In this lesson, we’ll look at 5 of the most common reverb plugin parameters, what they do, and how to use them when applying reverb to your mixes.
What is reverb?
Before we examine what each reverb parameter does, it’s helpful to get a grounding on how reverb occurs naturally…
When an instrument makes a sound in a room, its sound propagates outwards, sending sound waves in all directions. A listener in the room will hear two types of sound. The ‘direct sound’ and the ‘indirect sound’, known also as reverb.
The first sound that a listener hears is the ‘direct sound’. This is sound that travels directly from the instrument to the listener.
Next comes the indirect sound. The indirect sound can be broken down into two parts. First are the ‘early reflections’, known also as ‘initial reflections’, or ‘pre echoes’. These are discrete reflections that have reflected from one or more surfaces, such as the walls, ceiling, or floor, before arriving to the listener.
After the early reflections comes the ‘reverberant sound’, known also as ‘late reflections’, ‘reverberant field’ or the ‘reverb tail’.
The reverberant sound is a collection of reflections that have bounced between multiple surfaces numerous times before arriving to the listener. These reflections are so closely spaced that the listener perceives a single merged sound.
Your brain uses the various characteristics of the reverb to decipher information about the space that you’re in, such as its size, its materials, how close you are to the instrument, and more. Accordingly, the various settings on a reverb plugin exhibit very specific characteristics in order to create realistic emulations of real spaces, e.g. church, hall, room, or of mechanical reverbs e.g. spring, plate.
Each of the parameters on a reverb plugin allow you to manipulate these characteristics. This allows you either to change the properties of the perceived space or to make the reverb more appropriate for your mix.
With this in mind, let’s examine each parameter…
Reverb plugin parameters: Pre Delay
The first reverb plugin parameter that we will look at is ‘pre delay’. Pre-delay controls the amount of time between the dry sound and the onset of the reverb. Changing the amount of time between the dry sound and the occurrence of the reverb can be used to control a number of things:
Pre-delay and depth:
Reverb plays a big role in the perception of depth. If an instrument is close to you, then you’ll hear the direct sound at a louder level than the reverb. The further away the instrument gets, the quieter the direct sound becomes in comparison to the reverb. So, when applying reverb in a mix, the more you increase the level of the reverb, the further away the instrument appears to be.
This can present a problem. Take for example vocals. Generally, you’d like to give vocals a healthy amount of reverb, but you don’t want to push the vocals to the back of the mix. You could turn down the level of the reverb to bring the vocals forward, but now the vocals sound too dry.
This is where pre-delay comes in. That’s because the perception of depth is not only governed by the level of the reverb in comparison to the direct sound. It’s also governed by the arrival time of the reverb following the direct sound. With pre-delay, you introduce a delay measured in milliseconds between the arrival of the direct sound and the arrival of the reverb.
The further an instrument is from you, the closer in time the direct sound and reverb arrive to you. That’s because the direct sound and reverb have had to travel a similar distance to reach you.
Whereas, when an instrument is close to you, the reverb will arrive after the direct sound. That’s because the direct sound has travelled a shorter distance to reach you than the reverb, which has travelled to the boundaries of the room and reflected off them before arriving to you.
So the longer the pre-delay, the longer the time between the arrival of the direct sound and reverb and so the closer the sound source appears to be. Whereas the shorter the pre-delay, the shorter the time between the arrival of the direct sound and the arrival of the reverb, and so the further away the instrument appears to be.
Accordingly, you can use pre-delay to apply reverb to an instrument whilst still keeping it towards the front of the mix.
Pre-delay and size:
Pre-delay can also be used to tailor the size of the space that the instrument appears to be in. Shorter pre-delay times give the impression of a smaller space. This is because it appears as though the sound does not need to travel as far to reach the nearest wall, ceiling, or floor to reflect from before it arrives to the listener. In turn, greater pre-delay times give the impression of a larger space. That’s because it appears as though the sound is having to travel further to reach the nearest boundary to reflect from.
Pre-delay and clarity:
Pre-delay can also be used to maintain a signal’s clarity when adding reverb to it. By its very nature, reverb has the potential to make things sound less clear and less defined. As such, allowing the reverb to occur too quickly in relation to the dry sound can potentially compromise the clarity and presence of the signal. By using the pre-delay parameter, you are able to delay the occurrence of the reverb. This retains the definition and the clarity of the dry signal.
Reverb plugin parameters: Decay Time
The next reverb plugin parameter that we will look at is ‘decay time’. Decay time represents the time it takes for your reverb to fade away to silence. You may sometimes see decay time labelled on your plugin as ‘reverb time’, ‘reverb tail’ or ‘RT60‘.
When thinking in terms of room acoustics, longer decay times will give the impression of a larger space, or of one which contains more reflective material, like brick, stone, or concrete. Shorter decay times will give the impression of a smaller space or one which contains more absorbent surfaces, such as carpet or drapes.
In practical terms for mixing, longer decay times can be more atmospheric. Shorter decay times are more controlled. When dialling in the length of the decay, it is important to ensure that your decay time is not so long that it causes the mix to lack clarity or feel washed out.
Reverb plugin parameters: Diffusion
The next reverb plugin parameter that we’ll look at is diffusion. Diffusion, sometimes labelled as ‘density’ or ‘shape’, usually controls both the dispersion/scattering of the reflections and their density.
With high levels of diffusion, the reverb sounds thick, warm, smooth, and washy. With low levels of diffusion, reverb sounds thin and sparse, often to the extent that discrete reflections can be heard.
Lower diffusion settings are associated with regular shaped rooms, or empty rooms, in which reflections bounce from surface to surface in a fairly consistent manner. Higher diffusion settings are associated with rooms that have an irregular shape or rooms that contain a greater range of surfaces and/or objects for the sound to reflect from, and for reflections to be broken up by, in turn creating a greater number of reflections with greater variation in their levels and spacing.
When applying reverb to your mix, highly defuse reverbs can sound impressive, but they can also cause your mix to lose clarity and sound washed out. So lowering the diffusion can be really useful in retaining definition and preventing the reverb from overpowering the mix. However, lowering the diffusion too much can make the reverb sound metallic, grainy, and chattery.
Generally speaking, lower diffusion settings are best suited to things like vocals, strings or other sustained sounds, as this helps to prevent things from sounding washed out. Meanwhile, drums and other percussive sounds benefit from higher diffusion settings. Higher settings make percussive sounds come across as big and thick, whereas lower settings can make them sound metallic and thin.
Some plugins will allow you to control the dispersion and the density of the reflections separately.
Reverb plugin parameters: Damping
On your reverb plugin, the ‘damping’ parameter, sometimes called ‘absorption’, controls the absorption of the reverb’s high frequency content. It does so by controlling the reverb’s frequency content over time.
High damping values provide more high frequency absorption. Low damping values provide less high frequency absorption.
Most commonly, a reverb’s high frequencies decay faster than its low frequencies. That’s because high frequencies are more easily absorbed than low frequencies. The more absorbent the surfaces are in a room, the quicker the high frequencies will be absorbed. As such, the more high frequency damping you apply to a reverb, the more absorbent the surfaces in the room appear to be.
In the context of a mix, lower damping values create brighter reverbs, whilst higher damping values create darker reverbs. In a practical sense, applying damping can help to eliminate sounds that may sound harsh in the reverb’s high end, like vocal sibilance or scratches on guitar strings. Of course, if there’s too little high-end, the reverb may sound muddy and lack definition.
Some reverb plugins will offer you both a high frequency damping parameter and also a low frequency damping parameter. This is used to control the way the reverb’s low frequencies decay over time.
As well as damping controls, reverb plugins sometimes have other EQ controls built-in, such as a pass filter. Such EQ controls could be there to EQ the signal on the way into the reverb plugin to control which frequencies are sent to the reverb, or they could be there to EQ the signal coming out of the plugin to EQ the reverb itself. Such EQ controls could be included in addition to, or instead of damping controls. The key difference to understand is that these EQ controls do not affect frequency content over time in the way that damping does.
Reverb plugin parameters: Wet/Dry Mix
Finally, an important reverb plugin parameter to be aware of is the ‘wet/dry mix’, sometimes referred to simply as ‘mix’. The wet/dry mix parameter allows you to control the blend of the dry signal and the wet signal, the wet signal being the reverb. In most applications, 0% means you will hear only the dry signal with no reverb. 100% means you will hear only the reverb and non of the dry signal. At the 50% position, you will hear equal parts dry signal and reverb.
Most commonly, between 0% and 50%, the dry sound remains the same and the reverb is increased in level. At 50%, the dry sound and reverb are both at their highest level. Then, between 50% and 100%, the reverb stays at the same level and the dry sound is turned down. If you are adding your reverb plugin as an insert directly onto a track, then you will need to use the wet/dry parameter to define the blend of the dry signal and the reverb.
If you are adding your reverb plugin to an auxiliary track, then things are a bit different. In this case, you will need to set the wet/dry parameter to 100% wet. That way, the auxiliary reverb channel will produce only reverb. You can then send dry signals to it using an auxiliary send.
Keep in mind that, as we touched upon earlier, the more you increase the level of the reverb, the further away an instrument appears to be. If the reverb is louder than the dry signal, intelligibility is reduced.
So, those are the 5 parameters most commonly found on reverb plugins. Using these 5 parameters, you can tailor your reverb to create the sound that you’re looking to achieve. Of course, the exact parameters that reverb plugins offer can differ greatly between different plugins. The 5 I’ve mentioned here are the 5 that I focus on most when using reverb. Nevertheless, there are a few more that I will quickly mention, just in case your plugin happens to offer them…
Early Reflections and Reverberant Sound:
Earlier, we established that reverb can be broken down into early reflections and reverberant sound. Some reverb plugins allow you to control the level of the early reflections and the level of the reverberant sound as two additional parameters. The early reflections tell our brains a lot about the kind of space that we’re in. They also tell us how far away from us an instrument is. The quieter the early reflections are in relation to the direct sound, the closer to you the instrument appears to be, as the reflected sound has had to travel further to reflect from a surface and then reach you than the direct sound does. The quieter the early reflections are, the larger the room appears to be, because the sound has had to travel further to reflect from a surface and then reach you.
One trick when these parameters are available is to turn the level of the reverberant sound down, sometimes completely, leaving only, or predominantly, the early reflections. This can be used to add ambience, and liveliness, without adding wash. Alternatively, to get closer to a spring or plate sound, you could silence the early reflections, as neither plates nor springs exhibit early reflections.
In addition, some reverb plugins offer a ‘room size’ parameter, sometimes simply referred to as ‘size’. Perhaps the most self-explanatory parameter, this allows you to control the perceived size of the space that is being emulated. Sometimes this will be a dial. Sometimes you will have predefined options like small, med and large. The changes in the perceived size of the room are achieved by changing the nature of things like the early reflections, decay time and pre-delay.
As you can see, taking control of these 5 reverb plugin parameters gives you a great amount of control over the way that your reverb sounds. This allows you to tailor your reverb to suit your mix. How do you like to use reverb in your mixes? Leave a comment below.
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