On the subjext of natural, not special effect reverbs…While I am definitely not trying to say this should be done as a rule, I personally like a mix to simulate a virtual room. It is the way we are used to hearing real life things so I simulate it, or simulate it on the parts not recorded in a real room.
This is from a blog post I did for a local studio about natural reverb techniques.
2D Sound in a 1D System
Most humans live in three dimensional space - up/down, left/right, front/back. Typical audio systems have two channels - left/right… think of our ears as being two left and right inputs.
If we only have one dimensional hearing, how can we hear in two dimensions? If you were in a completely anechoic space, a space with no reflections, it would be much harder. (Interestingly, artificial rooms like this make people anxious and even hallucinate- google ‘Anechoic Orfield Labs’ for e.g.
In natural spaces, however, we do perceive more than one dimension. Left/right is easy. Tap something to your left, the sound reaches your left ear before your right ear. Your brain makes a calculation based on this.
Near/far is more complicated. In short, we perceive it through environmental clues.
If you have ever looked at a reverb pedal or plugin, you may know the terms pre-delay, dampening, mix, time. But let’s examine where those come from. Many people turn these knobs and aren’t clear on how they relate to perception of distance. Understanding this can help you use these effects yourself or in critically listening when working with an engineer.
First, a brief history of reverb.
Humans long enjoyed the natural reverb characteristics of caves, cathedrals, public baths, and dungeons. Our first artificial ‘analog’ reverb units used springs or plates. Spring reverbs are still quite popular in guitar amps; think of the iconic surf reverb sound. Digital reverbs have come much closer to simulating natural spaces.
I tend to think of using reverb in two ways - to simulate a natural room or as a special effect. As a special effect, I might use a huge wash of reverb on guitar in place of a synthesizer pad. Or I might use a reverse reverb on a track - a sound that doesn’t occur naturally in our time-space dimension.
With special effects, of course, there are absolutely no rules. In simulating a natural space, some understanding is helpful.
Before we get to effects, you want to consider how you will record things. If you have a nice sounding room, you might want to put the microphones farther away to capture more of the room’s reverb. On the other hand, you might want to close mic them because some elements, e.g. a synth, might be overdubbed directly, or you might want to close mic things for isolation. There, you might want the freedom to add similar reverb to each element to glue the mix later. Granted, you can have some room mics on the drums and dial in reverb on the overdubs that matches it, but this takes skill and practice and is hard to get perfect.
With that background, here are the key parameters that help us perceive distance, our second D:
The farther something is from you, the smaller the difference is between any left or right signals. Image a 20 meter long room. You are facing the drums. The low tom is on the left, hi hat on the right. If you are at the far end, the angles to your ears may only be a few degrees. If you move the drums to a meter in front of you, they may be at 45 degree angles to your ears, making it much more obvious which is to the left and right.
So anything intended to be far away should be panned more to the center. Close items can be panned anywhere, those are just perceived as being to your left or right.
Imagine again you are in the back of a room, a singer is in the middle. When they sing, the sound of their voice will go straight to your head. That is the ‘dry’ signal. Their voice is also radiating in multiple directions, off the walls, the ceiling, and the bass player’s vinyl pants.
The pre-delay parameter adjusts the delay between the dry signal hitting you and the wall or ceiling reflections. If the singer is farther back in the room, some of the reflections would hit you much closer in time to the dry signal. If a guitar amp intended to be at the far wall, you might use a pre-delay of near zero.
If you are trying to match overdubs or a specific hypothetical room, note that three milliseconds is about 1 meter. You might look at your plugins or hardware at this point, ones you are familiar with. That is probably pretty low on the dial. A lot of reverb effects are meant to go well beyond studio or even concert hall sized spaces.
Reverb Mix or Wet/Dry- Far away sources tend to have more reverb overall. There is more opportunity for more reflections on the way from the source to you. In some scenarios it can even mask the dry signal - remember the way it sounded when you locked your accordion player in the basement? Raise the reverb mix to move items farther away.
Equalization or ‘Damping’- High frequencies get absorbed more easily than low frequencies. So things that are farther away will have a high frequency cut or added dampening. It is difficult to give a default starting point here. I may use anything from 1000Hz to 6000Hz, but that is as much subjective taste as near-far positioning as different surfaces absorb frequencies at different rates. I also often set it a bit different for the near left and right because many real rooms will be filled with different junk that changes this.
At the other end of the frequency spectrum, you tend to have a tighter window of what is cut. A roll off up to 200Hz is not unusual.
Decay Time or Room Size - Things will tend to be perceived as farther away if the virtual room is larger. This one is more obvious, but note that if you are trying to glue your mix, having a long decay on some tracks and a short one on another will sound unnatural. A slight variation though just makes the room sound irregularly shaped. Remembering regarding pre-delay that three milliseconds is about a meter, note that big concert halls may have just 2 seconds of decay.
My advice having hopefully gained some understanding of these psychoacoustics, is to pay attention to these factors in your natural environment.