REVERBERATIONS PART ONE
ROB LONG APOLOGISES FOR THE DELAY IN GETTING THIS STORY TO YOU…
This will be a two-part article: part one discusses the fundamentals of different reverb types, while part two will serve as an in-depth workshop on usage.
After EQ and compression, reverb is probably the most used effect in recordings. Like all processing applications, though, there are many variables, and producing a great result requires a good understanding of the possibilities, and discretion in choosing the most appropriate type of reverb for the application.
Reaching for a generic reverb as a ‘talent enhancer’ to placate a vocalist is quite often the first thing that happens after the artist hears their vocals back through the monitors. It’s often a reaction to hearing themselves raw and recorded cleanly, without the usual bounce and rumble that they're used to hearing through PA speakers at gigs or in rehearsals. Volume, reflections and the blending of audio signals generally mask imperfections, and often give an ‘enhanced’ impression of the actual performance.
In defence of the confronted performer, it’s important to realise that this is traditionally how live music is heard, both by the musicians and their audience – in a live space which has inherent reflective properties and reverberation characteristics. Thus, the dry, clinical sound of the raw studio track – unenhanced and naked – is unnatural and confusing to the ear, and makes many people feel insecure about their abilities.
But of course, reverb is not just about replicating natural spaces, making people feel comfortable or masking issues. It’s also used as a creative tool to create atmosphere, give a larger-than-life sound to a recorded part, lengthen note decay times, distinguish one sound from another, and to combine sound sources like sonic glue.
Let’s look at the most common types of reverb. Reverbs can be broken into two main categories: naturally occurring and manufactured. The naturally occurring types refer to reverberation heard in spaces or rooms. The most common manufactured types come from physical devices – the spring reverb and the plate reverb. WELCOME TO MY CHAMBER
One of the earliest and simplest ways of creating reverb after the fact was to play a sound source back through a loudspeaker placed in a reverberation ‘chamber’, then rerecord the resulting sound back to tape. These chambers could be either a specifically designed reflective space, or an existing, adapted space. Variations could be made by using different materials on the surfaces, different sized rooms, and by varying the distance from the mic to the loudspeaker.
Chambers built below Abbey Road Studios were used by The Beatles for vocal effects. John Bonham got the drum sound on Led Zeppelin’s “When The Levee Breaks” by setting up at the base of a stairwell, while mics were placed at various points above him. HAIL THE HALL
Hall reverbs simulate the sound of real, existing halls of various shapes and sizes. There’s usually a cluster of initial reflections followed by a long decay time of between 1.2 and three seconds, with a high frequency roll-off over time. Many famous concert halls around the globe have been sampled for use in digital reverb units and plugins – these types of reverb can add ambience and depth to a mix, sustain notes, and create a sense of depth and ‘majesty’. Overuse or misuse on
unsuitable sources can create mud and boom, and generally wash out a mix.
Room reverbs, as the name suggests, are created to simulate the sound of various types and sizes of rooms, taking into consideration the surface materials as well. The smaller rooms mean faster decay times and less boom. Room reverbs are generally used to put a very dry signal into a more 'live' space. It’s often the case that in a smaller budget studio, it’s easier to create one dry, non-reflective, multi-purpose recording space then apply an effect to that signal later. Otherwise, everything you record will essentially sound the same. You can add reverb to a dry track, but you can’t take it off a wet track.
Small room reverbs can also be used as a kind of slapback echo: try using a short decay, then dial in a little bit of pre-delay to get a quick reflection. Overdoing short reverbs can make a recording sound like the mics were too far away from the instruments, though, and work negatively on clarity and focus.
FILL UP YOUR PLATE
A plate reverb is literally a steel plate suspended under tension by springs in the corners where the plate attaches to the outer shell or frame. The plate vibrates via a signal from a transducer, and the vibration is sensed elsewhere on the plate with a contact microphone. Tapping a large metal plate and placing your ear in close proximity will give you some idea of the way this works.
Plate reverbs don’t add the same kind of depth and ‘distance’ to sounds as hall reverbs. They tend to almost merge with the source to reinforce it, rather than throw it into a space. Thus, they can make vocals sound fat and lush, while making a snare more powerful and adding character.
SPRING IS IN THE AIR!
Like plate reverbs, spring reverbs work by sending a small signal through a spring inside a casing. The signal is reflected back and forth through the springs with a delay determined by each spring’s diameter, wire gauge and length. The moving magnets of the output transducer generate an alternating magnetic field, which induces an electrical signal in the output transducer coil.
Spring reverbs are common in traditional guitar amps, and most guitarists will be familiar with the raucous sound the springs make just from lifting or moving the amp while it’s powered up. They're generally used across electric guitars or keyboards to add character.
As the name suggests, these reverbs create the sound of a reverb that starts with the decay and finishes with the initial attack. Thus, it starts quietly and progressively gets louder. Back in the day, the only way to do this was by cutting the section of tape with the reverberated sound on it, then flipping it and splicing it back in. Of course, when digital reverbs came in, it could be done with the flick of a button, and the effect was very fashionable for a time. It’s worth a look if you’re chasing something a little different for effect.
SHUT THE GATE!
Gated reverbs are created by inserting a noise gate in the chain after the reverb, in order to abruptly cut off the reverb’s tail. This was very popular in the '80s – it would be placed over snare drums to fatten the tone and add colour. The reverb decay time and the gate threshold were adjusted to suit the song’s tempo so that the decay didn’t continue across the next beat.
THE CONVOLUTION REVOLUTION
This is a maths-heavy, digitised reverb that uses samples, or impulse responses (IR) of real-life acoustic spaces. An impulse response, in this case, is a representation of how a signal changes when going through an acoustic environment. Convolution reverbs are relatively new, due to
their complexity. They are able to accurately simulate reverb and sound very natural. That being said, they can be a little heavy on a computer’s processor.
This is a digital reverb that creates echoes using mathematical algorithms to simulate the delays that occur in reverb. Synthesising the echoes rather than using actual samples, like a convolution reverb, is much easier on the processor. The trade-off is that they rarely sound as natural as a convolution reverb, so it's best to use a convolution reverb for the most important parts, and then an algorithmic reverb for less exposed sounds.
Here’s list of typical parameters to check out: Using pre-delay is a great way to put a tiny space between the source and the reverb, so that the attack of the notes is not swamped out. Decay literally controls the length of the reverb. Diffusion refers to the amount of time is takes for the reverb to convert from early reflections into full reverberation. Mix is used like a balance control to switch between the dry signal and a reverberated wet signal. If you’re using the reverb on an auxiliary buss, this would be set to full wet. If it’s been inserted directly over a channel, it’s pretty much a volume control for the amount of reverb you want. LPF (low pass filter) will roll off the high frequencies at a chosen point as time passes. This is used to shape the tone of the decay. HF Cut controls which frequency begins to drop off first during the decay phase
KEEP BOUNCING OFF THE WALLS
In the next issue, we’ll look at applying and tweaking reverbs in a typical mix situation, as well as some DIY approaches to chamber reverbs and re-amping for effect.