Acoustic waves are always on the move, transmitted by air, water or solids, an ensemble of physical vibrations flowing outwards like ripples on a lake.
The brain interprets these waves as sound, which may depend on our degree of hearing loss. When sound hits a tightly packed barrier of atoms, like a wall, waves are reflected back in the opposite direction, which is called reverberation. These reflections are more sharply defined when the transmitted sound waves are shorter, for example a speaking voice. In music, the reflections (from hard surfaces) are persistent and varying in frequency, creating an ensemble of ambience. However, when recording instruments, we need to control this array of reflections to enhance frequencies, either by designing rooms to reflect sound in a certain way or by using reverb effects plugins, to achieve a desired feel.
Invention of artificial reverb
The earliest sound recordings in radio and TV, were recorded in echo chambers, a specially designed room that reflected sound, often with the addition of angled, wooden surfaces to redirect sound waves, depending on the desired effect. This is an era long before we redefined echo chambers as less welcoming social networks. In contrast, recording studios for music, were designed to be totally sound proof, eliminating reverberation entirely. This allowed engineers to mould sound very precisely, adding reverb via electronic effects units, as and when they needed it. Many popular music recordings of the late 1950s and throughout the 1960s are drenched in artificial metal plate (and later spring) reverb. The dry, pre-recorded sound feeds into the unit and is re-recorded with a microphone.
Artificial reverb units through the ages: Plate Reverb (1950s), Spring Reverb (1960s) and the more convenient (and cheaper) Reverb Pedal from the 1970s.
Room design for natural reverb
Every enclosed space you can imagine is effectively an echo chamber, from your bathroom to a cathedral, they all reflect sound, but it’s hard to control the reflections to suit a desired ambience without modifying the architecture. We can make small adjustments to our homes, perhaps designate a spare room as a makeshift, sound-proofed, music studio. We also need to control the transmission of sound in both directions, both outside street noises and the noise we make inside the room. Keeping sound contained within your studio is not just good for healthy next-door neighbour relations, but also helps to create dynamic, natural sound reflections (or reverb). There are limitations, we can’t recreate a multi-room studio for different vibes. So we enhance natural reverb with digital effects plugins.
Bathroom as guitar studio
The main advantage with artificial reverb is cheapness and the endless creative possibilities. You still need to capture sound recordings with good microphones, the room is less important because we can do lots of post-production, enhancing reverb even more. Instruments or vocals should be recorded reasonably dry, with a little air, then if we want a really wet, airy sound later, we can boost with digital reverb. There might be occasions when we want natural sound reflections. Led Zeppelin recorded John Bonham’s drum kit at the foot of a stairwell at Headley Grange. Perhaps your bathroom or airing cupboard has pleasing acoustics. Though engineers today will more than likely recreate low-fi reverb effects using digital plugins. In that sense, the process of shaping the ambience of music to your creative needs, will forever combined both physical space and artificial techniques.
Alongside recording natural reverb in physical spaces, modern digital reverb effects allows musicians to enhance and simulate any location they can imagine.
Building a church in the studio
The amount of reverb applied to a recording is measured in dryness or wetness. For example, lots of reverb wetness would produce the effect of performing in a large church. As you reduce the wetness, thus increasing the dryness, the room (or space) shrinks in size. We often think of reverb in terms of physical spaces, even when in most cases, we are using artificial reverb. It helps the creative process to imagine where your music is being performed. Sound engineers have varying tastes, some like dryer reverbs, others prefer to drench their music in reverb. I hover between the two. For me, I associate the heavy use of reverb with haunting 1960s pop music. A dryer use of reverb is more intimate and warmer, perhaps suited to solo acoustic guitar songwriters. A good technique for music made with several instruments, is to mix dry and wet, record bass and drums fairly dry, then apply lots of reverb to synth or string sounds. Employing a contrast of warmth and wetness really colours the final mix and makes the music shine.
Decay expands or shrinks room size
A key variable of reverb is the decay of reflected sound. Decay is the length of time sound reflections linger, measured in milliseconds. Decay is harder to adjust in a natural space because the furniture and fittings are usually fixed and you can’t move the walls further away! Unless of course it’s a specially designed acoustic studio, with adjustable panels. The decay of reverb becomes shorter as you add more objects (or people) to a space. It’s why an empty room is more echoey than the same room full of people, there are more surfaces for sound to absorb into or bounce off. More often, engineers will adjust the decay setting on their reverb effects unit or plugin, to simulate room size. The decay setting in a digital plugin is a very powerful tool, taking you way beyond what is possible in nature. And to such an extreme that you can simulate ethereal string sweeps or synthesised choral drone effects.
Apple’s Logic Pro has an excellent built-in reverb tool, with adjustable settings for decay in milliseconds and fine grain control over audio frequencies.
1980s reverberation revival
Without reverb, music is lifeless. Even dryer settings add a little sparkle to a mix. There was a trend in the 1970s for recording studios to strip rooms of all ambience entirely, almost sucking the air out completely. Maybe that’s why a lot of 70s rock sounds a bit smokey and dry, you can almost taste the tobacco (or cocaine). Tighter compression also added to this tense vibe, particular with drums or bass guitar. As we moved into the 1980s, artificial reverb units were cheaper, pop music sounded big again, a return to the days of the earlier (and costlier) reverb drenched recordings of the 60s. Reverb can also help to round off the sharp edges of a mix. I like a fairly dry reverb setting for bass guitar, which makes it a bit smokier. To warm up the high frequencies, I’ll apply a roomy reverb setting, with lots of decay.
Reverb plugins for post-production
There are now limitless reverb plugins available on the market. I’ve road tested quite a few and found myself sticking with a couple of good ones. Waves are a brilliant digital effects brand that came to my attention because of their Abbey Road vintage plates and echo chamber emulators. Waves are also endorsed by Beatles remixer and producer Giles Martin. FabFilter, an audio effects maker who’s products I’ve used for many years, provide an excellent, modern Pro-R reverb plugin with a vast scope of possibilities to simulate almost any physical space and beyond. There is a Black Hole preset, which ambient drone artists might find useful. There are also more creative options in Native Instrument’s spacey plugin Raum, adding crystalline or metallic sound fragments to standard reverberation.