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Review: Acustica Audio’s Ruby & Azure EQ’s Sound Superb

This level of realism and analog authenticity doesn't come cheap as far as processing power is concerned.


If you're a regular reader of our reviews, you know that we're big fans of the innovative work that the team at Acustica Audio has been doing over the past several years. The company's Acqua plugin line has ignited mega-buzz in production and engineering circles, and to my ears their plugins routinely offer the most accurate recreations of analog EQ's, compressors, and effects processors in the digital realm.

Two of Acustica's recent releases—Ruby (which recreates the famed D.T. Fearn VT-4 EQ) and Azure (modeling a custom-made vacuum tube mastering EQ)—offer a substantially different take on how to recreate the magic of analog EQ in the box. In this review, we'll take a deep dive into both plugins and see where they might benefit producers and engineers looking to upgrade their EQ toolbox.

It's important to note that Ruby and Azure are purchased separately and not together on the Acustica store. For the purposes of this review, we are merely contrasting the differing EQ styles of both.

Setup & First Impressions

As of 2018, Acustica's installation and setup process is managed exclusively through the desktop Aquarius software, which acts as a centralized installation and update manager. Getting up and running with both Azure and Ruby was easy—just install the plugin formats you need via Aquarius, open your DAW, and you're good to go. Acustica's license terms are among the most generous in the industry, with 5 activations allowed per license.

Opening both Azure and Ruby side-by-side reveals two very different UI's appropriate for different mixing applications. Azure is an 8-band beast of a mastering EQ (not including it's four filters, two high pass and two low pass), whereas Ruby is simple by comparison, offering 4 bands of EQ in addition to a high cut filter. Both plugins feel snappy and responsive, especially when compared to Acustica's older releases, which often exhibited a lag between the user interface and the resulting audio.

In Use

If you've read our previous reviews of some of Acustica's outstanding plugins—like Diamond, PINK 2, or Ebony—we've gone into great detail there about what makes Acustica's Acqua plugins so unique. To briefly summarize, whereas most plugins use algorithmic means to recreate the sound of classic hardware, Acustica's proprietary sampling process uses actual impulse responses and samples of the hardware itself to recreate the authentic tone and character of the original unit. There truly is a different sound to Acustica's approach, and the difference is often far from subtle. Much in the same way as real hardware, Acustica's EQ's are usually capable of ridiculous amounts of gain adjustment without ever sounding harsh or overly pushed—something that I've seen very few algorithmic EQ plugins achieve.

If you're after a boutique, high-end EQ suitable for vocals, synths, as well as busses and stems, you really can't go wrong with Ruby, which is an officially endorsed digital recreation of the famed D.T. Fearn VT-4 Vacuum Tube Stereo Equalizer. While the VT-4 is hardly the most common hardware EQ you'll find in major studios, it's easily one of the most desired, with a sound that's legendary for its smoothness, openness, and general 'expensive' character.



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Ruby is a 5-band EQ offering Low Cut, Low Boost, Mid Cut, High Boost, and High Cut controls with fixed frequency selections and unstepped gain controls. As a result, it's not the most flexible EQ you'll ever encounter—this isn't the tool to use if you need to make a precise cut on a nasty resonance or if you need gain at a very specific frequency—but it excels at making beautiful, broad cuts and boosts capable of radically reshaping the tonal character of a sound without ever sounding harsh or unnatural. While digital EQ's have come a long way in the past few years, I still often find them to have a fundamentally different sound than high-end analog EQ's; many digital EQ's, especially those built in to most DAW's, often sound like they're adding something unnatural to a sound when operating at high gain settings, especially at 8kHz and up. Really great analog EQ's, by contrast, more so feel like opening up a low pass filter on a sound rather than adding something that isn't already there; it's the difference between uncovering frequency content that's inherently part of a sound rather than adding something that's not.

As is typical for Acustica EQ's, Ruby excels at this, and it particularly shines on vocals and drums; it's capable of completely opening up the top end of a vocal with natural air or adding natural but defined and room-shaking bass to a kick or synth bass lead. As a result of its Vacuum Tube design, Ruby (and the original VT-4) is not a transparent unit. This is the type of EQ that adds a bit of character to a signal merely by touching it, and part of the magic of Ruby is its ability to beef up the low end of a drum stem in a fundamentally different way than a sterile digital EQ would. While Ruby is at home on just about any channel or buss in a mix, it can also make a phenomenal master buss EQ, provided you're after fairly broad adjustments. Ruby has no Q control (with the exception of the high band), so this is really a broad sculpting tool rather than one for precise boosts or cuts.

Whereas Ruby is a phenomenal mix EQ, Azure would likely be overkill to run on individual channels—although if your computer can handle it, there's certainly no reason not to, as it sounds incredible on just about anything. Azure is an 8-band mastering EQ featuring Left/Right and Mid/Side configurations, and either setup can operate in linked or unlinked mode. Both channels also feature a switchable high and low pass filter with 3 stepped frequency controls for the broad shaping of the low and high end.

In contrast to Ruby, Azure features fairly flexible Q controls on all 8 bands, and it can have a vastly different sound at identical Gain and Frequency settings with different Q values, ranging from precise boosts and cuts at the .5 setting to broad tonal adjustments at shelving settings. Unlike the original hardware Azure is based on, the plugin's 8 bands operate independently and do not feature a parallel design. As a result, gain is consistent regardless of the settings of other bands, which is a marked difference from a parallel EQ setup. Azure is highly flexible and truly sounds incredible whether it's on the master buss, stem, or individual sound. It's pretty much impossible to make this unit sound harsh or bad even at extreme gain settings, and it lends a smooth, musical width and character to any sound that passes through it. Azure sounds dramatically better than my DAW's stock EQ—it really isn't comparable, to be honest—and if you're looking for an EQ that will get the absolute best out of any source sound or mix, Azure is right at the top of the list in my book.

The only downside worth noting with Acustica's Acqua processors is their CPU hit. This level of realism and analog authenticity doesn't come cheap as far as processing power is concerned, and we'd recommend you demo either plugin—especially Azure—to make sure it runs smoothly on your system. I tend to use Acustica's EQ's and compressors sparingly during the production and mix process unless I plan to render a channel to audio, saving them for separate mix and master sessions with fewer plugins and no virtual instruments. CPU hit aside, both Ruby and Azure are phenomenal tools for adding analog tone and enhancing just about any kind of source material.

We'd highly recommend both Azure and Ruby for any producer or engineer looking to tap into the sound of two magical hardware units. While each plugin has a markedly different sound and is appropriate for different mix needs, both sound absolutely phenomenal and are a giant leap up over your typical stock DAW EQ's. Highly recommended.



  • Ruby shines on drums, vocals, and busses — sounds incredible
  • Azure is a top of the line mastering EQ — flexible and sounds gorgeous
  • Both plugins offer convincing recreations of boutique analog EQ's
  • Azure and Ruby feel snappy, with much less lag than previous Acustica releases


As always, Acustica's top-shelf processing comes at a heavy CPU hit.



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