Reverb has the unique ability to make instruments in the mix sound like they’re being played in the same room. Learn how to tweak your reverbs to get the most accurate sounding space for your song.
by Charles Hoffman
A reverb is an audio device that allows you to simulate the physical characteristics of a room and generate the reflections that would occur if you were to play a sound within that room. The specific properties of the room can be tweaked using the reverb’s parameters.
Originally, reverb was recorded, and not generated by an audio device. If you wanted your saxophone to sound like it was in a gymnasium, you would record a saxophone in a gymnasium. Alternatively, engineers would record the saxophone dry, play the recording back through speakers set up in the desired room, and record that sound with microphones. By moving the saxophone player or speakers around, applying various types of acoustic treatment to the walls and by experimenting with different microphones and microphone placements, you would eventually craft the sound you were looking for. It’s neither time efficient or affordable to record reverb in this way, but before the invention of reverb units, this is how it was done.
Hardware and software developers have figured out how to re-create the sound produced by various real and imaginary rooms. We won’t deal here with the technology behind different types of reverbs but rather, how you’re able to use them practically to create different room characteristics appropriate to your song.
Room Characteristics and Reverb Parameters
When attempting to simulate a room using reverb, you need to take characteristics like room size, shape and material into consideration. It’s equally important to determine where the sound source is stationed within that room. Where is the microphone that’s recording the room’s reflections positioned? Are there other objects in the room? These are some of the crucial questions that you need to ask yourself.
Much like other audio devices, there are a core set of parameters that will allow you to sculpt the sound produced by your reverb. These parameters usually include shape, decay time, size, density, pre-delay, a dry/wet knob and a filter section. For simple reverb units with a limited number of controls, some of these parameters will be pre-determined for you.
The Waves Abbey Road Chambers plugin is one of the most visual plugins I’ve found when it comes to room modeling. It provides a top-down view of the room you’ve selected, shows you where the speaker that is playing your input signal is located, and also indicates where the microphones are positioned in the room. Abbey Road Chambers even shows you the direction the speaker is facing and the type of microphones being used.
Manipulating Room Shape and Size
A room’s shape and size play a tremendous role in dictating how the elements of your song are going to sound within the space. Large untreated rooms typically result in sounds with long decay times, while small untreated rooms usually result in sounds with lesser decay times; this is actually a bit presumptuous because a room’s material plays a significant role in how reflective a room is, but we’ll look at this in more detail in the next section.
If your reverb has a shape control, it affects the pattern and spacing of early reflections. Early reflections are copies of the direct sound that you hear after they’ve bounced off your desk, walls, ceiling or floor, no more than once or twice. There is usually some overlap between early reflections and the diffused sound (sometimes known as the reverberant field), and the shape control allows you to manipulate the decay time of early reflections, dictating how much overlap occurs.
Decay time adjusts the amount of time it takes for the tail of a reverb to die out. If you’re unfamiliar with a reverb, look for the decay time knob because it’s going to allow you to get the unit under control. Shorter decay times will keep sounds upfront and present in your mix, while longer decay times will push elements to the back of your mix, making them seem further away.
Size determines how big the room is that a reverb is meant to model. Larger rooms, like concert halls, tend to produce longer decay times and darker sounds, while smaller rooms, like drum booths or Jazz clubs, often result in brighter sounds with shorter decay times. Some convolution reverbs will generate new impulse responses by resampling when you modify their size.
Manipulating Room Material
Most materials can be broken down into two categories: porous materials and non-porous materials. Insulation is an excellent example of a porous material. It contains tiny spaces that sound can leak into and get trapped in. Porous materials tend to be good at absorbing sound and the thicker the material, the more adequately it will be able to absorb low frequencies. Many control rooms have thick insulation panels hung on the walls, which help to absorb mid-high frequencies.
Non-porous materials like tile or metal tend to have poor absorption properties. They reflect sound across most of the frequency spectrum and can make a room sound “bright.” Natural materials like wood are somewhat neutral in the way they reflect sound. Wood is semi-porous, which allows it to absorb high-frequency content but also remain lively. The next time you walk into a wooden sauna, listen to how your voice interacts with the space; it should sound energetic, but not in the same way as it would in a tile bathroom.
A reverb’s density controls how thick the echoes are as your sound diffuses throughout the room. Higher density values can help make your input signal sound more aggressive, while lower density values can help separate the effect of the reverb from your original sound.
The filter section of your reverb plays an essential role in creating space between your dry and wet signal. I’ll usually apply a high-pass filter at 200Hz and a low-pass filter at 2000-3500Hz; this prevents my reverb from creating phase issues in my low-end and also cuts off the high-end that would otherwise make my reverb too bright. However, if I’m trying to model a “dark” space, I’ll cut away more of my top end and add back low end. On the other end of the spectrum, if I’m trying to emulate a room made of a non-porous material, I’ll refrain from cutting away my top end, and I may even boost it with a high-shelf filter.
Manipulating Distance from the Sound Source to the Microphone
Traditionally, when you record reverb, you set up a sound source like an instrument or a speaker playing a sound. A microphone is placed in the same room as the sound sources and then you hit record. Where you set up the sound source and the microphone is important. The further away from the sound source your microphone is, the more of the room you’re going to record. As well, moving your sound source around the room is going to affect how its reflections interact with the environment. Repositioning the microphone will allow you to capture different combinations of the direct sound and its reflections.
Pre-delay controls the delay time before your microphone picks up early reflections. Early reflections are sounds that reach the microphone after reflecting once or twice off the surrounding walls and/or ceiling. Pre-delay adjustment plays a considerable role in determining the apparent size of the room, although other factors like the shape and decay time come into play as well.
The dry/wet parameter controls the mix between the unprocessed input signal and the processed output signal of your reverb. If the effect of the reverb sounds the way you like but it’s overpowering your original input signal, dialing back the dry/wet parameter will resolve the issue.
How to Approach Creating a Realistic Room Sound
If you’re trying to model a specific room with a reverb, you need to think about all the physical properties of that room and how they’re going to affect the reflections the room generates. Modifying a single parameter on a reverb can change multiple characteristics of the room it’s meant to model. Revising parameters a number of times is usually required if you’re trying to model a specific space accurately.
Think of yourself as a sculptor slowly chiseling away at a stone, it takes lots of minor adjustments to achieve a beautiful finished product. Modeling a room using reverb requires the same attention to detail. If you try to do too much at once, you risk throwing off the careful balance between parameters, and consequently, the characteristics of the room.
Sometimes making your reverb wetter than is necessary can be useful for this step; it makes hearing the effect of the reverb significantly easier. Once you’ve done this, turn down the wetness of your reverb to an appropriate level and tweak your reverb’s settings further until you achieve the room sound you’re after.
Making Instruments Sound Like They’re in the Same Space
It’s important to note that if you use too many different reverbs in your song, the perceived space you’re trying to create will become less believable. If you’re trying to make it sound like your orchestral piece is being played in an extravagant concert hall, it doesn’t make much sense to use 5 different reverbs across various tracks, each modeling vastly different rooms.
One of my favorite mixing techniques involves setting up 2 aux tracks and placing a reverb onto each of them. On the first aux track, set up a reverb with a short decay time, and on the second aux track, set up a reverb with a much longer decay time. You can send most of the elements in your song to the first reverb, which is meant to create a cohesive space within your mix; the effect should be very subtle. The reverb on the second aux track should have a longer pre-delay value; you can send signal here from tracks that should have an exaggerated reverb effect.
Sometimes it’s fun to apply effects to the aux reverb tracks. EQ, compression and distortion are all great options. The Manny Marroquin Reverb actually allows you to apply these types of effects within the plugin itself; this will enable you to set up a processing chain within the plugin, and use the dry/wet knob to control the balance between the unprocessed and processed signals.
To practice sculpting reverbs, set up two audio tracks with the same source signal and apply a different reverb to each track. Choose a random reverb preset for one audio track and then try to emulate it manually using the reverb on the other audio track. You’ll be most successful with this if you choose two similar types of reverbs, such as two room, hall, chamber, plate or spring reverbs.
A versatile reverb like H-Reverb or Renaissance Reverb will get you pretty far, but having a variety of reverbs at your disposal is essential if you work professionally, and need to model many different rooms. Each reverb unit produces a unique sound, so multiple options expand your creative possibilities. You can view Waves full lineup of reverb plugins here.
Want more on mixing with reverb Get 8 reverb mixing tips here.
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