Most of the time, layering is used to obtain complex, moving, lively sounds. 

By combining multiple timbres, we obtain the equivalent of a soundscape. And this combination is a real work of research and sound shaping: you have to determine which elements work well together, mix them carefully and give them the right scope.

So there are several essential phases:

1- sound design of the layers

2- tonal placement of the layers

3- mixing the layers

This is a real job of mixing to achieve a unique sound.

To create the overlay we're interested in, we'll go through the initial phase of producing each layer separately. 

So we choose a direction for each layer and roughly start to give it a shape. 

Once we have a few interesting layers, we need to refine them in relation to each other. This is when you realise whether the direction you've taken is valid or whether it will lead to unusable or uninteresting results. 

It's much easier to start layering with different sources. For example, a base of analogue oscillator, a pinch of wavetable and a touch of FM. 

For the result to work, the role and position of each layer must be defined. To avoid producing an unusable sound mush, an interesting practice is to choose one layer to provide the fundamental and leave the other layers to provide the harmonics. This is obviously a very simplistic approach; in reality, there's no question of slicing up the frequencies to such an extent, otherwise the result will be aggressive and unusable. 

But the idea is a good one: to distribute the frequencies among the layers.

So we'll start by using various filters and EQs.

Secondly, you need to position the sounds in the sound field. You can pan Left-Right, but it's even more interesting to work in Mid-Side. M/S is extremely powerful for this kind of task. It will be the subject of a separate article.

Using M/S allows you to place sounds more precisely by treating the Mid and Side channels separately. This opens the door to equalisation that is better suited to complex layering. For example, you can attenuate the low frequencies of the Side channel while leaving them present in the Mid channel. You can use this technique to make the sound more massive where you decide. For example, there's nothing to stop you emphasising the Side channel and strongly attenuating the Mid channel.

We therefore assign a Mid/Side encoder to each layer, then install Mid/Side decoders on two busses to which we route the layers. The layers no longer go directly to the Master, but are routed to the new busses.

By adjusting the gain of these busses and adding selected treatments, you can change the feel of the layering. By listening carefully, you can specify the amount sent to Mid and Side for each layer.

One of the great advantages of layering is its ability to create movement. 

Once the Mid/Side pre-mix has been done, it becomes easier to set some layers in motion. This is how you can animate the sound, using carefully selected modulations (LFOs, etc). You'll inevitably think of PWM parameters for oscillators, carrier parameters for FM, and so on. But that's not all, since animated filtering can also be a great asset. An interesting approach is to use a band-pass filter rather than the classic LPF. By animating the band-pass frequency range, you instantly get a lively, organic result. The ideal is to install one on several layers and ensure that they do not follow the same movement. 

Of course, these filters should be installed before the Mid/Side encoders.

For layering to work, you need to check all the parameters regularly. It's meticulous work, but so rewarding. 

More often than not, ‘balance’ is seen as synonymous with ‘left-right’. This is not the case here; we will use the term ‘balance’ in its tonal sense. 

We'll also be looking to animate and develop the frequency balance. This will ensure that the sound is not just one big rigid pad. We won't hesitate to momentarily highlight certain elements by modifying their equalisation. It's perfectly legitimate to want a layer to progressively go from Side to Mid, with a fuller bass. Layering is a form of pre-mixing a set of sounds before the final mix, and is the ideal opportunity to be creative and experiment.

Theory is all very well, but you need a lot of practice.

Practising layering, of course, but also and above all practising the sounds you create. It's the best way to make progress with your technique and to end up acquiring reference points. 

By playing your sounds, you develop your layering technique and your sound identity at the same time.

There are a few generic tips that don't hurt to follow. 

- add layers gradually
- use modulations after you have established an initial pre-mix
- build the sound in space, no spatial processing is forbidden
- think about the role of each layer and bear in mind that these roles can evolve
- equalizers are your friends, as long as you use them in attenuation
- Mid-Side is consistency
- play the pre-mix and each of the layers regularly during your layering work
- practise and try out everything you have available 

A final piece of very generic advice: avoid compressors wherever possible. Most of the time it's as simple as attenuating with an EQ and rebalancing with the track's gain.