Most of you know that I’m not content to simply call myself an audio geek and leave it at that. Oh, no. Someone of my advanced geekiness needs a specialty, too, and that specialty is vocals. Recording and mixing vocals is my passion.

A singer with whom I’ve been working closely was curious as to what I’d done to make her voice sound so wonderful recently. Once I had finished palpitating over that great compliment, I realized it was the digital effects unit I’d been using. The venue lacked one, so I’d brought my own as a demonstration of how useful and necessary such an item is.

I offered simply that I’d added some “reverb” to her voice, expecting that to be a satisfactory non-technical answer. To my surprise, she inquired as to what kind of reverb I’d added. Stuck for a non-technical answer to that, I replied that it was plate reverb. This drew a very comical, confused expression, and I realized I’d blundered into a situation where either a dismissal of the subject or a convoluted, boring explanation represented the only exit. I chose the latter.

Having recently gone through all of this for her benefit, I thought it might be an interesting subject with which to bore my loyal blog audience as well. So, here is everything you never wanted to know about reverb.

Reverb and echo are both, in their natural forms, the result of sound waves being reflected by objects. Echo is pretty easy to understand. You yell, “HELLO” in a big, empty canyon, and a second or two later, the shout comes back to you, having bounced off the far canyon wall. There may be more than one canyon wall that can reflect that shout, so you may hear more than one repeat of what you shouted.

As a thought experiment, let’s now create a canyon that’s full of walls, dozens of them, all placed at odd angles and random distances. Shouting into a canyon like that would produce a bewildering array of echoes, all merged together. It would be completely impossible to distinguish one echo from any of the others. The sum of all those overlapping reflections is called reverb.

Originally all reverb was natural. Almost all indoor acoustic environments have surfaces that reflect sound. Gymnasiums, bathrooms, indoor swimming pool enclosures, and concert halls all have natural reverb of widely differing character. If you’ve noticed the hollow, ringing sound of these places, or if you’ve noticed how great you sound when you sing in the shower, you’ve experienced reverb in all its natural glory.

Through the years, singers have always known that a big room made their voices sound better, bigger, and more powerful. Until the late 19th century, little was known about the reason for this effect, though, and as a result, the design of concert halls and music venues was largely hit-and-miss. Sometimes a room would sound absolutely beautiful. Other rooms would have, to put it simply, too much of a good thing.

Reverb is generally quantified in terms of its “reverb time” or “RT₆₀.” Put simply, the reverb time is the amount of time required for the reverb to die away to inaudibility (generally considered to be 60 deciBels below the original sound’s amplitude) after the original sound has ended. Rooms with shorter reverb times are wonderful for speech, but don’t enhance the sound of music. Longer reverb times will garble speech into unintelligibility, but will make music sparkle. Even longer reverb times will turn everything into a muddy, ugly mess.

When sound strikes an object, one of three things can happen to the energy of the sound wave. It can be reflected, which is what happens when the sound strikes a very hard, massive surface like stone or concrete. It can be absorbed, its energy dissipated by resistances within the object’s mass. Rubber absorbs sound in this way. Finally, it can be transmitted, passing directly through the object and continuing out the other side. This is how you can hear someone shouting on the other side of a pane of glass or a thin apartment wall. Gradually, designers of music halls began to realize that a certain combination of reflective and absorptive materials resulted in a room with corresponding acoustic properties, and that this was an effective means of controlling reverberation.

It wasn’t until around the turn of the 20th century that forward-thinking architects began to design concert and lecture halls with their acoustic properties in mind. Two of the first facilties to be designed this way were Symphony Hall and Jordan Hall, both located in Boston, Massachusetts. The designer of Symphony Hall’s acoustics, a Harvard physicist named Wallace Sabine, is widely considered the father of the new science of architectural acoustics. His name was given to a unit quantifying a room’s sound-absorbing capability, the Sabin. (I have no idea why the man has been stripped of his silent “e.” Perhaps it was absorbed.)

When artists began to record popular music, it was soon discovered that it was difficult to bring sensitive, bulky recording equipment to a proper venue in order to capture the sound of a reverberative room. Engineers began to look for ways to bring the room to the studio instead. The first artificially-created reverbs were called “chambers.” These were actual empty rooms fitted with extremely reflective walls and surfaces. A loudspeaker excited the room with the source sound, and one or more microphones picked up the resulting reverb. These chambers worked well to a degree, but suffered from two huge disadvantages. Reverb time (generally a function of the size of the room) was difficult to change, and the chambers occupied considerable space in a building that had to be kept soundproof and unoccupied.

Guitarists love reverb. When the electric guitar appeared on the music scene, amplifier manufacturers were looking for a practical way to give guitarists a reverb-like effect, and by the late 1930s, the answer had appeared in the form of spring reverb.

In a spring reverb, a transducer converts the original sound into motion at one end of a set of long, thin coil springs that are held in tension. As it passes through the springs, the energy induced gradually changes from its original longitudinal mode into a combination of transverse and torsional modes, spreading and dispersing as the energy couples from spring to spring and coil to coil. The resulting vibration, picked up by a transducer at the other end of the springs, sounds metallic and noisy, but it’s definitely reverb of a sort. By the end of the 1950s, spring reverb was extremely common in guitar amplifiers, and many guitar amps of today still employ it. Spring reverb is highly sensitive to mechanical shock, as anyone who has ever accidentally (or intentionally) kicked a live guitar amp will readily tell you.

In recording, and particularly for vocals, spring reverb remained largely useless. Although large, “studio-quality” spring reverb units were marketed and found places in studios around the world, their downfall was that they sounded like spring reverbs, not like rooms. The search continued for an alternative.

In 1957, a German company called EMT hit on a revolutionary idea. In a soundproof cabinet, they suspended a thin, flat plate of steel about four feet high and eight feet long. Amplifying the original sound, they sent it to a powerful electromagnetic transducer mounted next to the plate. The sound was thus transmitted to the plate and caused it to vibrate. The waves so created traveled outward and reflected at various times from the edges of the plate, contining to bounce around and interact with each other. Two further transducers (not unlike electric guitar pickups) retrieved this sound from the plate at different points, creating a wide stereo field. Best of all, the reverb time could be adjusted using a soft damping pad which pressed against one side of the plate; a motor-driven mechanism allowed the engineer to regulate the pressure of this pad without leaving the mixing console. The effect was absolutely breathtaking, and the EMT plate reverb was an immediate and unprecedented success. If you hear vocal reverb on a record made in the 1960s and 1970s, it’s a pretty safe bet that you’re hearing a plate.

Plates, as wonderful as they are, still have problems. As electromechanical devices, they’re still sensitive to electromagnetic, acoustic, and mechanical noise. They’re big, heavy, expensive, and largely non-portable. EMT understood this, and in the late seventies they began experimenting with digital electronics in order to produce reverberation through other than mechanical means. The EMT 250 was the world’s first digital reverb and, not surprisingly, it was designed to emulate a plate.

Everyone knew, though, that digital technology had potential as much more than a one-trick pony. In 1978, a fledgling company called Lexicon, with the help of a true renaissance man named David Griesinger, introduced the first truly practical, versatile digital reverb unit, the Lexicon 224. Despite its high cost ($8,000) and its complexity, the invention swept the industry. Soon, there wasn’t a high-end recording studio in the country that didn’t possess a 224 of one of its brethren (224X, 224XL, 200, 480, 480L.)

Digital or not, the sound of a plate reverb was still highly desirable due to its beautifying effect on vocals. So, despite all the other nice effects (rooms, halls, springs, chambers) that digital reverb units could emulate, most engineers tended to gravitate toward one plate-type program or another. As things often happen in our language, the word “plate” remained in our lexicon long after the actual physical plate had all but passed into history. Few people outside the recording industry have ever heard of a plate reverb. I suppose it’s natural, then, that I ended up describing to the lady with the great voice why program 5 on my digital reverb (made, incidentally, by Lexicon) is named “KSJ RICH PLATE F.”

What I could not explain, or at least chose not to explain in the interest of tact, is that reverb works its magic on the human voice not by enhancing it, but by hiding its imperfections. The difference between a good singer and a truly great singer, condensed down to the very basics, is the degree of control the singer can exercise over both power and pitch (amplitude and frequency to an engineer.) Because reverb tends to stretch a sound out in the time domain, we cover up small, short-duration instabilities in both the frequency and energy domains in the same way that soft focus covers imperfections in a photograph–by strategically reducing detail. Oh, of course the reverberation alone has a certain aesthetic appeal, but in general terms, the worse you are as a singer, the more a well-applied reverb will improve your sound! It would have been somewhat difficult to explain this without giving the impression that I was impugning the lady’s talent–which, in fact, I was not–so I strategically eliminated that detail from my explanation.

That’s my reflection on the subject of reflections. Next time: a treatise on the construction of soundproof showers for the dangerously untalented.