus the famous Type E four-band EQ. The middle EQ bands are fully parametric, while the high and low bands provide the user with switchable bell or shelving filters. The Limit/Comp provides Threshold, a fixed fast or slow Attack time, a 100 ms to 4 sec. Release, and a continuously variable Ratio control. The gate/expander provides Threshold, a fixed fast or slow Attack time, a 100 ms to 4 sec. Release and Range to tailor the gate or expansion effect. In addition, the UAD 4K Channel Strip adds a second gate setting that incorporates a "no-chatter" gate circuit borrowed from later SSL designs.

The user may engage the Pre-Dyn button to reorder the signal chain so that the EQ is before the dynamics section. With the Dyn-Sc button, the user may engage a sidechain feature to achieve frequency-dependent compression using either the EQ, cut filters, or both. Lastly, the Link button adds the ability to have the sidechain linked or unlinked when using the stereo version of the plug-in.

The 4K Channel Strip controls are divided into four main sections: filters, dynamics, EQ, and global.

Note: SSL consoles adopt a different pan law than what the host application may be set to by default. Most DAWs allow configuring the panning spread preference to match various consoles. In the event you want to capture SSL-style stereo response when using multiple instances of the 4K Channel Strip, set the pan law preference in the host to a value of -4.5 dB.

Note: Knob settings, when compared to the graphical user interface silkscreen numbers, may not match the actual parameter values. This behavior is identical to the original hardware, which we modeled exactly. When the plug-in is viewed in parameter list mode (a.k.a. Controls Mode, not available in all hosts), the actual parameter values are displayed.

1. Filters

In addition to the four-band equalizer, UAD 4K Channel Strip offers individual high and low pass filters.

When the Filter control is at minimum value (fully counter-clockwise), the filter is disabled.

High Pass

The left knob determines the cutoff frequency for the high pass filter. Rotate clockwise to reduce low frequencies. The slope of the high pass filter is 18 dB per octave. The available range is 16 to 350 Hz.

Low Pass

The right knob determines the cutoff frequency for the low pass filter. Rotate clockwise to reduce high frequencies. The slope of the low pass filter is 12 dB per octave. The available range is 22 to 3 kHz.

Filters to Sidechain (DYN SC)

This button enables the Filters sidechain function. When the Filters sidechain is active, signal output from the Filters module is removed from the audio path and is instead routed to control ("key") the dynamics module.

Sidechaining is typically used for de-essing and similar frequency-conscious techniques. To listen to the sidechain key, simply disengage DYN SC to hear the filtered signal. The sidechain dynamics/EQ implementations are true stereo when used in a stereo in/stereo out ("SISO") configuration.

Note: The Filters module must be active (not at minimum value) in conjunction with the Filters DYN SC button for the Filters sidechain to function. An additional dynamics sidechain is available in the Equaliser section. (See EQ to Sidechain (DYN SC), below.)

2. Dynamics

Separate "soft-knee" compressor/limiter and expansion/gate modules are available in the dynamics section. Each module has their own set of controls.

Note: Dynamics are not processed unless enabled by the Dynamics selector buttons.

Compressor/Limiter Link

When UAD 4K Channel Strip is used in a stereo-in/stereo-out configuration, two separate dynamics processors are active (one for each stereo channel). When Link is engaged, the two compressors are constrained so that they both compress by the same amount at any instant.

This prevents 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.

Link is active when its amber LED is illuminated. When the plug-in is used in a mono-input configuration, Link has no affect.

Compress Ratio

Ratio defines the amount of gain reduction to be processed by the compressor. For example, a value of 2 (expressed as a 2:1 ratio) reduces the signal above the threshold by half, with an input signal of 20 dB being attenuated to 10 dB.

The UAD 4K Channel Strip compressor offers a continuously variable ratio between 1:1 (no compression) and infinity:1 (limiting).

Note: Signals must exceed the Threshold value before they are attenuated by the Ratio amount.

Compress Threshold

Threshold defines the signal level at which the onset of compression occurs. Incoming signals that exceed this level are compressed. Signals below the level are unaffected. The available range is +10 to -20 dB. Rotate the control clockwise for more compression.

This compressor has an automatic make-up gain function. As Threshold is lowered and compression increases (as knob is rotated clockwise), output gain from the module is increased automatically to compensate.

Compress Release
Release sets the amount of time it takes for gain reduction to cease once the input signal drops below the threshold level. Longer release times can smooth the transition that occurs when the signal dips below the threshold, which is especially useful for material with frequent peaks. However, if you set the Release time too long, the gain reduction imposed by loud sections of audio may initially reduce the level of subsequent sections of audio with lower signals.

Available Release times are continuously variable between 0.1 and 4 seconds.

Compress Attack
Attack defines the duration between the input signal reaching the threshold and processing being applied by the compressor. Attack time is normally auto-sensing and program dependent. When Fast Attack is enabled, attack time is 1 ms.

Fast Attack is active when the "F.ATT" LED is illuminated. To toggle Fast Attack, click the LED or its label text.

Gate/Expander
The gate/expander module operates in either gate or expansion mode, as determined by the Dynamics Select button. Two attack speeds and a continuously variable release time are available in both modes.

Dynamics Select
The Select button cycles through the three modes available in the gate/expander module: Expand, Gate 1, and Gate 2.

Expand (EX)
In Expand mode, the module applies downwards expansion at a fixed 1:2 ratio, with the amount of gain reduction determined by the Range control. (See Expand Range, below.)

Gate 1 (G1)
In Gate 1 mode, signals below the Expand Threshold are attenuated by the Expand Range amount. Gate 1 is authentic to the gate mode on earlier hardware consoles.

Gate 2 (G2)
Gate 2 mode operates the same way as Gate 1, but has a different "no-chatter" response characteristic that is derived from later versions of the hardware.

Expand Threshold
Threshold defines the input level at which expansion or gating occurs. Any signals below this level are processed. Signals above the threshold are unaffected. Threshold is continuously variable from -30 to +10 dB.

In typical use, it's best to set the threshold value to just above the noise floor of the desired signal (so the noise doesn't pass when the desired signal is not present), but below the desired signal level (so the signal passes when present).

Expand Range
Range (depth) controls the difference in gain between the gated/expanded and non-gated/expanded signal. Higher values increase the attenuation of signals below the threshold. When set to zero, no gating or expansion occurs. Range is continuously variable from 0 to -40 dB.

Expand Release
Release sets the amount of time it takes for gate/expander processing to engage once the input signal drops below the Threshold value. The available range is 0.1 ms to 4 sec.

Slower release times can smooth the transition that occurs when the signal dips below the threshold, which is especially useful for material with frequent peaks.

Note: Fast release times are typically only suitable for certain types of percussion and other instruments with very fast decays. Using fast settings on other sources may produce undesirable results.

Expand Attack
Attack defines the duration between the input signal reaching the threshold and processing being applied by the expander/gate. Attack time is normally auto-sensing and program dependent. When Fast Attack is enabled, attack time is 1 ms.

Fast Attack is active when the "F.ATT" LED is illuminated. To toggle Fast Attack, click the LED or its label text.

Dynamics Enable
These three buttons determine the status of the dynamics processors.

Dynamics In (DYN IN)
The DYN IN button enables both the compressor/limiter and the expander/gate modules; neither module will function when DYN IN is disabled. The dynamics modules are enabled when the green LED is illuminated.

DYN IN is useful for quickly comparing the original signal dynamics to the dynamically processed signal.

Note: DYN IN must be engaged to enable compressor/limiter and/or expander/gate processing.

Expander In (EXP IN)
The EXP IN button enables the expander/gate module. The module is enabled when the amber LED is illuminated. This button has no effect when DYN IN is disabled.

Compressor In (CMP IN)
The CMP IN button enables the compressor/limiter module. The module is enabled when the red LED is illuminated. This button has no effect when DYN IN is disabled.

Dynamics Meters
The Expansion Meter uses green LEDs (left column) to display the amount of downward expansion occurring in the expander/gate module. Higher values indicate more gain reduction.

The Compression Meter uses amber LEDs (right column) to display the amount of gain attenuation occurring in the compressor/limiter module. Higher values indicate more dynamics compression.

3. Equalizer

The UAD 4K Channel Strip equalizer module is divided into four frequency bands: High Frequency (HF, blue knobs), High Midrange Frequency (HMF, green knobs), Low Midrange Frequency (LMF, yellow knobs), and Low Frequency (LF, orange knobs). The high and low bands can be switched from shelving mode into bell (peak/dip) mode. The two midrange bands are fully parametric. The EQ module can be disabled altogether or routed for dynamics sidechain keying.

High Frequency (HF) Band

HF Gain

This control determines the amount by which the frequency value for the band is boosted or attenuated. The available range is ±15 dB.

Note: Click the "0" to return the Gain knob to its center position.

HF Frequency

This control determines the band frequency to be boosted or attenuated by the band Gain setting. The available range is 1.5 to 16 kHz.

HF Bell

The Bell button switches the HF band from shelf mode to peak/dip mode. In normal (shelf) mode, only frequencies above the frequency value are boosted or attenuated. In Bell (peak/dip) mode, frequencies above and below the frequency value are boosted or attenuated.

High-Mid Frequency (HMF) Band

HMF Gain

This control determines the amount by which the frequency value for the band is boosted or attenuated. The available range is ±15 dB.

Note: Click the "0" to return the control knob to its center position.

HMF Frequency

This control determines the HMF band center frequency to be boosted or attenuated by the band Gain setting. The available range is 0.6 to 7 kHz.

HMF Q

The Q (bandwidth) control defines the proportion of frequencies surrounding the band center frequency to be affected by the band gain control. The filter slopes get steeper (narrower bandwidth) as the control is rotated counter-clockwise. The available range is 0.4 to 4.

Low-Mid Frequency (LMF) Band

LMF Gain

This control determines the amount by which the frequency value for the band is boosted or attenuated. The available range is ±15dB.

Note: Click the "0" to return the control knob to its center position.

LMF Frequency

This control determines the LMF band center frequency to be boosted or attenuated by the band Gain setting. The available range is 0.2kHz to 2.5kHz.

LMF Q

The Q (bandwidth) control defines the proportion of frequencies surrounding the band center frequency to be affected by the band gain control. The filter slopes get steeper (narrower bandwidth) as the control is rotated counter-clockwise. The available range is 0.4 to 4.

Low Frequency (LF) Band

LF Gain

This control determines the amount by which the frequency value for the LF band is boosted or attenuated. The available range is ±15 dB.

Click the "0" to return the control knob to its center position.

LF Frequency

This control determines the band center frequency to be boosted or attenuated by the band Gain setting. The available range is 30 to 450 Hz.

LF Bell

The Bell button switches the LF band from shelf mode to peak/dip mode. In normal (shelf) mode, only frequencies below the frequency value are boosted or attenuated. In Bell (peak/dip) mode, frequencies below and above the frequency value are boosted or attenuated.

Equaliser Enable

These three buttons determine the status of the equalizer module.

EQ In

The EQ IN button enables the equalizer module. The EQ module is enabled when the green LED below the button is illuminated.

EQ to Sidechain (DYN SC)

This control enables the equalizer sidechain function. When the EQ sidechain is active, signal output from the EQ module is removed from the audio path and is instead routed to control ("key") the dynamics module. The EQ sidechain is enabled when the amber LED below the button is illuminated.

Sidechaining is typically used for de-essing and similar frequency-conscious techniques. To listen to the sidechain key, simply disengage DYN SC to hear the equalized signal. The sidechain dynamics/EQ implementations are true stereo when used in a stereo in/stereo out ("SISO") configuration.

Note: The EQ module must be active in conjunction with the EQ DYN SC button for the EQ sidechain to function. Note there is another dynamics sidechain available in the Filters section. (See Filters to Sidechain (DYN SC), above.)

Pre-Dynamics (PRE DYN)

During "normal" operation (PRE DYN disengaged) the audio signal is output from the dynamics module into the EQ module. Activating PRE DYN reverses this routing, so the EQ is ahead of the dynamics module instead. Pre-dynamics is active when the red LED below the button is illuminated.

4. Global I/O Meters

The vertical LED-style metering provides a visual indication of the signal levels at the input and output of the plug-in (the meters are not calibrated). The input meter is the left LED column and the output meter is the right LED column.

Note: Each meter column represents the sum of the left and right channels (it is not a stereo meter).

Input

Input controls the signal level at the input to the plug-in. The default value is 0 dB. The available range is ±20 dB. Increasing the input may result in more compression, depending on the values of the Threshold and Ratio parameters.

Note: Click the "0" to return the control knob to its center position.

Output

Output controls the signal level that is output from the plug-in. The default value is 0 dB. The available range is ±20 dB.

Note: Click the "0" to return the control knob to its center position.

Phase (Ø)

The Phase (Ø) button reverses (inverts) the polarity of the signal by 180°. The signal is inverted when the button is depressed. Leave the button out for normal polarity.

Power

The Power button determines whether the plug-in is active. Click the Power button to disable the processor. Power is useful for comparing the processed sound to that of the original signal.

An interesting article about the 4K Channel Strip can be found in the "Ask The Doctors" section of the Universal Audio April 2009 Webzine.

UAD, UAD-1, UAD-2 and UAD 4K are trademarks of Universal Audio, Inc. All other names are trademarks of Solid State Logic, which are in no way associated or affiliated with Universal Audio, Inc. These trademarks of other manufacturers are used solely to identify the products of those manufacturers whose circuits and sounds were studied during the sound development of the UAD 4K products. Use of third party trademarks are for informational purposes only and do not imply an endorsement or sponsorship of Universal Audio's products.

— Dave Crane