10. Reverb
Reverberation is the result of sound waves bouncing off many surfaces, such as the walls, the floor or the ceiling. It is actually present in any sound we hear in our everyday life so we don't always pay attention to it.
But when a sound is played in a room, or in any space really, we perceive the direct sound from the source, followed by the reflections of that sound off the surfaces in that space. When the time between these reflections is long enough, it create an echo effect, where we can hear the original sound repeating several times. This is what a delay does, which is an effect we'll see in the next video.
But when the time between these reflections is short and scattered enough, they blend and create kind of a trail of sound, this is what we call reverb.
So reverb effects are audio effects that are designed to emulate this type of reflections, and it is good to "place your sound in a particular space".
In a studio environment, when we record an instrument or a voice, we often try to eliminate as much of these reflections as we can, with acoustic treatment like foam panels.
But in the context of a song, a dry recording, without any reverb, can sound thin or unnatural.
So why do we tend to eliminate all this natural reverb when we're recording in a studio?
Well it's because it allows you to clean your recording before it goes to a reverb. Because a reverb would take all the frequencies in the sound and kind of scatter them in the frequency spectrum. So if you can remove unwanted frequencies or noises before applying any reverb effect, it would be easier to have a clean mix.
So reverb effects are designed to emulate the reflections of the sound in a space, and there are several ways to achieve that.
CHAMBER REVERB:
Chamber reverbs were originally made by placing a speaker and a microphone in a room, that way you would directly record the sound reverberating in a real room.
The name of the effect would then change depending on the size of the room.
Studio reverb for a very short one, room reverb when it's a little longer, up to hall reverb for very big spaces.
Nowadays it is way easier to recreate this effect with softwares, which we'll get into in a minute
PLATE REVERB:
Or you could create a plate reverb, by playing a sound through a metallic sheet, then recording the resulting sound with contact microphones attached to the plate.
Basically imagine a speaker that instead of vibrating a cone to produce waves of different air pressures, it makes a big sheet of metal vibrate, so the metal sheet will distort, altering the sound in the process. And that creates an effect very similar to the reverb of a room.
But there are still some differences between a plate reverb and a chamber reverb though.
Sound travels way faster in metal than in air, particularly for high frequencies.
So with a plate reverb, which makes the sound travel in metal, you will hear the higher frequencies slightly before the lower ones.
And because of a psychoacoustic phenomenon called precedence, we hear the overall sound as brighter.
So plate reverbs are cool to make something sound brighter without actually boosting the high frequencies, that's why it's used a lot on vocals or acoustic guitar for instance.
And the fact that sound travels in metal faster also makes the time between each echo way shorter, this makes this reverb more dense and also more consistent overtime.
SPRING REVERB:
In a similar way you can run the sound through a metallic coil to create a spring reverb, which is a popular effect for guitars.
When a sound travels through the spring, it bounces back and forth, which create a succession of rapid echoes. It's the succession of these echoes that makes the tail of the sound, that makes it sound like a reverb.
The fact that the sound needs to travel the distance of the spring back and forth to create each echo makes the time between each echo longer, which gives the spring reverb kind of a bouncy quality.
The way the spring vibrate also affect the frequency response of the signal, which gives the spring reverb it's particular sound.
In fact sound waves need to travel along the coils of the spring, so they move the coils one after the other to move forward. And low frequencies, with their longer wave length can make several coils move at a time, which allows lower frequencies to travel faster than higher ones, which mean we'll hear the lower frequencies before the higher ones. So the resulting sound will seem darker.
Now not everybody have the space or equipment to create these kind of reverbs mechanically. And this is where software come into play.
There are actually 2 ways of recreating reverb with softwares. There are algorithmic reverbs and convulsion reverbs.
ALGORITHMIC REVERBS:
Algorithmic reverbs are softwares that work only from their own internal algorithms, so they are generally less accurate when it comes to realism, but they are also lighter on the CPU. They can be designed to replicate a chamber reverb, a plate or a spring reverb, but they can also be design to do more creative stuff.
Like a shimmer reverb that pitches up every echo slightly, so the trail of the reverb would go up in pitch, giving a bright tone.
Or the other way around, the trail could go down in pitch to give a darker tone.
CONVOLUTION REVERBS:
Convulsion reverbs on the other hand work in pair with a particular type of file called "impulse responses", which are like the fingerprints of a room or a piece of equipment that exists in the real world.
Basically to create an impulse responses, of a room for example, you take a very short impulse sound, like one sample long, a very short burst of white noise. Then you play it in the room you want to create an impulse response file for, and you record the reverb with a microphone.
This recording you made is the impulse response. Then all you have to do is to put it in your convolution reverb and it will emulate quite accurately the reverb of the room you recorded in.
Convolution reverbs are actually the most accurate when it comes to recreating reverb of real-world places.
And the beauty of it is that you can also generate impulse responses for other equipment than a room. You could create IR files for a spring reverb, for a plate reverb or even for guitar amplifier. Softwares that emulate guitar cabs use the exact same technology.
And it goes even deeper. Because impulse responses are typically WAV files. So you could load your own sounds in a convolution reverb to see how it reacts and use it as a sound design tool.
This is a deep rabbit hole to explore so I'll may do that in a separate video as this one will be quite long already.
So in Ableton you can find a free convolution reverb as a max4live device simply called convolution reverb. It's part of the essential pack that comes with ableton 10. It already have a lot of impulse responses in it, but you can still add your own to have more (or if you want to use it as a guitar cab emulator.
So how do we actually use these reverbs?
Were going to see the main parameters you're likely to see on every reverbs and how they affect the sound, and then we see some tips and tricks to get the most out of them.
I'll be using ableton's stock reverb for the demonstration which is an algorithm reverb.
There you have a dry/wet knob, that allows you to mix the dry signal, not affected by the reverb, with the wet signal.
And then the main parameter of any reverb I guess would be the decay time, which will set the length of the reverberation. So a longer decay time makes a longer tail of sound.
Next to that you also have a stereo knob to make the reverbed sound more or less wide in the stereo field, and a size knob to emulate either a smaller room or a bigger room.
So generally a smaller size would work fine with a smaller decay time and a bigger size would work fine with a bigger decay time. But you can also make more surreal effects with a small size and big decay time or example.
Note that this reverb also have a setting of economic, medium and high quality that can change the way the reverb sound.
So don't hesitate to play with that, as even on high quality, it is still quite cpu friendly.
Another parameter your likely to see on many reverb effect is the predelay knob. It is basically a delay time between the dry signal and the first echoe of the reverb.
A short predelay will make the sound appear closer to the walls of the simulated room. And a longer predelay will make the source of the sound appear farther away from those walls and closer to the listener.
And lastly, I want to talk about the Reflect and the Diffusion knobs.
The Reflect knob, often called Early Reflection, sets the level of the first group of echoes. These early reflections are usually more defined than the rest of the tail, it sounds kind of more like a delay than an actual reverb.
So turning up the early reflection knob usually works better on sustained sounds like vocals or pads. And turning it down places the sound further back in the room, which often sounds better on more percussive sounds.
And the diffuse knob sets the level of the tail, so you can have more control over the balance between the tail and the early reflections.
I won't go in details on all the features this reverb has, because it is not a tutorial on this particular reverb, but instead, let's see some tips on how you can use reverbs in general.
HOW TO USE REVERB
One thing to keep in mind is that every frequency will be scattered in the frequency spectrum once it's processed by a reverb.
So it's a good idea to place an EQ before the reverb to get rid of problematic frequencies. It's always easier to clean a sound before a reverb than after.
And you can also put an EQ after the reverb to make it sound as you like.
That's why in ableton's reverb you have 2 simple EQ. One to filter the sound before the effect and one after.
Reverb is a nice effect to make a sound wider, by putting the sound in a space. But when you use reverb on a sound, it also makes it appear more distant, farther away from you, the listener. So it is a balance you want to keep in mind while using reverbs.
One thing I like to do to have more control over the reverb, is to create a parallel track for it. So basically in ableton, I would create an effect rack with two chains. One chain with no effect, that would be my dry channel, and one chain with a reverb set on 100% wet. Then I would play with the volume of each chain to set the balance I want (setting both chains at -6dB is a good place to start. It compensates the gain in volume due to having 2 chains playing at the same time).
You can also link one of the effect rack's macro knob to the chain selector to create a new dry/wet knob for this effect rack.
Having these two separate chains allows you to process the dry sound and the wet sound separately and more freely.
For instance you can put a compressor on the wet channel, to make the reverb a bit thicker.
You can even use sidechain compression and take the dry signal to trigger the compressor. This way the reverb will appear only after the dry signal, because the dry signal will duck down the reverb when it plays. And you can play with the release of this compressor to adjust how fast the reverb commes back in after the sound has stopped playing.
You can also add your own EQ before and after the reverb which would give you more control than the built in EQ. It is really useful to control the colour of you reverb so it would fit the mix better. For example if you have some prominent frequencies in the original sound than can cause problem once it's put through the reverb, you can tame them before hand. Then the second EQ is there to shape the overall colour of the reverb.
Speaking about the EQ I often prefer to cut the lows in the reverb, as reverb on low frequencies tend to cause chaos in a mix. But there are some exceptions to that.
You can also use a reverb on a return track. So you could send any of the tracks in you song to that reverb, and each one with a different value. So you would have all of your tracks unaffected by the reverb, layered with a reverbed version of themselves. And because these reverbed versions all come from the same reverb, it's a good way to place all your instruments in the same space. And this common space, this common acoustic characteristics would tie everything together in a coherent way.
And because this return track is its own chain, you can also use EQs, compressor or other effects to shape this reverb as you like.
These all work is the context of both mixing and sound design. But on the sound design side, you can also simply use a reverb to add a tail to a very short sound like very short drums to make them a bit longer. This works really well on snare drums for example.
Some reverb also have a freeze option. It will hold the sound of the reverb, so you can have sound that sustains forever. It's cool to make a long sound to resample and to use as a starting point for a new sound design.
Another thing I like to do, that is less conventional, that I took from techno music, is to use parallel reverb on a kick.
Basically you would create 2 parallel chains with an effect rack, just like we did before, with a reverb in the wet channel. And then you want to add a low pass filter before the reverb, so it would affect only the low frequencies.
It is a good trick to add some boom and some humpf to a kick, and I found it sometimes more effective than parallel saturation or parallel compression to give this extra thickness I wanted.
This is one of those weird tricks as generally, putting a reverb on low frequencies is considered a bad practice, because you want to have the bottom end of your mix in mono. But you can still add a utility effects a drag the width knob to 0 to make it mono.
With this one is can be good to use a sidechain compression triggered by the dry signal. This way you would hear the rumble after the kick has stopped playing, to keep it a bit cleaner.
The thing to keep in mind here is that it would add low frequencies, so if you have a bass playing in the same range, the two could clash. So you could keep this trick for tracks where there's not too much happening in the very low end, or you could have to EQ that cuts the low end of your bass so it doesn't clash too much with it.
One last thing I wanted to add is a very popular trick on how to use the predelay, I think it's too important to not include it here.
Let's take this chain we made for the kick as an example. We could use the predelay to make the reverb come an bit later, to add this bouncy feel to it.
Sometimes you want to have this predelay time synced to your tempo so it would kick in after exactly a 16th note or a 8th note.
So to do that you need to find how many milliseconds exactly is that 16th or 8th note.
Here's how to calculate it easily.
Your bpm gives you the number of beats that are in one minute. These are the quarter notes.
You also know that in a minute there are 60 seconds, that 60 000 milliseconds per minute.
So you need to divide these 60 000 milliseconds by your bpm, to have the length of one quarter note.
At 120 bpm, a quarter note is 500 ms.
Divide that by 2 and you have the length for a 8th note. That's 250 ms
And divide that by 2 again and you have the length of a 16th note. That's 125 ms.
So if you want to hear how the reverb sounds with a predelay of a 16th note. You can set the predelay to 125 ms.
And if you want a predelay of a 8th note, that would be 250 ms.
So you can use this predelay knob to add some bounciness to your tracks. Using it in this way essentially makes a slap back delay effect, which is something well see very soon, in the next video, when we talk about delay effects.
