Understand reverb
When we hear sounds in the “real world”, they are in acoustic space. For example, suppose you are playing an acoustic guitar in your living room. Not only do you hear the sound of the guitar, but because the guitar generates sound waves, they bounce off the walls, ceiling, and floor. Some of these sound waves return to your ears, which due to their travel through the air, will be delayed a bit compared to the direct sound of the guitar.
This sound resulting from all these reflections is extremely complex and is called reverberation. As sound waves bounce off objects, they lose energy and their level and pitch change. If a sound wave hits a pillow or curtain, it will be absorbed more than if it hits a hard surface. High frequencies tend to be absorbed more easily than lower frequencies, so the further a sound wave travels, the more “muffled” it sounds. This is called damping. As another example, a concert hall full of people will sound different than if the hall were empty, because the people (and their clothes) will absorb the sound.
Reverb is important because it gives a sense of space. For live recordings, there are often two or more microphones set up to pick up the sound of the room, which can be mixed in with the sounds of the instrument. In recording studios, some have “live” rooms that allow for a lot of reflections, while others have “dead” rooms that have been acoustically treated to reduce reflections to a minimum, or “live/dead” rooms that may have material sound absorbers at the same time. end and hard surfaces on the other. Drummers often prefer to record in large live rooms so that there are plenty of natural reflections; vocalists frequently record in dead rooms, such as vocal booths, and then add artificial reverb during mixdown to create a sense of acoustic space.
Whether generated naturally or artificially, reverb has become an essential part of today’s recordings. This article covers artificial reverb: what it offers and how it works. A companion article covers tips and tricks on how to make the best use of reverb.
Different types of reverb
There are two main types of artificial reverb: synthesized and convolution-based. Synth reverb “shapes” the sound of a room by using various algorithms. For example, a “Hall” algorithm will take into account that waves travel further in a concert hall than in a small room, so the reverb will take longer to decay. A “Room” algorithm might model a small room, such as a club or practice space. Other algorithms model artificial reverbs, such as the “Spring” reverbs found on guitar amps, or the “Plate” reverbs that were widely used in the ’60s. Each algorithm has a different sound quality, but they all basically work the same way. the same way: a signal enters the reverb, is analyzed, and the reverb algorithm generates echoes and reflections that mimic what is happening in the chosen acoustic space.
Convolution reverb is a relatively new type of technology that “samples” the sound of a room. Typically, a device like a sports starting gun will generate a pulse that creates reflections in a room. These reflections are recorded, analyzed and converted into a highly accurate model of that specific room. A good analogy is that the impulse of a convolution reverb is like a “mold” that sound is poured into, and the sound takes on the characteristics of being in that room.
You can think of the difference between synthesized and convolutional reverb as the difference between a synthesizer and a sampler. The synth will give more control over the sound but will have a more “impressive” character, while a sampler provides an extremely accurate sound, but generally less editable.
Another consideration is that convolution reverb is a processor-intensive operation. Computers have only recently become powerful enough to allow real-time operation, and even then, you may experience some audible delays due to processing. Fortunately, since reverbs are delay-based anyway, with fast computers you might not notice anything objectionable.
reverb elements
A sophisticated reverb will have many parameters, but few people know how to optimize these parameters for specific recording situations. So, let’s discuss how the various parameters affect your sound.
Reverb has two main elements:
Tea first reflections (also called early reflections) consist of the first set of echoes that occur when sound waves strike walls, ceilings, etc. These tend to be more defined and sound more like “echo” than “reverb”. You can often adjust the level of early reflections.
Decay, which is the sound created by these waves as they continue to bounce around in space. This “wash” of sound is what most people associate with reverb and is often referred to as a reverb tail.
Other parameter, pre delay, sets the time for the first sounds to travel from the source to the first set of reflections. The larger the gap, the longer the pre-delay because it takes longer for the signal to reach a wall or ceiling and start bouncing.
Advanced Parameters I
The following are some of the parameters found in high-end synthesis-based reverbs; Less expensive reverbs will have a subset of these parameters. Convolution reverbs generally have fewer parameters, but in recent years, engineers have figured out how to make convolution reverbs more editable.
algorithm. We’ve already mentioned hall and room algorithms, as well as algorithms that emulate “old” synthetic reverbs. But you can also find such algorithms as cathedral, gym, small room, closet – everything is possible! There are even “reverse” algorithms where the decay builds up from zero to full volume instead of decaying from full volume to nothing, and “locked” algorithms that abruptly cut off the reverb tail below a certain level ( this effect was very popular in the United States). 80, particularly with the Phil Collins albums).
With convolution reverbs, the equivalent concept is called boost. Impulses can capture the sound of specific rooms (like particular concert halls) or even the sound of spaces like guitar cabinets. It’s even possible to create boosts from older reverbs, so there could be a boost that sounds like an old Lexicon PCM-70.
The size of the room. This affects whether the paths the waves take as they bounce around the “virtual room” are long or short. Like real rooms, artificial rooms can have “standing waves” and resonances. If the reverb sound has flutter (a periodic warbling effect), vary this parameter along with the decay time (described below) for the smoothest sound.
decay time. This determines how long it takes for reflections to run out of power. Remember that long reverb times can sound impressive on instruments when used solo, but they rarely work in an ensemble context (unless the arrangement is very sparse). The specification for decay time is called RT60, which means the time it takes for a signal to decay to -60dB of its original amplitude. For example, if RT60=1.5, it takes 1.5 seconds for the signal to decay to -60 dB or its original level.
Dipping. If sounds are bouncing off a room with hard surfaces, the reverb’s decay tails will be bright and “harsh”. With softer surfaces (eg wood instead of concrete), the reverb tails will lose high frequencies as they bounce, producing a warmer sound. If your reverb can’t create a smooth-sounding high end, introduce some damping to focus more on the mid and low frequencies. Listen to these two audio examples to hear the difference.
Advanced Parameters II
High and low frequency attenuation. These parameters restrict the frequencies that go into the reverb. If your reverb sounds tinny, try reducing the treble starting at 4-8 kHz. Note that many of the great-sounding plate reverbs didn’t have much response above 5kHz, so don’t worry if your reverb doesn’t provide high-frequency sparkle, it’s not crucial.
Reducing the low frequencies that go into reverb reduces confusion; try dimming from 100 to 200 Hz down.
Issuance of first reflections (sometimes just called diffusion). Increased diffusion brings the first reflections closer together, thickening the sound. Reducing diffusion produces a sound that tends more towards individual echoes than a wash of sound. For vocals or sustained keyboard sounds (organ, synth), reduced diffusion can provide a beautiful reverb effect that doesn’t overpower the source sound. On the other hand, percussion instruments like drums work best with more diffusion, so there’s a smooth, even decay rather than what can sound like marbles bouncing off a steel plate (at least with cheap reverbs). You’ll hear the difference in the next two audio examples.
The reverb tail itself can have a separate spread control (the same general guidelines apply for setting this up), or both spread parameters can be combined into a single control.
Early Reflections Predelay. A few milliseconds pass before the sounds hit the surfaces of the room and begin to produce reflections. This parameter, normally variable from 0 to around 100ms, simulates this effect. Increase the duration of the parameter to give the feeling of a larger space; for example, if you’ve dialed in a large room, you’ll probably want to add a reasonable amount of pre-delay as well.
reverb density. Lower densities give more space between the first reflection of the reverb and subsequent reflections. Higher densities place them closer together. In general, I prefer higher densities on percussion content and lower densities for vocals and sustained sounds.
Early reflections level. This sets the level of the early reflections compared to the overall decay of the reverb; balance them so that the first few reflections are not obvious, inconspicuous echoes or masked by decay. Lowering the level of early reflections also places the listener further back in the room and more towards the middle.
high frequency decay and low frequency decay. Some reverbs have separate decay times for high and low frequencies. These frequencies may be fixed, or there may be an additional crossover parameter that establishes the dividing line between high and low frequencies.
These controls have a large effect on the overall character of the reverb. Increasing the low frequency rolloff creates a bigger, “massive” sound. Increasing the high frequency rolloff gives a more “ethereal” type of effect. With few exceptions, this is not the way the sound works in nature, but it can sound great on vocals as it adds more reverb to sibilants and fricatives, while minimizing reverb on plosives and lower vocal ranges. . This prevents a “muddy” reverb effect that doesn’t compete with vocals.
THE NEXT STEP: APPLY REVERB
Now that we know how reverb works, we can think about how to apply it to our music, but that requires its own article! Therefore, please refer to the article “Application of Reverb” for more information.