As reverb is both a boon and a bane to music production, I have been engrossed in researching out what it actually is, when it is an effect. We hear terms like Plate, Spring, Impulse response. But what does it all mean and more importantly, how does it work? I didn't know, so I decided to find out. Definition
First thing I wanted to know was, what is it? We know that it is the effects of reflected sound. A lot of poor reverbs tend to be just that, a lot of reflected sounds. But, but a lot of the docs on the topic fail to mention that it is more than just that. It is not just reflected sound, it is passively radiated sound as well. Walls and floors
- Wood reverberates differently than concrete. Density of a material changes the sound dramatically, both in speed and in quality of transmission. A simple experiment. Go to another room and listen to your music (especially if you can go into the bathroom). At a distance, especially if there is no line of site. The sound will move through objects and be reflected around them. When it reaches you in the bathroom it is fundamentally changed. Speed
- When talking about sound traveling through more than one transmission medium, we hear the bass first, then the reflected sounds. Why? Because (again depending on material) the bass will actually travel through the solid (denser) objects faster than through the air, and may be radiated out from the walls, floor etc, before the higher end sounds reach you. Some materials will transmit and radiate lows but dampen the highs. Pure Echo
- A pure echo is a simple reflection. It is usually very clean, uncolored by the reflective source. Echo is only one part of the reverb equation. Pure echo will have a decay associated with it, due of course to distance. Reverberant Sound
- With reverberations, the reflected sounds are going through a metamorphosis due to the interactions with the reflecting materials. It will again filter and break up the sounds as they reflect off the surface (like light, a smooth surface will scatter the wave less). Each reflection drops the Db a corresponding amount based on both distance and material dampening effect.
So, reverberations are more than just the echo, and more than just the timing of the delay, but how they quantifiably color the sounds. If you could hear the reverb trail alone without the source, it will sound very different from an echo. It may be heavily distorted, or even unrecognizable. Types of Reverb in Recording
As we all know, there are a variety of reverb types that we use in recording. I will loosely cover them here. Discovering what each of them is, and how they work, enlightened me about why I dislike so many typed of reverb. Plate
: A plate reverb is just that. A box with a speaker in it that bounces sound off of a steel (or other material) plate of some sort and is picked up and amplified by a mic. Spring
: Like the plate, the sound is directed at a spring and the mic uses that as its source. The spring does not sound as nice as a plate, but is much smaller in size. This is why many guitar cabs use spring reverb. Convolution
: This is the modern approach to reverb effects in the digital world, and is where I will spend more of my time discussing as the answer to what it is, is a bit convoluted. Convolution Reverb Impulse response
: When researching this topic, the first things we find are all sorts of formulas about measuring the both the delay and the decay of any given reflection. These measurements, if enough are taken, could actually describe the room in great detail (think about sonar and radar imaging). The impulse response is both the change in time and volume, and carries the coloring information with it as well. It is in a sense, just the information about the room.
An impulse response is commonly generated using pink or white noise*. There is no musical information present within the measurement or recording of it. Refraction
: Refraction is the process where a signal is broken up into its corresponding spectral parts due to the interaction with a transmission material. This information can also be carried within an impulse response. Convolution
: This is where things get ugly. We start to see words like "Fourier Transform
", finite responses and so forth. Things start to look like math very quickly, and that is because it is. For the most part we users will never go into the math, but, it helps to understand a bit of the math in order to understand what the controls are doing (outside the basic ADSR).
Put simply, a convolution processor is kinda like a side chained compressor. A convolution reverb will take into account many aspects of the mathimatical properties of sound, and apply sophistocatic algorithms to generate the needed variables to then feedback to the user. It does math on both parts (the source signal and the impulse response) to generate a third signal that is based mostly on the original signal, but slightly modified. A great deal of this math is error correction (summing errors due to the number of samples and so on). Its primary function is to describe the effect to the system so the system can generate the desired response. This is similar to other reverb types, with the major exception of not requiring a feedback loop
So to sum it all up. A reverb is not just an echo, but a colored echo based on the room that is reflecting and refracting the waves. This is why it is both so powerful, yet so dangerous. The color has to be carefully thought out.
*pink noise is "static" like noise that jumps up on a per octave level. White noise is uniform and carries static noise information on all frequencies
If anybody has any corrections or additions, please feel free to add em.