Intelligent EQ Plugins Comparison: soothe2, smart:EQ 3, Smooth Operator


I’ve always been on the lookout for synths and effects that redefine how we create music or that redefine music itself. The last couple of years have given us some innovative plugins, and quite a few dynamic EQs have appeared.

Here, I’m taking a closer look at three newly released “intelligent” equalizer plugins: soothe2 by oeksound, Smooth Operator by BABY Audio, and Sonible’s new smart:EQ 3 plugin.

Three different products, all aiming to facilitate mixing decisions, with an aptitude for taming sibilance and removing muddiness. What a beautiful time to be reviewing VST plugins!

Note that this is not a shootout: all three products have their strengths, but slightly different foci. Still, the article ends with recommendations for use cases and purchasing recommendations, so read on if auto EQ might be something for you in this “balanced” overview.

Introducing Intelligent Dynamic EQs

In a world where everything from our phones or homes to the buildings we (usually) work in carries the “smart” label – hey, even my toilet paper is labeled “smart” – one may wonder where the hyperboles end and actual value begins.

Maybe one should draw the line at dynamic EQs. “Smart” or not, they are great helpers on one’s way to a great mix.

These EQs are all dynamic, meaning they constantly analyze and then adapt to the incoming audio using EQ and compression in combination, which is nicely indicated by their user interfaces.

It is, however, up to the user to change the suggested settings provided by presets or, in the case of smart:EQ 3, a machine learning-assisted EQ curve for a given audio source.

The constant adaptation to incoming audio differentiates these EQs from static EQs, which are simply filtering the audio source through several static EQ nodes.

As their names imply, Smooth Operator and soothe2 have similar aims: to make the listening experience nicer. They (especially soothe2) do this by removing sibilance, clearing up muddy or overall resonant parts of the frequency spectrum, and taming general harshness.

smart:EQ 3 has more of a general approach toward mixing, though it too can be used to deal with, say, problematic sibilants. smart:EQ 3 also features a novel feature for carving out space from less needed tracks, which I consider quite a big thing.

Read on to get a sense of what each one of the three plugins does. Thoughts on sound comparisons follow after the presentations.

soothe2: Integrity Preserved

soothe2 by oeksound.

soothe2 by oeksound.

Of the three equalizers featured here, soothe2 is the one that puts the user in control to the largest degree. The flexibility can seem a bit daunting, and it needs some time getting used to, especially being a tool made for pretty surgical operations.

On some material – vocals particularly – soothe2 impresses with its sonic correction capabilities, and not surprisingly, it is marketed as a “dynamic resonance suppressor.”

Somehow, the developers have managed to keep harshness away but keep the rest of the sound intact. It’s hard to explain as that is a bit of a contradictory statement, but the only way I can describe the effect is that the signal’s integrity is preserved.

Technically, I would assume this is a matter of precision, but it must also have to do with a deep understanding of the musical aspects of sonic integrity.

The developers have provided the user with several goodies, including a quality setting. As audio quality significantly affects processor use, the ability to set the quality to low during production and high during rendering is helpful.

“Real-time” and “offline” settings mean that during playback, it’s possible to run soothe2 with very low processor use, and when the track is bounced or the final mix is rendered, full quality will be used.

The quality setting is a feature I’d love to see more often: imagine running tens of instances of complex synth patches without worrying about the strength of your hardware or how long your PC battery will last.

Another thing I like about soothe2 is its user interface. As mentioned, the UI is a bit complex, but it is well thought out, and it looks great.

The preset menu is perfectly arranged, so dialing in a suitable preset is done in seconds. However, I have a nitpick here.

When a new preset is selected but the menu still is open, the EQ nodes are updated. This is good. But, the preset menu obscures the main window, so it’s not possible to get a quick glance at the preset. A solution is to select the first preset of a particular category – say, electric guitar – and then use the arrow keys of the interface to watch preset settings for this preset category.

A nice detail is that the exact frequency for the cursor is shown when moving the cursor throughout the main pane. This is a good feature. However, I’d like the same for the dB axis, to quickly show the user the attenuation or current volume for the frequency at the tip of the pointer.

Overall, I’d say oeksound has done some exemplary work on attention to detail, from the included tutorial to the tooltips and the included delta feature (only hear what’s being altered).

In summary, soothe2 oozes professionalism.

Compared to Smooth Operator, soothe2 brings a more extensive assortment of core features, such as more EQ shapes, stereo features, and several controls for calibrating sensitivity. This means soothe2 has a different target audience in mind.

Smooth Operator: Impressive achievement

Smooth Operator by Baby Audio.

Smooth Operator by Baby Audio.

Smooth Operator may be the simplest of the three products, but the spectral analysis capabilities and its beautifully thought-out user interface indicate the quality that lies beneath the GUI.

Referring to Smooth Operator as an “intelligent signal balancer,” as BABY Audio does, seems fair.

BABY Audio has spoiled us with several diverse effects over the last two years, including Super VHS, the competent multi-effect Spaced Out, and now Smooth Operator. Working on such a range of effect paradigms within a relatively short timeframe is quite an impressive feat.

In my opinion, Smooth Operator surpasses the developer’s earlier efforts, and I can’t help but wonder what this talented company will surprise us with next.

Interestingly, its UI is turned upside-down compared with soothe2: the lower the setting, the more reduction. Both ways make sense, but keep it in mind if you demo both products or when you look at side-by-side comparison screenshots.

One thing I like about Smooth Operator is that it is very pleasing to the eyes (though some more contrast between the background color and active parts would sometimes make it easier to view).

Just looking at the EQ and the attenuation is quite a soothing experience in itself.

Also, in my view, the absence of advanced controls works in Smooth Operator’s favor: it’s easy to dial in a good sound. However, I miss soothe2’s convenient delta listening feature, that is, the ability to hear what the plugin removes or adds.

A bit oddly, there is no dB scale. Thus, I cannot see precisely how much Smooth Operator attenuates the signal.

I can imagine BABY Audio made a design decision to omit a dB grid for aesthetic and clarity reasons. However, in an update, perhaps showing a dB grid could be a togglable feature.

Another issue is the (lack of) order of the presets. I’d much prefer a submenu system with vocals, guitars, etc., than a pseudo-random set ordered by producers who’ve come up with the settings.

A more serious point is the non-weighted output of the plugin. I’d like the plugin to compensate gain automatically to avoid the “louder is better” effect.

Finally, more EQ nodes could be useful. Then again, it’s a tradeoff.

I sort of like Smooth Operator’s cockiness – aiming to deliver a great sound with a minimum of options. Still, when going back and forth between the two plugins, I sometimes miss the advanced screen of soothe2 and can’t help but wonder why the developers keep hiding the controls from the user (as was also the case in Spaced Out).

If you’re up for sonic experimentation, Smooth Operator is simply a joy to use: drag points about and try different settings on the fly.

Automating these changes works well and makes sense as I feel this is a rather creative and sound-sculpting plugin. And so, I can imagine Smooth Operator can get creative uses in, say, EDM or ambient genres.

Overall, this is a lovely product that I’d be happy to use in either a hobby or pro-environment.

smart:EQ 3: Mixing redefined

smart:EQ 3 by Sonible.

smart:EQ 3 by Sonible.

Like soothe2 and Smooth Operator, smart:EQ 3 can help make the entire mix clearer by cleaning up muddy parts and removing harshness as such instances appear.

It must also be said that the auto-learn feature is very smooth. Fire it up, select a profile, hit play and its record button, and the profile is ready.

Note that there is currently a lack of instrument/vocals profiles. From what I understand, they need to be adjusted for the third version, so more profiles will be added with an update.

The EQ curve in smart:EQ 3 is set like this: first, the user chooses a template “profile” and plays back a portion of the track (say a few seconds of lead vocals).

As smart:EQ 3 “knows” what a female lead vocal EQ curve typically looks, it adjusts the incoming audio to match it. In normal mode, then that’s about it: the curve is used throughout the song, with a minimum of CPU power needed.

However, as with the other two plugins, the magic happens when smart:EQ 3 is put in “dynamic mode.” Now, it responds to the audio input dynamically. For one thing, this means smart:EQ 3 can handle sibilance issues.

But the cool thing about smart:EQ 3 is yet to come, so read on!

Inter-track mixing with smart:EQ 3

For several years, I have envisioned an EQ that truly works beside the composer.

It would be a tool that allows one to define the priorities of voices/instruments in a mix and then treat them dynamically so that the vocals “carve out” the frequency space from the synth pad.

As it happens, smart:EQ 3 does precisely this, as a world-first for a multi-channel environment. Both Smooth Operator and soothe2 (as well as WavesFactory TrackSpacer and a few other products) can work for side-chaining, but not like this, where all channels are engaged.

This new feature works surprisingly simply: tracks with the EQ switched on are grouped together as per the user’s wishes. Each group (up to six in total) is then assigned to one of three priority levels, as seen in the screenshot below. When the play button is hit, the smart:EQ instances adapt to the incoming audio and compensate for tracks that have precedence over specific frequencies.

In theory, the result should be a mix with added clarity, where muddiness and harshness are but memories.

Moreover, the mix should be perceived as louder even though the master levels may not have changed. The reason why is that supporting tracks can be played back louder, as only a region of their frequencies needs attenuating.

So, if you’d like your mixes to be cleaner, well-balanced, and perceivably louder, then smart:EQ 3 may well be your new secret weapon.

In truth, I am excited about the possibilities of this plugin, and for me, it could well turn out to be the plugin of the year. However, I feel it needs more mileage before I can truly make up my mind about it, and in any case, more sonic profiles are necessary to make it justice.

When simply replacing my earlier EQs with this concept, I feel that whereas soothe2 often works quite subtly, smart:EQ 3 sometimes does too much to the signal.

That said, I realize that, like iZotope’s master assistants, the plugin only provides a rough sketch. It is up to the user to mold the EQ curve into finished work. When smart:EQ 3 seems too aggressive, bringing down the “Strength” attribute is advisable.

It is noteworthy that Sonible also develops a “smart” reverb and a compressor. It feels only logical that they will make it possible to run those tools together, to simultaneously control both EQ, compression, and reverb, similar to what iZotope does today with Neutron, Ozone, Nectar, and the acquired Exponential Audio reverb technology.

Then again, I suspect it is only a matter of time before iZotope catches up with inter-channel EQ, and it would be interesting to compare the two competitors when and if all of this happens.

Dynamic EQs: The Comparison

The “AI” segment is the most important for EQs designed to improve the source audio somewhat automatically (or “automagically”).

My overall finding is this: all three tested plugins are exceptional at what they do. However, given their dynamic nature, it is often hard to predict which plugin will deliver the most appealing result. It is also impossible to make accurate A/B comparisons because of this feature.

In my opinion, soothe2 is the most “transparent” of the plugins. It does its thing but doesn’t color the sound.

Smooth Operator delivers a pleasing sound, but it does have more character, primarily when used with high settings.

smart:EQ 3 is so complex that it depends on the use case and other parts of the mix (remember to bring up its dynamic setting so that it notices changes to the incoming sound).

Note that the actual sonic differences are slight. I bet that in a blind A/B comparison test, most wouldn’t be able to notice when the plugins are changed for one another (after some curve matching).

So with that, again, I argue all three do a good job, especially after some tweaking. Remember that these plugins are virtual mixing assistants, not mixing engineers.

For my experiments, I developed a tool where I phase-inversed one of the effects’ audio to be able to listen to and visualize its audio compensation. I tried this both against a dry signal and against the other two plugins.

I found that when I had dialed in somewhat similar settings, the nuances weren’t substantial between the tools’ modifications, and in many cases, they were barely audible or visible.

I tried the three plugins on vocals, strummed electric and acoustic guitars, and entire mixes. I also checked them on over-sibilant vocals, on which I tried to replace my current de-esser with the plugins’ de-esser settings.

These are my findings.

Vocals Test

When applying to vocals, soothe2 took out annoying frequencies but somehow kept the rest of the vocals intact. I would like to refer to this as “vocal integrity preserved.”

smart:EQ changed the overall EQ curve, but for the better, and I was pretty happy with the results (to further tweak so that the vocals were aligned with the somewhat pierce-through quality I was after).

Smooth Operator also changed the sound in a pleasing way.

Guitar Test

On the guitars, all three plugins picked up more or less the same frequencies.

With Smooth Operator and smart:EQ 3, it was easy to dial in a more pleasing sound than what was recorded. I noted that one of the guitars was a bit too percussive.

Of the three plugins, soothe2 did the best job in bringing down the percussiveness.

De-essing Test

As a de-esser, none of the plugins could fully tame a difficult vocal passage I chose. In that particular passage, the sibilants differed in frequency and intensity due to a variety of “ess,” “sh,” and “ch” sounds.

As the EQs are dynamic, I assumed they would handle all of these issues with ease. However, that didn’t turn out to be the case.

The problem went away soon enough with a bit of automation, so this wasn’t a big downer. I felt that the plugins gave comparable results, and I would be happy with either choice for this situation.

I can only conclude that all three plugins deliver, but none works without user intervention.

Dynamic EQs: The Conclusion

This begs the question: why pay for soothe2 when you can apparently get by with Smooth Operator for a third of the price?

To me, part of the answer lies in soothe2’s advanced controls. I feel that when a ballpark setting is achieved, soothe2 allows for some critical fine-tuning.

Another part of the answer is its transparency. Once again, the differences are pretty subtle, and all may not agree with me on this, but I did find soothe2 to leave the intended sound intact to a higher degree than the others.

Another reason is soothe2’s mid/side processing feature for work on stereo sources. As soothe2 is meant for slight variations, I like the delta feature to hear how it tries to improve the signal.


As mentioned in the introduction, there is no winner or loser here. All three plugins have strengths and weaknesses, and the sonic differences are often tiny.

Instead, here are my recommendations for a few suggested use cases.

For a hobby musician on a budget, you can’t go wrong with Smooth Operator. Plus, the learning curve is less steep than what you can expect from soothe2.

In fact, the name “smooth operator” is quite descriptive.

For a small or large studio, soothe2 would be a great addition. Put it first on effects chains of vocals, electric guitars, and acoustic guitars and have some of your critical EQ mixing decisions made in no time.

My suggestion is also to get a copy of Smooth Operator as a backup. After all, you may prefer its pleasant sound on some sources, and they perform differently in different cases.

For anyone who wants to take advantage of multitrack mixing, there is simply no alternative to smart:EQ 3, and the tool does it at a great price.

However, smart:EQ 3 is not meant to substitute the other two plugins but to open new possibilities.

So, I’d suggest demoing at least two plugins and seeing which one works for you.

In the context of this overview, it must be said that a fourth option is not to buy any of these plugins. After all, they are designed to facilitate the mixing process, and it is, of course, technically possible to achieve comparable results by hand.

Also, doing things entirely by hand leaves the user in complete control.

So, while I assume many studios would place soothe2 first in the effects chains of vocals and guitars to save time, there will always be the option to fight sibilance and spectral imbalance manually.

When comparing the tools, I’d like to label them this way:

  • soothe2 – the problem solver;
  • Smooth Operator – the beautifier;
  • smart:EQ 3 – the next-gen approach to mixing.

Still, any of them can be used to deal with problem-solving and to increase the clarity of the mix, so choosing your plugin is a matter of taste, money, mixing experience, and available time.

I can’t wait to work more with smart:EQ 3 on a mix, from start to finish and for different genres. I believe this is the future of mixing, even though it is still a bit early to see whether Sonible has succeeded.

We will need more instrument profiles and, why not, genre-specific mastering profiles (the latest versions of Ozone and Tonal Balance Control come to mind).

I will also try Smooth Operator on more sources, as it’s easy to dial in pleasing results. soothe2 will be reserved for when it’s truly needed, a fine tool as it is.

Final Thoughts

Making this comparison has been a rewarding and also revealing journey.

The big surprise for me has been the quality of Smooth Operator. Sonible’s and oeksound’s products are well recognized, and the two looked into here both expand on their developers’ earlier success stories.

I didn’t expect that a new product with a somewhat limited feature set and an appetizing price would be able to compete.

Whatever you decide, remember who’s in charge – you and not these tools!

Featured products: soothe2 / Smooth Operator / smart:EQ 3

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About Author

Growing up with electronic music in the 80s, Petter Terenius later graduated in musicology, art history, and IT. Having worked in the music tech industry, he is now at Lancaster University, UK.


  1. Markus Schlösser


    Thanks, good comparison!
    IMHO gulfoss also belongs to the category, did you ever compare it /check it out?

    • Petter Terenius



      First off, thanks!

      Although Gullfoss works on individual tracks, it primarily shines on full mixes or buses, so we didn’t include it here. (It’s also older than these tools’ updates.) An interesting alternative to Gullfoss is Zynaptic’s Intensity, so if you’re especially looking for full-mix-“exciters” (which I’d say they technically aren’t), I suggest you try the demos of those plugins. They’re both highly recognised. TBH, I don’t think you could go wrong with Gullfoss. Intensity would (in my opinion) be more of a personal choice (your music will sound more clear but just maybe a bit cold).

  2. On internet fora a lot of comparisons are made between Oeksound’s Soothe and TBPro’s DSEQ3, sometimes in favour of the first, sometimes the latter. However, in pro reviews it seems that DSEQ3 isn’t mentioned that much when talking about “intelligent” equalizer plugins, alltough Soothe is 200$, when DSEQ3 is only 80$. It would be interesting to see them compared by someone from the pro-community.

  3. Great comparison, thank you.

    Noticed though that it should say Izotope acquired Exponential Audio, because newfangled audio was acquired by eventide.

  4. TBProAudio DSEQ should’ve been there instead of smart:EQ. With all due respect, this is a different kind of a tool that was designed for a different task.
    Also there are Voxengo TEOTE, Soundtheory Gullfoss and sonible Balancer, a yet another different kind of automatic dynamic EQs, aimed at balancing the spectre of the signal in broader strokes.

      • Also worth considering if you do an update – Mastering The Mix’s “Reso”, reasonably priced akin to Smooth Operator, unlike Soothe2, which is out reach for, I would guess, a large majority of the reader-base of BPB, at least for those who pay for what they use.

        Even more relevant for BPB – a free Max 4 Live device designed specifically to emulate Soothe2 called Boba. The dev actually does a tonne of “emulations” of much more expensive, well-known plugins to surprisingly decent effect. Some standouts are –
        Cambridge Bloatinizer (Oxford Inflator)
        Spectacle (Wavesfactory Spectre)
        Jacked Brat (Sausage Fattener)
        Lo-Fi (You guessed it)

        Along with straight up useful devices. And doesn’t charge a penny (all donationware/pay-what-you-want).

  5. yuzaintheclouds


    i saw a lot of mentions of dseq, but i’d say that voxengo’s teote is also a good alternative. super underrated.
    would be nice to see your opinion on both of them in comparison with the rest of them.

  6. Melda’s MSpectralDynamics might be the first one that came with this concept. It does the same thing as Soothe and is even more flexible. It is an equal contender and should be featured in such a comparison as this.

  7. Hello! A question if I may – looking at these for Black Friday. I already have Smooth Operator, so from this excellent comparison, I won’t look at the other two – think SO fits my needs and skills perfectly. However, Gullfoss – would it be beneficial to have this too in your opinion? I have downloaded it, and I can notice a real difference when placed on bus or master, but it would be great to get an expert opinion. FYI – I am at the intermediate level now with Ableton (2 years in). Cheers!! (and love the site!)

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