Six Degrees of Reverberation

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In recent years, a new kind of electronic reverberation technology has emerged, known as convolution. The term refers to reverb that uses an actual recording—a digital sample—of an acoustic space that''s fed with a short burst of sound known as an impulse response. The qualities of the reaction of the space, minus the impulse response that fed it, are then mathematically convolved into the entire reverb sound.

Convolution reverbs are very realistic, but involve heavy calculations that can load down an unaided processor. Using a convolution reverb in a DAW, running natively, can be problematic because even a single instance of a convolution reverb plug-in can bog down a project enough to prevent other plug-ins from operating.

By contrast, the more traditional (non-convolution) forms of digital reverb are referred to as algorithmic because their sounds are derived from algorithms that only synthesize the properties of a reverberated signal. Algorithmic reverb doesn''t start with or use an existing sound. (For some helpful tips on differentiating the properties of convolution and algorithmic reverb, see the sidebar “Practical Differences Between Convolution and Algorithmic Reverb.”) Algorithmic reverbs have a much lower CPU load and other desirable attributes.

It''s those very “algorithmic attributes” that have inspired this plug-in roundup. Our criteria were straightforward: All of our entrants had to come in at less than $300 and had to work on the three major plug-in protocols (VST, AU, and RTAS); had to be low-impact (in terms of CPU load); and, of course, had to use algorithmic technology. Two of our prospective candidates didn''t meet all of these requirements: D16 Group''s Toraverb doesn''t run on RTAS, except through a wrapper, and VirSyn''s Reflect uses impulse responses for some of its sounds. Yet we allowed these two to participate as they fit in nicely with respect to features, price, and sound quality.

Because the six contenders are algorithmic, run natively (no hardware accelerator required), and won''t break the bank, any of the models profiled here would be an excellent choice for mobile recordists or musicians who don''t have access to a screaming machine to record. Here are six worthy offerings for adding algorithmic reverb to your recordings.

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FIG. 1: 2CAudio''s Aether has a sleek, futuristic interface and boasts a staggering number of editable parameters and innovative features.


When you launch it, Aether (see Fig. 1) presents you with a high-tech, smoothly rounded, Wii-controller-like interface that puts you right in the mood to start dialing up and tweaking 3-D sounds. The main screen is divided into three sections—Early Reflections, Late Reflections, and In/Master—and shows two images on either side of the screen: one of a photo-realistic rendering of the acoustic space you''re working in and the other of a shaded EQ curve. Not to be left out, the middle section sports an active, circular-axis L/R phase meter.

On the left side of the screen are the space controls: Size, Position, Shape, Pre-Delay, Absorb, Color, HF Soft, Cascade, and four Early Reflection parameters. The center section has the Time parameters, the right side has the EQ-related controls, and the bottom of the window shows the signal I/O controls. The separation of the regions works quite well, with so many controls and so much real estate devoted to ER parameters. The EQ section is deep and complex, but offers incredible opportunities for tone-shaping, and the graph does a good job of showing several parameters simultaneously by superimposing different colored slope lines and shaded backgrounds.

Switching tabs in Aether converts the screen into an intuitive browser. Though comprehensive, it''s straightforward and easy to use, and offers perhaps the best way to access Aether''s astonishing number of presets: Search for a sound that''s close to what you want and tweak to taste. As a bonus, six Easy Mode parameters (each lockable to preserve a setting as you audition separate programs) and the stereo meter are shown along the bottom, facilitating more meaningful browsing. Neat!

My favorite programs alternated between the classic and experimental, testifying to Aether''s strength and depth in both arenas. Stellar categories included Classics, Halls and Space Types, which I relied on for normal workday reverb tasks. But Mystical (see Web Clip 1), Thematic, and Modulation FX were inspirational and invited deep exploration with Aether''s 75 parameters. These reverbs, whether emulating a classic space or introducing an otherworldly environment, all sound organic and fully realized.

Aether is quite complex and targeted when you want it to be—it includes features such as oversampling, band-limited interpolation, spectral modulation, and a discrete early reflections engine—and will satisfy technophiles who want to tweak at the frequency-specific level. At the same time, the browser takes over the whole screen when you switch tabs, offering an intuitive way to find reverbs that are close to—or often exactly—what you want. If you like tweaking your reverb, you will love and learn a lot from Aether.

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FIG. 2: Overloud''s Breverb offers a DAW-controller-like interface with assignable and automatable faders.


Designed by veteran DSP engineer Thomas Serafini, Breverb''s interface (see Fig. 2) has a highly evolved and modern look—the most state-of-the-art in our roundup. The photo-realistic elements look much like a hardware DAW controller, with long-throw, mixing board–like faders for adjusting parameters. You can also customize your view of the interface, similar to a DAW, and the parameters and layout are extremely user-friendly and easy on the eyes.

I was pleased to see several unusual things. First, Breverb offers a full EQ section, which allows you to tailor the frequency response with great specificity—not just with damping or other high-cut controls on the tail, but full-spectrum controls over the frequencies of the entire reverberant sound. It also limits itself to just four main algorithms: Hall, Room, Plate, and Inverse. But all sounds are rich, smooth, and, in the case of the first three, ultrarealistic.

Automation at the level Breverb provides is unique and effortlessly integrated using the faders. The six faders are Read/Write-automatable, and long-throw linear-motion action vs. a rotating knob makes automation the Breverb way not only viable but irresistible. The faders offer a handy way to quickly and precisely edit parameters (grabbing knobs with a mouse can be tedious), and they allow you to automate them with a high degree of control. DAWs offer plug-in automation, but it''s sometimes limited to input and output; Breverb provides full automation of any parameter from within the plug-in interface itself.

It was inspiring to see the Inverse programs get just as much processing power as their acoustic-space counterparts, so if you have not explored this take on reverbs, Breverb will give you the best possible picture. Try them on vocals and exotic percussion instead of—or in addition to—another instance of Breverb with a normal ambient treatment. My favorite programs included Cathedral and Chamber 1, plus the Hall program called Orchestral Beef-up (see Web Clip 2), which especially shined when used with automation engaged and some judicious fader-riding. Automation has never been so much fun—or creative.

Serafini''s engineering background is evident in one key aspect: low CPU load, even with numerous multiple instances of Breverb in the same session. I opened 24 insert effects of Breverb and never got a CPU warning, and the manufacturer reports that 120 instances of Breverb ran simultaneously on a 2.4GHz MacBook Pro Core 2 Duo. While your mileage may vary, you could very well run 24 to 32 stereo returns and be safe knowing that Breverb would not throttle your system while providing stunning realism.

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FIG. 3: IK Multimedia''s Classik Studio Reverb resembles the front panel of an outboard reverb unit and provides two complementary editing modes, Easy and Advanced.


Classik Studio Reverb (CSR) looks comfortingly like the industrial-strength, black-box classics of yore, with its no-nonsense rotary knobs and red-segmented LED readouts (see Fig. 3). The interface''s design, along with the parameters it includes—and the whole vibe created by CSR—will put users of Lexicon and other iconic hardware reverb units right at home.

CSR offers four separate plug-ins—Hall, Inverse, Plate, and Room—that must be individually loaded to access the separate algorithms. Programs within each space type are then selected using a pulldown menu in the Preset window. This produces a choice of two submenus: Send or Insert. Choose one directory or the other, and you can quickly route your reverb in a single motion. Slick.

At less than $100, CSR offers a lot more than its price—or main screen—implies. Technically a single-screen interface, CSR displays different parameters depending on whether you select the Easy or Advanced mode switch. Easy mode shows higher-level functions, cherry-picked and based on the type of reverb because sometimes that''s all you need in order to marshal a preset into the desired sound. The Advanced mode provides access to all the parameters, including a powerful modulation matrix (including two LFOs and Envelope controls) that control the signal''s I/O. Another bonus? Four assignable and nameable faders for various macro functions make it possible to create morphing effects using a single control. My one wish-list item would be the ability to enter digits directly into the numerical display; currently, the only way to achieve a specific value is via knob turns.

Once selected, a program can be edited in either an A or B bank, using, say, A for your unchanged control and B for your edited version. Selecting the A and B buttons then allows quick comparisons. Each CSR module is loaded with 20 presets from which to choose, but you can save an unlimited amount of your own, easily assigning them to their appropriate Send or Insert category.

CSR would be a top choice for someone who''s used to high-quality reverb but doesn''t want to learn a complex software-based interface. I especially liked the Room reverbs (see Web Clip 3), with the Halls coming in a close second. Because of its arrangement into separate instances for the space type, CSR has a low CPU load. Classik Studio Reverb is blessedly hardware-like, both in its programming and it its high-quality, classic, and musically useful sounds.

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FIG. 4: VirSyn''s Reflect uses convolution technology for some of its programs, combining up to 200ms of an impulse response with an algorithmic tail.


Reflect is a hybrid of convolution and algorithmic technologies combined in a seamless, clever way, and keeps the price down to boot. It has a straightforward interface (see Fig. 4), but its simplicity makes it easy to learn quickly. A fixed column on the left side is dedicated to the well-organized browser. The rest of the screen shows an array of knobs that are physically grouped (and color-coded) by function. The knobs display their exact values when you mouse over them while displaying pointer marks for at-a-glance referencing when you''re not actually adjusting them.

Three yellow knobs control Size, Damp, and Stereo (room size, brightness/high-cut, and stereo image width, respectively) for the early reflections; six blue knobs control the tail. I achieved particularly nice results manipulating the Absorb, Diffuse, and Mod controls in the tail. Balancing the two Size controls between the Early Reflection and Tail portions was also fruitful and constructive. It must be said that even though the interface separates the early reflections and the tail—one is convolution-based and the other algorithmic—you hear them as one smooth, unified entity. An EQ section lies underneath, with adjustable high/low-shelving controls, and sweepable low-mid and high-mid bands.

As stated by Reflect designer Harry Gohs, the plug-in''s primary aesthetic is to emulate classic algorithmic reverbs as represented by Lexicon, Bricasti, and others. Reflect doesn''t produce the wilder effects associated with other models; rather, it focuses on realistic emulations of rooms and halls. Particularly nice were Brass Hall and Golgumbaz, which both used the convolution and algorithmic aspects to their best purposes (see Web Clip 4).

The thrust of Reflect''s power is demonstrated in its Early Reflection stage. In the program''s first incarnation, Reflect used algorithms to carefully calculate from real or artificial sources. In this version, convolution technology—using an actual impulse response—is employed for the first 200ms. A nice feature is that you can toggle between the Waveform view of the IR and the Timeline, showing the first 200ms of the early reflection. Users can load in their own IRs, too. It''s nice to hear how a real audio file can be economically integrated into an algorithmic reverb—whether that impulse response is a real room or the output of a classic hardware reverb.

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FIG. 5: Rob Papen''s RP-Verb has a straightforward interface but offers the Distortion and Envelope controls that can act on either the audio or the reverb.


Rob Papen is well-known to electronic musicians as a respected designer of software instruments. His reverb plug-in, RP-Verb, includes RP-Delay, a nice companion program for your ambient needs.

RP-Verb''s main screen looks like a classic hardware device, with a black background, brushed-chrome knobs, white lettering, and blue-background displays (see Fig. 5). The labels may be harder to read at a distance than some other reverbs, but the layout is spacious and logical. The four main sections—Ensemble, Early Reflections, Reverb, and Late Reflections—can be toggled on or off to instantly hear the contribution of a particular stage toward the overall sound. Distortion (a parameter not offered on most reverbs) is also selectable and adjustable. Beneath the main window and ringed by a chrome border are the Envelope and EQ controls. RP-Verb has an intuitive, well-laid-out setup that facilitates fast editing.

RP-Verb''s three pulldown menus for browsing seem a little redundant, but they offer a quick way to summon any preset once you learn it. As with Classik (see above), you can''t directly enter numerical values for the parameters, but mousing over a knob reveals the precise numerical value—whether in dB, milliseconds, or percent. Grabbing a knob puts a blue glow around it to let you know it''s active—another nice touch.

Including Distortion control in a reverb is a hint toward RP-Verb''s more adventurous leanings. Papen views this control as a total sound contributor—just as when you mike drums with overhead mics, strap on a compressor, and then gate the results. This approach is well-represented in the Drum Disto programs (see Web Clip 5). Also high on my favorites list were the collection of Storm Room programs. In these, the tails are dense and lush, and are—if not ultrarealistic in many cases—a great choice for fattening up instrument sounds. But don''t pull up RP-Verb for just the wacky effects with hard-sweeping envelopes. While it can do those well, RP-Verb also excels at straightforward room and hall sounds, with dense, smooth tails that are realistic, musical, and pleasing right out of the box.

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FIG. 6: D16 Group''s Toraverb offers great sounds for the price, including ones that favor more experimental efforts.


For the price, it''s hard to imagine a better reverb deal than Toraverb. True, its one screen is smallish and the labeling is hard to read, but its sounds will delight and inspire, especially if you''re looking for more creative applications (see Fig. 6). The customizable Browser does a great job of sorting its presets into Dry/Wet and Wet categories (an intuitive take on Send and Insert), and it offers up as much in the way of experimental sounds as realistic space renderings. That''s fine, as some of my favorites included the whooshy, sweeping metallic sounds found in Cristal Cave, Metal Walls, and Mutiny on Bounty (see Web Clip 6).

While Spartan, the interface has separate EQ stages for tweaking Early and Late Reflections. For the three parameters that govern Early Reflections (Size, Diffusion, and Attenuation), Toraverb provides the same-named ones, plus Feedback and Bass Cut. An appreciated touch is Late Reflection''s Size parameter''s real-time display, which reads out tenths of a second—a bonus for sound designers and video scorers who have to watch ring-out times. Controls for crossfading the Early and Late Reflections, and a Modulation control offer some useful tools for experimenting.

Its strength lies in the way it modulates the delay lines in Late Reflections, which lend an almost melodic quality to the tails. The fact that the program is easy to use and provides well-thought-out presets for conventional and original settings is a plus, as is its price.

The good news is that all six of these reverbs installed easily, worked flawlessly, and ran multiple instances without taxing my CPU. So in that respect, you can''t go wrong with any of them. Your choice will ultimately lie with the personality of the sound (and your definition of quality) and with the interface, especially if you''re going to spend a lot of time tweaking the presets, in addition to browsing through them to use as is. For those on a budget, Classik Studio Reverb would be the top choice even though it''s not the cheapest. Its ease of use and excellent classic emulations will allow traditional recordists—and those used to hearing the quality delivered by outboard hardware—to hit the ground running.

Toward the higher end, the programs diversify more into choices of personal taste. Aether will appeal to those who are technically proficient and who sculpt their reverbs as carefully as they would any other aspect of the music. RP-Verb and Reflect strike a nice balance between affordability, interface design, and great sound, with RP-Verb getting the edge because of its innovative tone-shaping controls. Breverb is the most expensive, but it features a state-of-the-art interface; unparalleled automation; smooth, classic sound; and a level of detail and warmth in its programs that make it a pleasure to use.

Yet even as convolution technology gains popularity, it''s clear that algorithmic reverbs are alive and well. And that''s a lesson we can all take note of.

Some Practical Differences

Convolution and algorithmic reverbs use mathematical operations to achieve realistic reverb results; they just approach the job in different ways using different tools. Rather than study the higher math involved to differentiate between the two processes, it may be helpful to consider a familiar analogy: samplers vs. synthesizers.

The sampling process begins with a digital recording of, say, an actual instrument. Sampling does a great job of capturing the key aspects of the sound—the transient (the initial sputter of a trumpet or bow-scrape of a violin), plus the first milliseconds of the sound, where so much of the information resides that helps listeners distinguish, say, a clarinet from a flute. In a synthesizer, everything from the transient to the pitch-bearing waveform is artificial—synthesized with white noise, wave generators, and envelope controls. This is similar to how algorithmic reverb works and has worked for the entire history of electronic reverb hardware.

Convolution reverbs are excellent for deriving real-world acoustic environments (just as samplers emulate acoustic instruments), yet they''re harder to twist into bizarre-sounding and otherworldly effects than their algorithmic counterparts (similar to the way synths can create alien lightsaber bursts with very little effort as compared to a sampler). If you''re seeking pristine and realistic reverbs, and money and powerful, tricked-out computers are no object, convolution is the way to go. If you like vintage machines, playing with knobs to get unexpected and creative sounds, and if you''re concerned about preserving CPU horsepower, or if you just like the traditional way of deriving recording studio reverb the way it''s always been done (through black-box magic), algorithmic reverbs offer tremendous options.

Jon Chappell is the author of The Recording Guitarist: A Guide for Home and Studio (Hal Leonard), Digital Home Recording (Backbeat Books), and Build Your Own PC Recording Studio (McGraw-Hill), and has written six books in the For Dummies series (Wiley Publishing).