UAD 4K Buss Compressor Manual
UAD 4K Buss Compressor: Tips and Tricks for Pro-Level Mixing
11 Jan 2024
The ultimate “glue” for your mix bus, re-modelled with stunning accuracy.
UAD's 4K Buss Compressor is the Plug-in version of SSL 4000 G Bus Compressor, designed for UAD-2 hardware and Apollo interfaces.
UAD SSL 4000 G Bus Compressor Plug-In Collection Trailer
The all-new UAD SSL 4000 G Bus Compressor Collection for UAD-2 hardware and Apollo interfaces is an exacting end-to-end circuit emulation that goes far beyond UA’s original standard-defining SSL G Bus Compressor plug-in
UAD 4K Bus Compressor Guide
G Bus Compressor Controls
Most SSL G Bus Compressor and SSL G Bus Compressor Legacy controls are identical.
Any control differences between the two plug-ins are noted.
THRESHOLD
The threshold defines the signal level at which the onset of the 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, the Output level is typically reduced. The Make-Up control can be used to modify the output to compensate if desired.
Note that the Ratio control interacts with the compression threshold to maintain the perceived loudness of the signal. As the Ratio is decreased, the effective threshold is lowered.
Tip: In the SSL Bus Compressor, click the “0” text label to return Threshold to its center position.
MAKE-UP
Make-up (Post-Compression make-up gain) controls the signal level that is output from the plug-in. The range is 0 dB to +15 dB.
Generally speaking, the Make-Up control is adjusted after the desired amount of compression is achieved with the Threshold and Ratio controls. Make-Up does not affect the amount of compression.
Tip: In SSL Bus Compressor, click the “0” text label to return Make-Up to its unity position.
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 ms, 0.3 ms, 1 ms, 3 ms, 10 ms, and 30 ms.
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 the Release time is set 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 s, and Auto.
The Auto-release characteristic for SSL G Bus Compressor has a unique quality that is optimized for program material.
RATIO
The 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.
Note: The Ratio control interacts with the compression threshold so the perceived loudness of the signal is maintained. As the Ratio is decreased, the effective threshold is lowered.
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 VU-style Gain Reduction 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.
The Headroom control also affects the amount of gain reduction.
SC FILTER
The sidechain filter allows the removal of low-frequency content from the control sidechain, reducing excessive gain reduction and/or “pumping” on bass-heavy audio signals without reducing the bass content of the audio signal itself.
Note: The Sidechain Filter only acts on the sidechain signal. While it can produce an audible change in dynamics behaviour, it does not act directly on the signal that is output from the plug-in.
At the lowest setting of the SC Filter control, the filter is defeated and does not affect compressor behaviour.
As the SC Filter knob is turned clockwise, the filter is engaged and its frequency sweeps between 20-500 Hz, allowing for a wide range of relationships between bass level and gain reduction.
Tip: Click the OFF text label to turn off the sidechain filter. Click OFF again to return the filter to its previous setting.
Note: Sidechain Filter is not available on SSL G Bus Compressor Legacy or 4K Bus Compressor
HR
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 SSL G Bus Compressor.
Headroom enables best practice operating level matching, or it can be used creatively to expand the sonic range of the processor.
By fine-tuning the 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.
Headroom simply changes the internal operating level so that the plug-in is not “pushed” into a gain reduction as much.
Headroom can be set (in dB) to 4, 8, 12, 16, 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 “HR-dB” text label to return the control to the default value. At higher dB values (clockwise rotation), signals push the plug-in into gain reduction (and more non-linearity and “good” harmonic distortion colour) more easily.
Set the control to a lower value (counter-clockwise rotation) when less gain reduction and less colour are desired.
Note: To avoid the temporary gain increases that can result when adjusting the 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!
Note: Headroom is not available on SSL G Bus Compressor Legacy or 4K Bus Compressor.
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 0, only the unprocessed source signal is output. When set to 100 (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 (parallel compression).
The balance is continuously variable throughout the control range.
Tip: Click the 50 text label to quickly set the control to the 50% position. Click the 0 text label to set the control to the minimum position. Click the 100 text label to set the control to the maximum position.
Note: Mix is not available on SSL G Bus Compressor Legacy or 4K Bus Compressor.
AUTO FADE
As found on the console and favourite SSL outboard units, the Auto Fade function is useful when the end of a song needs a gradual decrease in volume.
The speed of the fade can be tuned from 1 to 60 seconds and incorporates SSL’s signature fade curves.
The SSL G Bus Compressor and Legacy plug-ins provide an Auto Fade function that, upon activation, automatically reduces the plug-in output to a minimum within a specified
time. This function enables extremely smooth-sounding fade-outs (and fade-ins). As a plus, it can be automated as well.
The Auto Fade function processes the signal at the output of the compressor. The fade signal level that is output has an exponential curve.
Note: Auto-Fade is not available in the 4K Bus Compressor.
RATE
The Rate control determines the amount of time that passes between the Auto Fade button being activated and the plug-in output level being reduced to a minimum (or being raised to 0 dB in the case of a fade-in).
The available range is from 1 second to 60 seconds.
Fade times immediately reflect the current Rate value. Therefore a fade-out that has already been initiated can be accelerated by changing the Rate during the fade-out.
Conversely, a fade-in can be accelerated by changing the Rate during the fade-in.
AUTO FADE Button
Activating the Auto Fade button initiates a fade-out. The fade-out time is determined by the Rate parameter.
The Auto Fade button flashes when a fade-out is in progress and is continuously lit when the fade-out is complete (when the Rate time has elapsed).
Deactivating Fade (clicking the solid-lit button) initiates a fade-in. During a fade-in, the signal level is increased from the current level of attenuation to 0 dB of attenuation.
The Auto Fade button flashes when a fade-in is in progress, and is no longer illuminated when the fade-in is complete (when the Rate time has elapsed).
Toggling the Auto Fade button causes an already active fade to reverse direction, without a jump in output level. The Rate is constant even if an active fade is interrupted.
For example, if the Rate value is 30 seconds and a fade-out is initiated, then Auto Fade is clicked again after 20 seconds, it will take 20 seconds to fade back in.
Tip: Shift+click the Fade button to instantly return the level back to 0 dB (this feature cannot be automated).
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