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UA 175-B & 176 Tube Compressor Collection

In this article

Get the rich tube compression that changed recording.

Often cited among the crowning achievements of audio pioneer and UA founder Bill Putnam Sr., the 175-B and 176 compressors are prized for their rich tube gain reduction character and sonic flexibility. Now you can get the same legendary sounds as the rare hardware with the only authentic plug-in emulation of the original UA 175-B and 176 compressors.

  • Add vintage compression and detail to vocals, drums, guitars, and more with one of Bill Putnam Sr.'s most coveted designs 
  • Spice up synths with harmonically rich tube amplifier and transformer saturation 
  • Creatively enhance the dynamics of your most important sources with 2:1, 4:1, 8:1 and 12:1 ratio controls
  • Get perfect drum and vocal sounds easily with Dry/Wet Mix parallel processing and Headroom controls 

Add a Legendary Limiter to your Studio

Introduced in the early 1960s — and used on thousands of seminal records — the UA 175-B and 176 were the first compressors purpose-built for studio recording and mixing music, giving engineers groundbreaking fast attack time and independently variable Attack and Release controls. 

Experience Deep Tube Sonics

Based on a pair of UA's 1960s golden units, the UA 175-B and 176 Tube Compressor Collection gives you all the ultra-musical harmonics and colorful saturation of these original units — down to their magical feedback compression circuit — giving you softer compression at lower input levels and harder, nearly brickwall limiting at higher levels. 

Get the Rich Sound of an All-Around Champ

Perfect for vocals, drums, guitars, and more, the UA 175-B and 176 plug-ins give you all the character and juice of the originals — indistinguishable from the target hardware in blind listening tests. Easily add depth to room mics or a drum bus, give your guitars definition, park a bass in a mix, and inject vocals with energy. You can even turn off the compression and use the 175-B/176 plug-ins as a "tone box," lending rich tube textures galore.

Key Benefits

  • Add vintage compression and detail to vocals, drums, guitars, and more with one of Bill Putnam Sr.'s most coveted designs 
  • Spice up synths with harmonically rich tube amplifier and transformer saturation 
  • Creatively enhance the dynamics of your most important sources with 2:1, 4:1, 8:1 and 12:1 ratio controls
  • Harness plug-in-only features like Dry/Wet Mix parallel processing and Headroom for user‑customizable operating level
  • Use with any audio interface, no UA hardware required

 


 

Operational Overview

The UA 175-B & 176 Tube Compressor Collection includes the two individual UA 175-B and UA 176 plug-ins, as shown below. Both plug-ins have their own unique features and sonic characteristics.

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UA 175-B interface

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UA 176 interface

Applications

Generally speaking, the primary use for the UA 175-B and UA 176 plug-ins are as individual inserts for sources that require compression or limiting, such as an individual snare, vocal, or guitar track, or for multi-instrument sources such as a stereo drum bus.

Because the UA 175-B and 176 Tube Compressor Collection also models the input and output amplifiers, these plug-ins can also be used as "tone boxes" to add color without compression/limiting by setting the ATTACK knob to the OFF position.

Parameters

Using these plug-ins is a study in simplicity. Input simultaneously sets the compression threshold and the level of the signal entering the plug-in, while Output sets the final signal level. Attack sets the time it takes the compressor to respond to the incoming signal, while Release sets the time it takes for the signal to return to its initial level. The VU meter displays the amount of gain reduction (GR.) or input/output levels.

Control Response & Interactions

The UA 175-B and 176 Tube Compressor Collection plug-ins are meticulous emulations of the original hardware in every regard, including control responses and interactions. Both models have unique characteristics for gain, threshold, compression knee, distortion onset, and sweet spots. Setting the controls to the same positions on the different plug-ins may yield different results, especially depending on the source signals.

This accurate control modeling also applies to the Input and Output controls and amplifier levels. The same knob positions on one could produce a louder (or softer) level on the other.

Ratios

The earlier UA 175-B has a fixed compression ratio of 12:1 (thus behaving more as a limiter), while the newer UA 176 has four available compression ratios. The graph below from the original UA 176 hardware manual illustrates how the response knee is gentler at lower compression ratios. The 175-B's sharper knee is the same as the 12:1 curve on the 176 (topmost curve in the graph), so the 175-B is commonly used when limiting behavior is desired.

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Response curve graphs from the original 176 hardware manual

Grit

A simple trick is turning the attack and release up all the way to their fastest settings. This has the audible effect of adding compression distortion to the audio source., when the attack and release are so fast that minute level fluctuations create distortion. This setting can add a very useful, gritty compression effect.

This effect is useful on bass, where you might need compression and distortion at the same time, and the 175-B/176 can provide both in a unique way. This trick also sounds great on screaming lead vocals.

Modernized Controls

Several features have been added to the plug-in models that don't exist on the original hardware.

The Headroom (H.R.) control enables adjustment of the internal operating reference level for the UA 175-B and UA 176. By increasing the Headroom (by rotating the control counter-clockwise), signals at the input can be pushed higher before they compress. 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.

A parallel Mix control lets you blend your unprocessed signal with the compressed signal, opening worlds of textural possibilities on everything from a drum bus to a mix bus. The Sidechain (S.C.) Link switch allows for independent L/R channel gain reduction or provides uniform L/R gain reduction when the plug-ins are used on stereo signals. Finally, on the 175-B, the Hi/Low gain switch is moved from an internal jumper to the front panel.

Artist Presets

The UA 175-B & 176 Tube Compressor Collection includes presets voiced by prominent Universal Audio artists. Artist presets are accessed using the preset browser.

Carl Glanville

Darrell Thorp

Jacquire King

Joel Hamilton

Ross Hogarth

Dave Isaac

Devin Powers

Joe Chiccarelli

Peter Mokran

Steve Levine

Artists that have provided presets for the UA 175-B & 176 Tube Compressor Collection

 


 

UA 175-B & 176 Tube Compressor Collection Controls

Note: All controls for UA 175-B and UA 176 are identical except as noted.

Gain (175-B only)

The two-position Low / High rotary switch changes the gain level at the input to the plug-in. When set to High, the signal level is increased by approximately 10 dB. On the original hardware, this feature exists as an internal jumper. The plug-in exposes the feature on the front panel.

Tip: Click the LOW or HIGH text labels to switch to the value.

Ratio (176 only)

This four-position rotary switch sets the active compression ratio. Ratios of 2:1, 4:1, 8:1, and 12:1 are available. 12:1 is typically used when peak-style limiting is desired, while the lower ratios are typically used for general dynamic range compression.

Tip: Click any ratio text label to quickly switch to the setting.

Input

Input adjusts the attenuation of the input gain amplifier, thus controlling the amount of gain reduction as well as the relative threshold. Rotate the knob clockwise to increase the compression amount. The knob is calibrated to 2 dB values (within analog component tolerances).

Tip: Click any silkscreened gain value or "dot" surrounding the knob to jump to that value.

As with the original hardware, Input is a stepped control (by default), with each step adjusting the level by 2 dB. However, the plug-in allows the knob to be changed to a continuous control with the Vernier switch.

Output

The Output control determines the final output level of signals leaving the plug-in. Output does not affect the amount of compression. To monitor the output level, set the VU Meter to Output.

Tip: Click any labeled gain value or "dot" surrounding the knob to jump to that value.

After the desired amount of compression is achieved with the use of the Input control, Output can be used to make up for any gain lost due to gain reduction.

As with the original hardware, Output is a stepped control (by default), with each step adjusting the level by 2 dB. However, the UAD plug-in allows the knob to be changed to a continuous control with the Vernier switch.

Vernier

This two-position rotary switch changes the behavior of the main Input and Output knobs. When the switch is pointing towards the left (the default setting), the Input and Output knobs are stepped controls that operate in increments of 2 dB. When pointing towards the right, the Input and Output knobs are continuous controls.

Tip: Click the VERNIER label to quickly switch between stepped and continuous modes.

On the original 175-B and 176 hardware, the Input and Output knobs are always stepped in 2 dB increments, and the dedicated Input and Output Vernier knobs facilitate fine-level ±2 dB continuous level control between the 2 dB steps. In the plug-ins, this control has been repurposed to allow the same level of fine continuous control throughout the full Input/Output control range.

Note: When automating Input and Output in a DAW, automation lanes for these parameters always appear as continuous values, including when Vernier is set to stepped values. However, the automated values always reflect actual control values.

Attack

Attack sets the amount of time it takes for the compressor to respond to an incoming signal and begin gain reduction. Approximate attack times are continuously adjustable from 100 microseconds to 1000 microseconds (all values are extremely fast).

Note: The attack time is fastest when the Attack knob is in its fully clockwise position, and slowest when the knob is in its fully counter-clockwise position.

When a fast attack time is selected, gain reduction kicks in almost immediately and catches transient signals of very brief duration, reducing their level and thus "softening" the sound. Slower attack times allow transients (or partial transients) to pass before limiting or compression begins on the rest of the signal.

Note (UA 176 only): Actual attack time varies slightly based on the selected ratio. Higher ratios will maintain the fastest attack times.

Attack OFF

When Attack is in the OFF position, the I/O amplifiers remain active, while the compression circuit is bypassed. This feature enables the plug-ins to add color without dynamics processing.

To avoid unexpected level changes that can result when compression is disengaged, the OFF text label must be clicked to move the Attack knob to the OFF position.

Tip: Click the OFF text label to disable the compression circuit. Click OFF again to return Attack to the previous value.

Release

Release sets the amount of time it takes for the compressor to return to its initial (pre-gain reduction) level. Approximate release times are continuously adjustable from 27 milliseconds to 527 milliseconds. Actual release times may vary slightly depending on the program material.

Note: The release time is fastest when the Release knob is in its fully clockwise position, and slowest when the knob is in its fully counter-clockwise position.

If the release time is fast, compression distortion as well as "pumping" and "breathing" artifacts can occur, due to the rapid rise of background noise as the gain is restored. However, if the release time is too slow, a loud section of the program may cause gain reduction that persists through a soft section, making the soft section difficult to hear.

Tip: Generally speaking, release times should be lengthened as the low frequency content of the program material increases.

Sidechain Link (S.C. Link)

When the plug-in is used in a stereo-in configuration and the S.C. Link switch is engaged, both channels of the stereo signal are compressed in equal amounts, preventing shifting of the stereo panorama. When S.C. Link is off (down position), the amount of gain reduction is independent in each channel of the stereo signal. The sidechain link is engaged when the switch is in the UP position and the S.C. Link lamp is illuminated.

Tip: Click the S.C. Link lamp to toggle the setting (the lamp is adjacent to the switch).

Note: When the plug-in is used in a mono-in configuration, the switch is locked in the down position and its indicator lamp remains unlit.

VU Meter

This is a standard VU meter that displays the input level, the amount of gain reduction, or the output level. The mode being displayed depends upon the setting of the Meter Function switch.

Meter Select

This switch determines which mode is being displayed by the VU meter. Input, Output, or GR (gain reduction) levels can be selected.

Tip: Click a meter select switch label to quickly switch to that mode.

When Meter Select is set to GR, the VU meter indicates the amount of gain reduction level in dB. When set to Input or Output, the VU meter reflects the relative level at the input or output of the plug-in (Input/Output metering is not calibrated).

Note: When set to Input, the VU meter reflects the incoming signal before attenuation by the Input control.

Headroom (H.R.)

Headroom enables adjustment of the internal operating reference level for the plug-in so that the plug-in is not "pushed" into gain reduction as much. Headroom enables best practice operating level matching, or it can be used creatively to expand the sonic range of the processor.

Note: The Headroom control does not exist on the original hardware.

By fine-tuning headroom, the nonlinear I/O distortion and compression response characteristics can be tailored independently of signal input levels. Increasing headroom (by rotating the control counter-clockwise) allows signals at the input to be pushed higher before they compress.

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 H.R. text label to return the control to its 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.

Balance (BAL.)

This "set screw" control adjusts an amalgam of the independent plate and cathode bias current balance trims found on the original hardware. Rotating the control from its default position changes the amount of additive signal deflection ("thump") that occurs due to signal attacks.

Tip: Click the BAL. text label to return the control to its default value.

Optimally calibrated bias currents are achieved when the screw slot is at its default value. On the 175-B, the default value is -7.0. On the 176, the default value is -6.0.

Note: To avoid the DC settling artifacts that can result when adjusting Balance, automating this control is not recommended.

Mix

A blended 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.

Note: The Mix control does not exist on the original hardware.

When Mix is set to 0%, only the unprocessed (dry) source signal is output. When set to 100% (the default value), only the processed (wet) signal is output. When set to 50%, an equal blend of both the dry and wet signals is output. The balance is continuously variable, and phase accurate, throughout the control range.

Tip: 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.

Power

This toggle switch is the plug-in's bypass control. When Power is in the down position, plug-in processing is disabled, and processor usage or UAD DSP usage is reduced (unless UAD-2 DSP LoadLock is enabled).

Tip: Click the ON text label, or the power lamp (at left of switch), to toggle the Power setting.

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The original Universal Audio hardware units

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