August 06, 2013, by Daniel Keller
Along with EQ, reverb is probably the most commonly-used effect in audio. It would be nearly impossible to find a recording that doesn’t employ some type of reverb.
And probably because it’s so ubiquitous, reverb is also one of the most misunderstood and misused effects there is. It’s interesting to consider that, as with so many things in modern life, we’ve spent countless hours inventing technologies that enable us to recreate something that occurs naturally in the real world.
It Starts With The Room
In the earliest recordings, reverb was limited to what occurred naturally in the actual recording environment. The acoustical fingerprint of the space itself was an intrinsic part of the recording, usually captured by one – or at best, a handful – of microphones.
Rooms with the best sonic characteristics (typically symphony halls, theaters, etc.) were prized as the most desirable recording spaces, and this worked well for the music of the day, which was mainly in the orchestral and operatic genres.
As the Big Band era dawned in the late 1940s and early 1950s, radio began to play an increasingly major role in the way audiences would consume recorded music. The advent of audio tape recording, along with refinements in microphone technology, enabled engineers to begin to experiment with mic placement, bringing with it an expanded ability to experiment with room acoustics.
One of the first documented uses of natural (ambient) reverb to intentionally enhance a recording was by engineer Robert Fine, who introduced ambient mics on some of the early “Living Presence” recordings on Mercury Records.
The Room Next Door
The late Bill Putnam, Sr., founder of Universal Audio, was an early pioneer in employing artificial reverb in recording. As early as 1947, Putnam converted a bathroom in his studio to create one of the first purpose-built echo chambers, placing a speaker in one corner and a microphone in another, and mixing the sound with a live recording.
The unique sound of the echo chamber on Putnam’s first release on his Universal Records label, “Peg o’ My Heart” by The Harmonicats, was an instant hit, and the sound of echo chambers went on to dominate the recordings of the 1950s. Putnam would design echo chambers for his studios in Chicago and Los Angeles as well, beginning a trend of studios creating purpose-built natural reverb chambers.
Today, the few of those spaces that still exist (including the still-active chambers under the parking lot of the Capitol Records building in L.A.) are prized today for their natural sound.
The Virtual Room
As revolutionary a concept as Putnam’s echo chamber was, it still required the natural ambience of a real space to work its magic. It wasn’t until 1957 that the German company Elektro-Mess-Technik (EMT) unveiled the first plate reverb. The EMT 140 (and subsequent units, including their best known EMT 250) worked by attaching a small transducer to the center of a large, thin plate of sheet metal; vibrations from the speaker activated the surface of the plate, and were picked up by one or more small pickups attached to the plate’s other end.
The result was a dense, warm sound that emulated a room’s natural echo, yet could be dampened to vary the sound somewhat. And while the EMT plate reverbs were large and unwieldy, they still represented a smaller, cheaper, and more versatile alternative to building a dedicated echo chamber.
Another variation introduced during the 1950s, spring reverb substituted a set of springs for the metal plate. Though not nearly as dense and lush a sound, the springs required much less space, making them popular in applications where plate reverbs were impractical, including early guitar amps (Fender’s being the most well-known) and Hammond organs.
It was the advent of digital technology in the 1980s that changed the face of audio overall, including reverb. Digital reverbs made it possible to emulate the natural ambience of any space, as well as the sound of plate, spring and other electronic reverb sources. Soon, an abundance of digital reverb and multi-effects boxes began to appear in studio racks.
Some of the most popular units included Lexicon 224 and 480, and Yamaha Rev7 and SPX90. These units even made it possible to modify individual parameters to create effects that don’t occur in nature, including artificially altering early reflections (the first reflected sound), pre-delay (the time before the first reflected sound is heard), and even reverse and gated reverb (probably one of the most abused drum effects of the 1980s).
Too Much Of A Good Thing
As live recording began to take a back seat to multitracking and layering of parts, a room’s acoustical characteristics became less important – in fact, in some cases acoustics began to be viewed as something of a liability.
Studio design began to emphasize acoustically “dead” spaces, and recording techniques began to favor placing mics close to each instrument to capture as much direct sound as possible, with minimal reflections from the room. A chamber or plate reverb was then used to create an artificial “room” ambience. (Why yes, this does sound a bit backward, doesn’t it?)
These days, as digital audio workstation technology has evolved, and signal processing power has become cheap and plentiful, even the most basic, entry-level programs offer a multitude of reverbs and DSP, allowing us to easily plug in several different rooms, halls and chambers on any given track.
The challenge now is no longer which reverb to use, but what combination of reverbs will work together to create a cohesive and natural sound.
Not surprisingly, the availability of technology has made it all too easy to overdo it. Excessive or poorly applied reverb is one of the most common mistakes heard in amateur recordings. An instrument’s direct sound is critical in establishing definition and directionality – add too much reverb and your mix can quickly devolve into a lush soup of mush. Generally speaking, it’s best to approach reverb with a “less is more” philosophy; unless you’re after a cavernous special effect, try and make it almost imperceptible within your mix.
Breaking It Down
At first blush, the many parameters of a reverb unit or plug-in can appear pretty complex. Let’s try and simplify it by breaking it down to its basic physics.
Like throwing a stone into a pool of water, sound emanates from the source in waves. Those waves eventually hit multiple surfaces (walls, ceiling, floor, seating, whatever) and echo back, mixing with the original sound. The way we perceive that sound is dependent on a number of different factors, including how far away those various reflective surfaces are, what they’re made of, where our ears are located in relation to the original and reflected sound waves, and a host of other, more subtle factors like temperature, humidity, altitude and more. In most cases, what we hear is the product of thousands of echoes, reflected many times.
Our brains decode this information in a number of different ways:
—The first echoes that occur when sound waves hit surfaces (early reflections) and the amount of time between the initial sound and those first reflections (pre-delay) work together to tell us how large the space is, and our position within that space.
—The length of time until the echoes die away (decay) also helps determine the size of the space, but the way that decay interacts with the early reflections also makes a difference. For example, a small but reflective room (e.g., a tiled bathroom) can have a decay time similar to a larger hall, but the smaller room’s early reflections will arrive sooner.
—The tonal color of the reflections also plays a critical role. The reverb in that tiled bathroom will be considerably brighter sounding than a larger room with wood or fabric-covered walls. Larger halls will also attenuate different frequency ranges at different rates, and the combination of which frequencies last longer also affects our perception of the space.
—Other factors also affect our perception, including density (how tightly packed the individual reflections are) and diffusion (the rate at which the reflections increase in density following the original sound). A large room with parallel walls will usually have a lower diffusion rate than a similarly sized room with non-parallel or irregularly shaped walls.
As you can imagine, creating a natural sounding ambience is a complex, multi-faceted process that involves programming dozens of interdependent parameters.
Generally speaking, unless you have a degree in advanced acoustics, it’s best to find a reverb program that comes close to what you’re looking for, and keep the tweaking to a minimum.
What Do I Use With…..?
Among the most frequently-asked questions of first-year recording students is the question of what types of reverb work best with a specific instrument.
The first rule of thumb is always “trust your ears” – if it sounds right, it probably is.
Beyond that, here are a few general guidelines:
First and foremost, as stated earlier, less is almost always more. You’ll achieve a more natural sounding mix using fewer reverbs sparingly than you will by booting up every plug-in in your arsenal. One short, bright program (small room or plate) and a larger, warmer program (large room or hall) will often be enough to cover most of your mix.
For best results, insert reverbs into an effect or aux buss, rather than directly into a signal chain. This will enable you to use the same reverb for multiple tracks, while varying the amount of send for each source.
Drums and other percussive sounds typically sound more realistic with small to mid-sized rooms (shorter reverb tails, shorter pre-delay), or plate programs. Avoid longer pre-delay times, which can create the impression of a “phantom” doubled attack, as well as longer decay times, which can adversely affect directionality and clarity.
Too bright a reverb can result in a harsh, brittle sound, particularly on snares and cymbals. Lower density settings can also sound coarse and unnatural on drums. Higher densities and warmer reverbs will generally deliver better results.
Acoustic instruments like strings, woodwinds and backing vocals can typically benefit from larger room and hall settings and longer pre-delay times, which can help to smooth, blend, and add depth to these parts. Background vocals in particular can often benefit from a larger room setting, which can help to smooth and blend multiple parts.
These larger settings can also do wonders for widening a stereo field. Conversely, too much of this effect can blur and instrument’s attack and create a “swimmy” sounding mix with little definition or directionality. Unless you’re after a very lush, ethereal background, be careful not to overdo it.
Lead vocals are another story entirely. The general rule of thumb is that there are no rules; the song and the production dictate what’s right. That said, most producers will agree that short, relatively dry settings work best for rock, while longer, more dense reverbs are best saved for lush ballads. Using a longer pre-delay before the actual reverb kicks in allows the vocal’s clarity and impact to cut through, but gives it a natural “tail” that rings out without blurring.
One trick for helping to define, rather than blur, the imaging in your mix, is to use reverb in combination with delay. Pan the original sound slightly to one side. Delay the reverb return slightly (try anywhere from 3 to 10 ms) and pan it to the opposite side. This works particularly well to help separate sounds in similar frequency ranges, like multiple stacked guitar tracks.
Don’t Be Afraid To Experiment
I’ve spent most of this column talking about using reverb in its most natural settings. And for the most part, the best use of reverb is a mix in which it’s pretty much indiscernible – the more easily you can hear it, the less natural it sounds.
But as I tend to say in most of my columns, don’t be afraid to break the rules. Experimentation is how most of the best ideas are born. Try combining a couple of different instances of the same reverb with slightly different parameters and panning them left and right. Or try adding a subtle chorus or distortion to a reverb.
One engineer I worked with frequently used to route the mix through a pair of Vox AC30 guitar amps, mic those in a small, bright room, and blend a tiny bit of it back into the final mix. The result was an ever-so-subtle bit of grunge that worked great for the rock bands I often brought to his studio.
Again, subtlety is key here – a little bit of something unusual, buried deeply in the mix, might be just the thing to give your mix that special “something.”
Daniel Keller, a.k.a., the Studio Curmudgeon, is a musician, engineer and producer. Since 2002 he has been president and CEO of Get It In Writing, a public relations and marketing firm focused on audio and multimedia professionals and their toys.. Despite being immersed in professional audio his entire adult life, he still refuses to grow up.