Exponential Audio R4 Review

Just like Nimbus and PhoenixVerb, Exponential Audio R4 has a lot of presets with the ability to search by keyword. There are 10 screens of presets to go through (over 1200) so surely you’ll find something of use 😉 You can filter by selecting a category keyword, like “Large”, “Driven” or “Guitar” and then navigate and audition the presets with the arrow keys.

To make life easier, you can enter keywords to filter the list down quite a bit. If you know you need a plate sound and something small, just click on the magnifying glass and enter “small +plate”, being sure to use the plus sign before the second word. Hit enter and the “short plate” preset will be applied, and the list is filtered down to 93 results.

16th 81 Plate Dark
Sansa dry
Sansa R4 16th 81 Plate Dark preset


Just like Nimbus, R4 has a killer filter section. The Input filter allows you to cut out frequencies on input. This can be done as a highpass, or low pass filter of 6 and 12db, or as a BandPass or NotchFilter. This is great if you want to cut some mud out of the track before sending to R4. The White line in the readout represents the Input filter. You can see below that I’m reducing at 700HZ with a -12db falloff. You can

Exponential Audio R4 Filters
Exponential Audio R4 Filters

You can similarly control the Early Reflection, represented by the blue line, and Reverb Tail, represented by the white line. Select a frequency, the type of filter to apply, and any gain reduction for that frequency. If you select band or notch, then an 4th Q knob is visible.

The Freeze button is a nice bonus. By turning it on (the big green button that says off) you “freeze” the reverb tail, and it’ll play until you turn it off. This can be used as quite a creative effect.

Vocals with Freeze applied

If a knob has been altered from it’s original setting, then there will be yellow/orange indicator under the knob. This is a really useful at a glance cue. To return to the default value, you can option-click the knob. To fine tune the value, control-drag the knob. Better yet, double click the value, and enter a number directly.

Conserve CPU

One useful, but somewhat hidden feature, is the ability to reduce the processor usage. If you click on the T in the lower right corner of the readout, you will be given a list of processing thresholds to choose from. The default is -108db. This tells R4 to stop calculating the reverb algorithm when the sound level drops below that. If it won’t be audible in the mix, then save some CPU cycles by not calculating what won’t be heard.

Center Knobs

There are 4 knobs in the center of Exponential Audio R4. The first is the Dry/Wet mix knob, followed by Pre-delay amount. If you click the Tempo button underneath, you have the option to snap to note lengths, which can be very useful keeping your reverb in time with the rhythm. Obviously this depends on your genre, as it can loose some of that natural feeling, but it can be great for dance tracks or for playing with the swing of a song. The next knob allows you to adjust the overall Reverb Time, and the final knob lets you Trim the overall level if it’s too loud.


The first tab on the right side is used to control the reverb attack. First, you can select a type, “Plate”, “Chamber”, “Hall1”, “Hall2”. Followed by the Diffusion size (surface material size) and amount for the space. A really cool readout assists you in tweaking the attack. The graphic will angle up or down along with the Envelope Attack knob, while Envelope Time stretches it out. Envelope Slope, which affects the treble falloff rate, will adjust the tops to red as more is applied.

R4 Attack
R4 Attack

Reverb Tail

The Tail tab allows you to tweak the reverb tail. Aside from adjusting the size of the space, you can tweak it by frequency. The Xover Frequency knob lets you divide the low and mids, and the Damp Frequency knob lets you divide the mid and high frequencies. You can then use the Damping Factor and Low-Mid Balance knobs to adjust the level of each. There’s a slider to control the Tail Width, from Narrow to Wide. You can also compress the reverb tail with the Tail Suppress knob, and there’s a gain reduction meter to show you how much reduction is taking place.


The Early tab lets you tweak the early reflection. There’s a graphic similar to the Attack screen, showing you the distribution of early to late reflection and you can spread the timing out. You can choose a pattern from the Early Pattern knob, which includes the previous R2 setting and a Vintage setting.


The Warp tab will only work if Warp is set to on, underneath the center Trim knob. Warp can be used to emulate analog gear. You can set a signal threshold and then apply compression, with the standard attack and release settings. There’s an overdrive type selector, along with the amount and a crossover frequency selector. It’s an effect best heard.

drums – no effect
drums with R4 Warp


The Chorus tab has some nice detuning effects. There’s a slider for chorus oscillators with options for “Pitch”, “Pitch (Fat)”, “Rand” and “Rand (Fat)”. These offer movement in the reverb tail. You can control the speed with the Chorus Rate knob and the strength with the Chorus Depth knob.

no effect
chorus effect


The Gate tab offers traditional gating effects. You set the threshold of the gate, so anything below the threshold will not sound. The amount of time the gate is held open is set using the Gate Hold knob, and the Gate Cut lets you set the gain reduction when the gate is closed. There are 2 LEDS, the Threshold is lit when the input is above the threshold level, and the Gate brightness is adjusted along with the amount effected. There’s also Gate Clamp and Gate Recovery knobs to control how long it takes for the Gate to close and reopen.

R4 Gate

Check out how sick the effect can be on drums!

drums – no effect
drums with R4’s Gated Verb effect

Final Thoughts

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Exponential Audio R4 is their flagship reverb product. They bill it as a “color” adding reverb, and claim that their entry level PhoenixVerb is a clean reverb, along with the more advanced Nimbus. The input filters are really useful in that you can scoop out the lower end that usually gets muddy with lots of build up. Freeze can be a very useful effect on vocals, as well as pads. (Or actually in place of pads, the reverb tail becomes the pad.) If you tend to have mixes that are lacking space or ambiance, R4 can definitely fill in the space for you. Also, if you don’t have a solution for gated verb, this could fill that role for you as well.

If you are thinking of buying, consider the Exponential Audio Stereo Reverb Bundle. That’s the bundle we purchased, and we’re glad we did.

Don’t forget to check out our reviews of Nimbus, PhoenixVerb, and The Best Reverb Plugin.

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Exponential Audio R4
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