Review – Exponential Audio R4

Exponential Audio R4 Review Title Image

Exponential Audio offer three fantastic sounding reverb plug-ins. Phoenixverb, R2, and Nimbus. R4 ups the ante with unprecedented features to shape the early reflections and tail portions of the reverb signal independently. It is the culmination of “clean” and “character” reverbs rolled into one easy to use reverb plug-in that does everything you need and didn’t know you needed from reverb. Let’s take a look at what makes R4 unique.

Filter Modulation

To start with, you can filter the incoming audio before it hits the reverb engine. This feature alone is valuable, in that it eliminates the need for a pre-EQ plug-in on your reverb return channel strip. There are two more filtering sections in R4. One for the early reflections and one for the reverb tail. One of the new flagship features is the ability to modulate the early reflections and reverb tail filter frequencies with two separate LFOs, so they are constantly moving. This feature works particularly nicely with the band-pass and notch filter modes, as it creates a sweeping filter effect on the reverb that adds interesting and colorful movement to your reverbs frequency range.

Exponential Audio R4 Review 01 Filter modulation

Separate ER Delay and Tail Delay

One of R4’s main strengths is the ability to shape and control the early reflections and reverb tail sections independently. The onset of the entire reverb signal, beginning with the early reflections can be delayed via pre-delay that is optionally synced to the host tempo. This allows for an impressive rhythmic pulsing reverb that is tied to musical subdivisions of your song’s tempo. Additionally, the onset of the reverb tail can be offset separately from the early reflections. Using separate offsets, tied to musical subdivisions or otherwise, adds interesting complexity to the relationship between the source audio and the listener’s perspective.

Exponential Audio R4 Review 02 Predelay and attack delay

Early Reflections

Another nice addition is the ability to control the width in the stereo spectrum separately for the early reflections and the reverb tail; again adding complexity to the perceived size of the space being simulated. This feature is particularly useful, combined with the other early reflections features when mocking up orchestral instruments and establishing a position within the room for various instruments before they reach a common reverb tail.

For example, set up separate instances of the R4 as inserts on each instrument’s channel strip. Turn off the reverb tail in all of them, so that only the early reflections are audible. Adjust the early reflections attack, pattern, time, width, and slope parameters uniquely for each, to establish their positions within in the room.

Exponential Audio R4 has some new interesting and complex early reflections patterns to choose from that makes this very effective. Then set up a send on each channel strip going to a shared instance of R4 with it’s early reflections level turned off completely. Use this reverb for a shared common space, while the individual early reflections situate them each differently within that space. I don’t know of any other reverb plug-in that does this so effectively.

Exponential Audio R4 Review 03 Early reflections

Chorus and Density

R4 inherits the R2’s interesting chorusing and pitch modulation of the reverb tail. New in R4 is the addition of the Hall 2 reverb algorithm. With this comes the ability to also modulate the density of the reverb. This feature can be used either separately or in conjunction with the chorus modulation.

Combined with the chorus functions, a creamy and thick reverb tail can be established either with or without pitch modulation, depending on which chorus algorithm is used. So, in other words, the density and chorus modulation can be blended either for a subtle thickening effect, or to stand out with pitched modulation as wild or tame as desired. Or the two can be used independently.

Exponential Audio R4 Review 04 Chorus and density

Tail Suppression

One of my favorite features in Exponential Audio R4 is the tail suppression and recovery function. It acts as a kind of reverb “ducker”. The suppression knob causes the reverb level to be lowered when the input signal is strong. The recovery knob controls the “bloom” of the reverb once the suppression ends. It’s kind of like sidechain compressing the source and the reverb together so that the reverb is heard less when there is source signal, and more when there is empty space. It’s a beautiful way to control your reverb and works not only on vocals but instruments as well. At extreme settings, it’s a great “pumping” style effect. The reverb tail itself can optionally be used, either alone or in conjunction with the input signal, to trigger the suppression.

Exponential Audio R4 Review 05 Tail suppression


R4 also inherits the warp features introduced last year with Nimbus. This can dramatically color the reverb tail in a combination of three ways. First, it can be compressed. With full control over attack, release, and knee, the compression stage can vary from subtle to making your reverb very thick and present.

The second is via the overdrive/saturation stage. This is one of my favorite Exponential Audio reverb functions. I have not seen anything like this in any other reverb plug-in. Subtle “good” distortion can be added for great effect. The crossover is used to apply this distortion to a limited part of the frequency range. By restricting it and letting the highs pass through unaffected, there is a rich, thick density added to the meat of the reverb, while still retaining the bright top end. By limiting or eliminating the highs from passing through, an impressive dark quality is imbued to the entire signal that sounds fantastic.

And lastly, the Warp engine can be used to reduce the word size of the reverb. This option is useful in emulating vintage or retro style hardware based reverb sounds.

Exponential Audio R4 Review 06 Warp Engine

Gate and Freeze

The Gate functions are slightly enhanced from those found in R2. It allows the reverb levels to be controlled by the characteristics of the input signal. The reverb tail is truncated, either sharply or gradually, based on the absence of the source audio. Unlike the suppression function which reduces the level of the reverb this gates it completely (or in part). It’s perfect for getting big gated Phil Collins-style reverb effects on snare drums.

The freeze section, completely new to Exponential Audio reverbs, does the exact opposite. It allows the reverb to sustain indefinitely, regardless of whether there is a source signal present or not. This is an incredible effect and works best with larger spaces. Early reflections can optionally be blocked or allowed to pass through. When the early reflections are allowed to pass through, it creates a sustained frozen reverb sound that contains subtle movement within. Depending on the context it is used in, the freeze function may benefit from being coupled with some automation. This allows you to selectively enable/disable it at specific places in your arrangement.

Exponential Audio R4 Review 07 Freeze

Final Thoughts

The only thing even remotely related to this within Logic Pro X is PlatinumVerb; which is like an ancient ancestor compared to the functions and control available in R4. I remember when convolution reverb was all the rage, when Space Designer first came out in Logic, circa 2003. Algorithmic reverbs took a temporary back seat, but they are back and have been back for quite a while.

A lot of users find Space Designer, and similar convolution reverbs, difficult to control. They can easily overpower a sound. And draw more attention to the space than to the actual source audio. I think that was the initial appeal of convolution reverbs when they were introduced. But many engineers have come back to preferring the subtlety and less obtrusive nature of algorithmic reverbs.

We have seen offerings from UVI, Fab Filter, Waves, Zynaptiq, Eventide, and others. And they are all great. Algorithmic reverbs have a different way of blending with the source audio in a mix than convolution reverbs. Many engineers find them to be more transparent, subtle, and flattering to the source audio they are used on. Exponential Audio though seems to be in a class of their own. Their rich, fully featured reverb plug-ins offer the user the control to get everything from clean and subtle reverbs that wrap around your audio like a fur coat, to more pronounced effects that draw attention to highlighting the source audio they are fed with.

Exponential Audio R4 is, in my opinion, the culmination of all the Exponential Audio smarts that are spread through their other three plug-ins. It does just about everything they do combined, plus more. For those weary of learning to control all the the nuanced parameters available, no worries, R4 ships with over 1200 presets that will get you 95% of the way towards your final sound. Adjust the simple basic controls in the center of the interface, and you’re done. Great world-class reverb, with minimal fussing.

Exponential Audio R4 Review 08 Basic Controls

If you own other Exponential Audio reverbs, R4 is a worthy addition. In my opinion, the freeze function, tail suppression, separate width controls for early reflections and tail sections, and advanced modulation functions, are worth the price. If you are new to the brand, R4 would be my first choice of the four. It does everything the others do, and more. Exponential Audio reverbs feel like driving a fully decked out Cadillac. If you are into reverbs, you owe it to yourself to check them out.


R4 is available for $299/€289, with special upgrade pricing for existing Exponential Audio customers. The introductory period runs through March 24, the discount is $150. You can also download a free fully-functional 21-day demo of R4. You’ll need an iLok2 or iLok3. For more information, visit R4 at the Exponential Audio website.

Free Exponential Audio R4 Video Tutorial

For Groove3 subscribers, I have an hour of video tutorials showing every glorious aspect of this fantastic reverb plug-in in full detail. It’s available completely free to anyone signed up with a Groove3 account. You can find them here:

Exponential Audio R4 Explained

Eli Krantzberg
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Eli Krantzberg

Apple Certified Pro Eli Krantzberg is an internationally known author and music software trainer for Groove3. His instructional videos have helped demystify music software such as Logic Pro, Pro Tools, Sonar, BFD, Melodyne, and Kontakt for thousands of users all over the world. Based in Montreal, Canada, Eli is involved in all aspects of audio production. In his studio he works with various artists, as well as on commercial jingles, corporate videos, and original music composition.
Eli Krantzberg
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