SamplecrazeStretch That Note

Reverb - Part 1


Reverb is the most commonly used and abused effect and yet it is such a simple and versatile tool.
I think that the problem lies in the fact that reverb seems to be the ‘go to’ effect when trying to create the illusion of space and that most users seem to load a preset from the vst’s preset menu and mix to taste not knowing what is actually happening bar auditioning the resultant output. What makes it even more confusing is that most vst manufacturers will name their presets based on either the space that the reverb is trying to emulate or the sound that it is affecting. Although this is always a good starting point, for most users it can be a confusing path to go down.

Reverb serves a number of purposes and the two most important ones are that of ‘colour’ and ‘space’. It can also be used as a corrective tool, for example: helping to add tails to sounds that have been cut abruptly.

The type of reverb used is as important as how to use it. There are occasions whereby a certain type of reverb is required on a specific sound or mix because of its design and build: a plate reverb is a good example.

I will use different types of reverbs for the ensuing exercises and demonstrate how different they ‘sound’ and why certain reverbs are better than others at specific given tasks.
But before we even think of having some fun let us get the mechanics and physics out of the way and understand what reverb actually is and how it works.

We have been listening to music acoustically, for thousands of years. The natural acoustical space that the music was played in determined how the music was perceived. The environment and the materials that made up the surrounding environment had a huge impact on how the music was ‘heard’. We may think that we are the innovators when it comes to creating the right ‘space’ for music to be heard in but the Romans and Greeks had a head start on us and designed their amphitheatres and arenas to do exactly this. Some of their designs are truly impressive. Their understanding of space and the materials the space was constructed from is remarkable even today.

So, how does reverb work?

The listener hears the original sound, plus all the reflected sounds that come from the original sound reflecting off surfaces within the environment. These reflections are reflecting at varying distances and times. This is the nature of how sound moves in a given environment. As a result, the listener hears a composite of the original audio signal, the first reflections, and the delayed reflections.

These ‘signals’ will eventually lose their energy and dissipate.

Imagine a square room whereby you, the listener, are sitting in the middle of the room. For now, let us work under the premise that the sound that emanates from you emanates in all directions as opposed to being directional (which sound is). The room is made of brick walls coated with plaster. The walls and ceiling will have reflective properties. You shout. The shout begins to reflect from the nearest surface and ensuing reflections come from different angles at different times from different parts of the room. This makes perfect sense as the further away a reflective surface is the longer it takes the sound to reach it and reflect. The trajectory of the reflection depends on the angle the sound reaches the surface and the angle the surface is at, for example: a sound reaching one of the corners of the room at a 90 degree angle will reflect at that angle and reflect off another surface and continue to reflect until it dissipates or loses energy. A good way to imagine the reverb aspect is to think like this: after you have shouted the residual sound that remains is the reverb.
You can imagine what this means in rooms that have reflective surfaces, absorbing surfaces, irregular shapes and so on.
High frequencies are more prone to absorption and rooms with absorbing material (curtains, carpets etc.) will sound more muffled. Rooms with hard reflective surfaces will sound brighter and more brittle.

So, reverb is simply a term that defines the reflective properties of a given space and how those reflections are projected and processed.

Today, we emulate the space of the environment and use this in our music.

Our effects units can not only emulate real spaces but also create spaces that do not exist naturally in nature, like gated reverbs or reverse reverbs.

Figure 1 is a simple diagram displaying the various features of how reverb behaves. The terminology used has stayed the same for a long time although new features and therefore terminology has been introduced in modern day vst effects.

Fig 1

When the sound is triggered there is a pre delay just before the signal reflects off the first surface. The time taken for the signal to reach and reflect from the first surface is known as ‘pre delay’. In other words, the pre delay controls the amount of time taken before the reverb sound begins. By adjusting this parameter you can impress a change in distance. The longer it takes for a sound to reach a reflecting surface, the further that reflective surface is away from the sound source. This is the first stage in the reverb process.

This is then followed by the early reflections. The early reflections are the primary reflections after the pre delay and this is actually quite significant as it will denote the shape and size of the room before the decay sets in which in itself further defines the dimensions of the space. We tend to concentrate more on the pre delay and the early reflections to reference ourselves to our surroundings/environment than we do to the dissipation process of the ensuing reflections. The decay time (also known as reverb time) denotes how long it takes for the reverb sound to dissipate/lose energy, or die. The decay itself is equally important when gauging the surface absorption properties of the space. We can control the texture, length and behaviour of the decay in such a way as to create a new colour or to expose the surface material.
In most reverb units you will have a high frequency roll-off, sometimes referred to as HF damp. In natural spaces high frequencies dissipate quicker than low frequencies. By controlling this roll-off we can simulate the frequency dissipation. However, we can also manipulate this by using traditional filters post reverb. The depth and detail of control over these features allows us huge flexibility and scope to create interesting environments and textures/colours.

As the image in Fig 1 shows, there are a number of early reflections spaced out between each other. This is where diffusion comes into the equation. Diffusion parameters control the spacing in between the early reflections. The tighter they are packed together, the thicker the sound, and vice versa. The more diffusion you apply the thicker the reverb will sound. This can translate across as ‘dark’ or ‘confined’. If you apply less diffusion, the opposite happens; you space out the reflections further apart and make for a thinner reverb sound.

Part 2 - The Room and Reflections

Extract taken from Creative Effects