We often hear about SOUND GLUE.
It’s a term that appears everywhere in articles, Facebook posts, or YouTube videos discussing mixing and mastering.
I have used it quite a few times on my YouTube channel.
But despite the omnipresence of this word around us, it is often difficult for a mixing beginner to understand.
What are we really talking about?
What is sound glue?
How do we ADD IT?
All the answers in this article! 🙂
Sound Glue: Definition
Sound glue is a term commonly used in the field of audio mixing to describe the effect of cohesion and solidity that unites the different tracks of a mix.
It’s that feeling that all the musical elements, although distinct, belong to a homogeneous and coherent whole.
Sound glue transforms a group of individual tracks into a unified musical entity, thus giving an impression of professionalism and finesse to the mix.
Imagine a group of musicians playing in a room: if you listen to the concert, you inevitably feel that all the instruments are playing together; there is a unity that emerges from the concert.
On the other hand, when recording and mixing several tracks of different instruments separately, there isn’t always a similar cohesion.
This can be due to the treatments applied, but also to simple things like the fact that the instruments were not all recorded under the same conditions.
And it’s precisely this cohesion, this SOUND GLUE, that is often sought to be reproduced.
In fact, sound glue is the effect that makes all the instruments seem perfectly integrated and work together harmoniously, rather than sounding like separate elements recorded independently.
And to put it clearly, this sound glue is important because it can make the difference between a professional mix and an amateur mix:
- Cohesion — Sound glue helps to bind instruments and vocals, creating an overall harmony that makes the piece more enjoyable to listen to. Without this cohesion, a mix can seem scattered and disordered, with sound elements that do not integrate well with each other.
- Dynamic Uniformity — By using techniques such as compression, sound glue helps to balance the dynamic levels of different tracks, preventing certain elements from excessively dominating the mix and ensuring that each element finds its place.
- Perception of Quality — A mix with good sound glue is perceived as being of higher quality. Listeners tend to prefer pieces that sound unified and professional, even if they cannot precisely identify why.
Sound Glue: An Example
To better understand things, I have prepared a small example, which I hope will be as clear as possible.
However, let me warn you: even though I have exaggerated here, when we talk about sound glue, we are talking about something subtle.
In fact, it is closer to a feeling than to something very clearly audible.
In other words, we are not going to be dealing with something obvious, so:
- listen to the examples on good headphones or good speakers;
- if necessary, listen to them several times.
Here is the audio file that will serve as our basis:
As you can hear, it’s quite simple: we have a drum kit and a synthesizer.
What we can notice, however, is that it lacks cohesion: it feels like we have two tracks that are not really working together.
On one side, we have the percussion, and on the other, the synth.
It lacks density, cohesion, and connection between the instruments.
It doesn’t feel like everyone is playing “in the same room”.
Now, if I add sound glue precisely with compressors (we will talk more about settings later), we get this:
And now, it has changed the game: we have a piece with much more cohesion and density. It sounds immediately “better”.
Specifically, here are the things you can hear:
- because of the compression we brought out the punch of the drums;
- but above all, between the kick and snare hits, the quieter sounds have been raised in level. For example, the lightest cymbal hits are now more audible and their level has been smoothed out.
- the bass line played by the synthesizer seems stronger, and it is denser, rounder, heavier than before;
- overall, there is a greater sense of cohesion between the instruments, it feels more like a “finished product”.
Well, that’s what sound glue is: it glues the instruments together! 🙂
How to add sound glue?
But you still need to know how to add this sound glue!
You have several ways to do it.
First of all, you need to realize that above all, the aspect of “cohesion of instruments” comes from mixing.
That is to say, it is your way of mixing that will influence whether or not the instruments give the impression of playing together.
If you use a different reverb for each of your 50 tracks, for example, it is highly likely that you will not reinforce the cohesion between your instruments.
However, it is impossible for me to give you precise mixing advice on this point: it is really a matter of perception and artistic direction. There is not ONE mixing technique that would certainly ensure cohesion.
Except when we talk about processing on a buss.
A drum buss for example, or why not the master buss (in a mastering logic for example).
Indeed, if you have already mixed your track or a group of tracks and you want to give it more cohesion, you can apply processing directly on the buss to do so.
In fact, the parallel compression technique is an option that works quite well.
But, it is not the only one and I tend to recommend a technique based on classic compression by default.
Typically using an SSL type compressor, you can do interesting things using this kind of settings:
- low or medium ratio (less than or equal to 4:1 on this type of compressor);
- slow attack, to let the transients through (typically 30 ms on this type of compressor);
- fast or relatively fast release, to follow the variations of the music (typically less than or equal to 0.3 seconds on this type of compressor).
If you are not familiar with these settings, I recommend you check out my guide on using compressors.
And if you are not well acquainted with SSL compressors, you can watch my video below (but note that the technique is replicable with other types of compressors):
In short, with this type of settings, you will let the transients through thanks to the slow attack but compress what is BETWEEN the transients.
So you will smooth out the volume of the quieter sounds
As a result, since the dynamic variations of the quieter sounds are smoothed out, you will have the impression that these sounds become clearer, and these sounds will fill the space between the transients more densely.
You will then feel that the instruments gain in cohesion.
And you will simply have added sound glue to your track or group of tracks.
An explanation in pictures
To illustrate what we just said, I propose a little explanation in pictures.
Imagine that your audio signal from your master buss looks like this:
If we compress with a slow attack, we let the big transients through, but we compress what comes after.
As a result, the signal after compression will look more like this:
We have leveled the audio signal between the peaks, and in doing so we have brought homogeneity and cohesion to our mix.
So, we have added sound glue.
In conclusion
There you go, you have all the basics to understand the concept of sound glue well.
Little tip: right now, don’t hesitate to listen to the audio examples a bit higher up. Now that you have had the explanations, it might be a little clearer.
But also, feel free to experiment on your side with one of your tracks using a compressor.