iamReverb Audio iamReverb

IamReverb say that convolution reverbs share an inherent flaw — which only their novel IR recording technique can overcome.

When a plug‑in developer adopts the name iamReverb Audio, it suggests they are pretty serious about reverb. No surprise, then, that the Vienna‑based company’s first product is an eponymous plug‑in dedicated to providing, you guessed it, reverberation; and what’s more, they claim a significant technical breakthrough.

Getting Convolved

About two decades ago, convolution was heralded as the technology that would revolutionise mixing, if only we could find computers fast enough to do it. Today, it’s a process that laptops can do in their sleep, and impulse responses are everywhere from amp simulators to virtual tape machines. But in terms of our use of reverb, it’s not obvious that it has revolutionised mixing. The same increases in computer power that have made real‑time convolution trivial to perform have also enabled algorithmic reverbs to overcome many of their previous limitations, whilst the limitations of basic convolution were soon exposed.

One obvious limitation of a basic convolution plug‑in is that it’s hard to edit or alter the sound. A well‑recorded impulse response captured in a nice‑sounding space allows the character of that space to be faithfully added to any source, but engineers who have grown up with algorithmic reverbs missed the ability to vary the duration, tone, width and other qualities of the reverberation. Another limitation is that simple convolution is a static process that cannot capture time‑variant qualities of the reverberation. The modulation options provided in algorithmic reverbs might not replicate these perfectly, but they are usually good enough, and are easy to adjust.

I’ve reviewed several plug‑ins that aim to overcome these limitations, including Liquidsonics’ excellent Reverberate, HOFA’s highly versatile IQ‑Reverb, Acustica’s novel Silver and Inspired Acoustics’ epic Inspirata. All of them, in their own way, make convolution more flexible, better sounding and ultimately more useful. But, according to iamReverb, a core problem with existing convolution techniques has remained unsolved until now.

Early Doors

In a convolution reverb, the incoming audio signal is ‘convolved’ with a short audio file known as an impulse response. As the name suggests, this impulse response is a recording of the way in which an acoustic space (or, indeed, any other system) reacts when an impulse is fed into it. But what is an impulse? In theory, it’s a burst of sound with zero duration, or at least, with a duration less than a single sample. However, no real‑world sound behaves like this, so the would‑be convolution reverb maker has a choice. He or she can use something that is a fairly good approximation of an impulse, such as a balloon bursting or a shot from a starter pistol; alternatively, a sine sweep can be played back over a PA system, and the impulse response derived mathematically from the resulting recording.

The iamReverb team have developed a new technique for capturing impulse responses which, they say, allows early reflections to be faithfully represented for the first time.Photo: Bernhard Raab

Both techniques suffer from the limitation that iamReverb have identified, but it’s perhaps more easily understood in relation to the first. Even though a gunshot is a very brief burst of sound, it’s not a perfect impulse, and thus does not die away instantly. Consequently, if the mics capturing the impulse response are positioned in such a way that the first reflection paths are only marginally longer than the direct path, it becomes impossible to fully disentangle those first reflections from the direct sound. In other words, there is an inherent limit to the accuracy with which conventional convolution techniques can reproduce early reflections. Yet, as the makers of algorithmic reverbs figured out decades ago, those first reflections provide vital aural cues about the space we’re in.

The key innovation that iamReverb claim is a new technique for capturing impulse responses that faithfully represents early reflections even when the mics are placed very close to the source.

The key innovation that iamReverb claim, then, is a new technique for capturing impulse responses that avoids this problem and faithfully represents early reflections even when the mics are placed very close to the source. As this is a proprietary technique, details are secret, but they have at least given it a snappy name: Enhanced Reverb Modelling, or ERM. The company say that ERM makes it possible to recreate the effect of hearing a nearby source in a reverberant space with a realism that wasn’t previously possible.

Three Steps To Heaven

The iamReverb plug‑in is available for macOS and Windows in all major native formats, and is authorised using the iLok system. The 300MB‑ish library of impulse responses seems to be installed separately for each format, and is invisible to the user; you can’t import or record your own IRs.

The plug‑in interface is cheerful and refreshingly bright. To my eyes, it draws on the same design language as the Teenage Engineering OP‑1 and some Baby Audio plug‑ins, which is no bad thing. And, like those Baby Audio plug‑ins, it presents a compact and very manageable set of parameters. There are just two editing pages, one for actual reverb parameters and one for setting up a simple but effective four‑band EQ.

What’s perhaps most striking about the main editing page is that most of the controls on offer are parameters I associate with algorithmic rather than convolution reverb. For example, you can freely vary both the decay time and the size of the space. There’s also variable pre‑delay, whilst the central part of the window contains three dials labelled Close, Mid and Far. On a Lexicon‑style reverb, you’d expect these to let you balance the level of early reflections against that of the tail. They do something similar here, setting the relative levels of three different, complementary IR captures made at different distances from the source.

The impulse recording process used a Dutch & Dutch 8C loudspeaker, captured using a variety of microphones and recorded through a Forssell SMP‑2 preamp.Photo: Bernhard Raab

A preset within iamReverb is thus much more than a static representation of a position within a space, which is what you usually get with an impulse response. Instead, it’s a starting point that you can fine‑tune in much the same way as is possible in a typical algorithmic plug‑in. The factory library includes over 100 presets, of which perhaps half are named after a type of space (Small Church, Long Chamber, and so on), and the other half after their suggested application (Acoustic Guitar Hall, Drum Chamber, and the like). All are derived from real acoustic spaces, and in fact the entire library is based on different captures of around 30 rooms. However, there are no plates, springs or vintage digital units, which means you can’t get the full gamut of useful reverb treatments from iamReverb. It’s also strictly a stereo‑only plug‑in, with no surround options.

Impulse Purchase?

From a technical point of view, iamReverb’s criticism of existing convolution reverbs makes sense. However, I can’t say that I’ve previously noticed anything audibly amiss with the early reflections in other plug‑ins, so I was interested to discover whether this one would provide some sort of epiphany.

Since no two convolution plug‑ins sample the same spaces from the same positions with the same equipment, there’s no useful sense in which you can do an A/B comparison between them. Consequently, I can’t be certain whether iamReverb’s good qualities are down to ERM, or whether they’re simply the result of skilful IR capture and plug‑in design in other respects. But what I can tell you is that this is a very fine reverb plug‑in indeed. Having now used iamReverb pretty much exclusively on a number of mixes, two things stand out above all.

The first is a liveliness to the reverberation that I’ve not encountered in other plug‑ins. It’s not that the sound is brighter, or that it’s compressed; more that it simply feels more present and immediate, even for large spaces. I don’t know whether this is a consequence of having early reflections more accurately represented, and it’s a subtle rather than a night‑and‑day difference, but it’s something that I consistently noticed across the entire library. There are no controls for adding or adjusting modulation to the sound, but I never felt they were necessary.

The second is that this is a reverb plug‑in made by people who actually use reverb plug‑ins, and use them for mixing music. The philosophy here is demanding in terms of quality, but not precious in terms of allowing the sound to be manipulated. For example, during the review period, iamReverb issued an update that added a switch to reverse the panning of the Far component. This is hardly ‘realistic’ in the purist sense, but it’s useful and effective in situations where you don’t want the reverb tail to be lost behind the dry sound in the stereo field.

The plug‑in’s second page is a simple four‑band EQ.

As I’ve already mentioned, that library contains around 100 presets, which might not sound all that much. But there’s an unusually high hit rate here, and none of them fall into the “interesting, but”, or the “useful for post‑production” categories. There are no parking garages, shipping containers or kitchen cupboards. Everything that’s included here has an obvious and valuable real‑world application, especially if the music you’re mixing is based around real instruments rather than synthesized sounds.

Better still, every preset has a wide and useful range of variation. The Decay and Size parameters permit quite broad changes without making things sound artificial or unnatural, and the concept of balancing Close, Mid and Far mic positions is simple and highly effective. I was initially wondering why there’s no preset category for ambiences, given the emphasis on early reflections capture, but in fact there is no real need for one. You can create excellent ambiences from a number of the existing presets, simply by reducing the decay time or by emphasising the Close position. If it wasn’t for the realism of the sound and the fact that turning the Decay and Size controls briefly mutes the output, you’d think you were using an algorithmic reverb.

iamReverb is a most impressive debut product. It sounds great, the user interface is faultless, and above all, it’s extremely usable.

In short, iamReverb is a most impressive debut product. It sounds great, the user interface is faultless, and above all, it’s extremely usable. I just hope iamReverb Audio haven’t boxed themselves into a corner with their choice of company name, because I’m keen to hear what they can do in other fields!