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A Guide To Modulation And Modulators

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When using synthesisers, samplers or drum machines, one of the key ways of making your patches dynamic is the use of modulators. For many this is an area that seems complex and perhaps slightly daunting. The first thing to get your head around are the various types of modulators we use.

To ensure that the beginners amongst you grasp every area of the subject I’ve broken it down into easily digestible bite sized chunks. We’ll look at most of the common types of modulator used in most software based instruments.


Step 1 - What Is A Modulator?

Essentially a modulator is anything that changes something else in your mix. This is pretty general and covers a huge amount of different devices and systems. For instance mix automation that is effecting pan and level is actually a modulator and so is the knob on your MIDI controller used to tweak your favourite delay plug-in.

To narrow things down a bit we are going to be looking at modulators and modulation in software instruments. Usually this refers to synth engine based parameters and most of the controls we’ll be looking at here will be elements of a synthesiser.

Modulators at work in Thor’s Mod Matrix

I’ll cover each of the most commonly used modulators you are likely to find in your soft synths, samplers and loop players. Hopefully this breakdown will give you a good idea of whats going on ‘under the hood’ and equip you well when it comes to building your own patches and mapping modulators.

Most synths like Logic’s ES2 have a wide range of modulators on board


Step 2 - The Humble Envelope

One of the most common modulators used in any instrument is the envelope. This is a time based modulator that can control pretty much any parameter you like but it is most commonly associated with amplitude and filter controls.

Envelopes can have pretty much any number of points in them but again the most common configuration is the ADSR based envelope. This stands for Attack, Decay, Sustain, Release.

These four points are used due to the fact they can replicate the dynamic signature of most real world instruments. For instance applying an ADSR based envelope to the amplitude of a synthesiser and setting slow attack and release times a string or pad sound can be easily produced.

A slow ADSR based envelope producing a string patch in the Korg Polysix

The slow string sound in action

Just as setting slow attack and release can produce these slow moving sounds, using fast decay settings and low sustains will produce percussive instruments and even drums if the right sounds sources are used.

A faster ADSR envelope in the Korg

The faster envelope based patch plays back

The flexibility of the ADSR is well known and I equally at home controlling filters, effects, oscillator pitch and pretty much any parameter in your synth. Try using envelopes for adjusting parameters in other modulators to produce a more random and dynamic result over time.

In some more complex synthesisers you will come across envelopes with many more than the standard four points and this will allow you to create complex and evolving effects that unfold over time. Many of these more capable envelopes can even be synced with your DAW’s tempo.

Some synths such as Absynth have extremely complex envelopes


Step 3 - Low Frequency Oscillators

Another extremely common modulator is the LFO or Low Frequency Oscillator. This works in much the same way as the oscillators that produce sound in your synth. The main real difference is that an LFO produces no sound and is used purely as a modulation source.

The LFOs in Reason 6’s Subtractor

The movement (or oscillation) of an LFO can be routed to various destinations to create incredibly dynamic effects. Things like auto-pan, vibrato and tremolo are all essentially the results of LFO based modulation.

LFOs usually have a variety of waveforms and are capable of running at varying speeds. They will often work in a free and synced modes, allowing you to syncopate the results with the tempo your DAW is running at.

The various LFO wave shapes in Logic’s ES2

This sort of flexibility allows you to create anything from the simple vibrato effect I mentioned before to more complex set ups such as sample and hold or random filter effects.

Varying the speed of an LFO can also be a great performance based tool and is easily achieve by using an envelope to adjust LFOs rate over time. Alternatively the LFOs parameters can also be automated in your DAW. Using multiple modulators in this way is often the gateway to more unusual results.

The ES2 producing an auto pan effect using an LFO.


Step 4 - Steppers And Sequencers

A slightly rarer form of modulator is the stepper or step sequencer. Some advanced synths house these within their interface while selected DAWs actually offer this sort of module as a separate device that can be routed to an instrument.

Reason fro example includes a device called ‘The Matrix’. This is really a step sequencer but has a great ‘curve’ mode that can transform it into a step based modulation system. By hooking this device up to any of Reason’s instruments via the CV / Gate system, the Matrix can be used to creatively effects a huge list of parameters within the app.

The Matrix!

The Matrix producing a sample and hold type effect

Using a step sequencer to control instrument parameters is very different from working with more traditional modulators such as LFOs or envelopes. For one you get instant visual feedback on the adjustments you are making and the output is always perfectly locked to your project.

Some instruments actually features step sequencer, or stepper type modulators that are built right into their interface. Native Instrument’s Massive is a great example of this and not only features a stepper but a highly programmable perforce modulator. This allows the user to program different wave shapes for every step the modulator takes.


Step 5 - External And Performance Modulators

Not all modulators have to be modules within an instrument, sometimes the modulation effect can come from an external source. This could be a MIDI controller another instrument or even another piece of software via Rewire.

Most of the time the reason we use external modulators is to create a performance based effect. By this I mean the effect can be induced in real time whilst playing the instrument. These effects are often used in live or ‘performance’ situations.

One way of setting this up is to tell your synth to accept an input from say your mod wheel, aftertouch, velocity or a specific controller number. In many synths this can then be mapped directly to a parameter of your choice.

Mapping the mod wheel to the filter cut off in the Korg Polysix

This method will give you direct access to a specific parameter and is great for controlling effects depths, filter cut-off frequencies or even more extreme effects like distortion or frequency modulation.

There are alternatives to this very direct approach and we’ll take a look at these in the next step as we move into the territory of the Mod Matrix.


Step 6 - Routing And Mod Matrices

Although directly mapping your modulation sources to their destinations is a great way to control your instrument, much of the time you will want to induce more subtle effects such as vibrato, tremolo, auto-pan or even just a slight filter wobble.

All of these effects involve increasing the effect of a modulator that is already present and much of the time this will involve using a ‘via’ point. This basically means mapping your external controller (such as the mod-wheel) via your modulator, such as an LFO, before the LFO effects the actual parameter.

So to set up a simple vibrato that you can control via your mod-wheel, the wheel would be mapped to the oscillator’s pitch via a fast running LFO. When the mod wheel is then pushed the amount of LFO effecting the oscillator’s pitch would be increased.

This sort of set up may sound a little complex but once you get into the territory of the mod matrix it will suddenly become clear. Most synths have a modulation mapping system, the complexity of these systems can vary wildly but if you plan on performing a lot of routing then you should really opt for an instrument with a full blow Mod Matrix.

The Matrix is generally an open ended mapping system that allows you to map any source to any destination with an via point. Two great examples of systems like this are the ES2 synth in Logic Pro and the Thor Polysonic synth in Reason 6. Both of these instruments allow amazing freedom and flexibility when it comes to mod mapping.

The ES2’s Mod Matrix

Many other synths allow complex mapping and if you are serious about your synthesis and sound design you will really need to choose one that gives you this flexibility. If you find your current synth of choice is limited in this area, it may be time to move on!

A more complex modulation set up in Fabfilter’s Twin 2 synth


Step 7 - Automation As A Modulator

LFOs, Envelopes and external controllers are not the only source of modulation in modern music production systems. Automation is an incredibly powerful way to modulate just about any parameter in your mix.

Much of the time this data will be recording in real time and sometimes left unedited but even in this state it is still modulation and a perfectly valid way to control and change the sate of your instruments.

Once recorded your automation can actually be transformed into more uniform patterns that emulate traditional modulators if required. By using drawing tools, copy and paste and careful editing LFO like effects can be easily reproduced. So if you find an instrument lacking a specific modulator try building one yourself using your DAW’s automation system.

Hopefully this has cleared up the subject of modulators for you and given you a good idea of what the most common modulation sources actually do. No get stuck into your favourite synth and see what effects you can produce using it’s modulation system.

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