MODULATION PRIMER
Get up to speed with an in-depth look at how to make your sounds move, as we explain the basic building blocks and tools you’ll need
LFO
Just like a synth’s oscillator, the LFO has several shapes to choose from, only there’s one big difference: it operates very slowly. Attach an LFO to a sound’s level, and you’ll hear the level ‘wobble’ up and down – just as if you were tweaking the parameter yourself, only now it’s being done automatically by this ‘low frequency oscillator’.
The LFO’s Rate (or speed, or frequency) can usually be locked to your DAW’s tempo or set in Hz (cycles per second). It’s Depth controls how far it moves the parameter you’ve assigned it to. Interesting LFO shapes include stepped waves, and the ‘random’ sample-and-hold. Some LFOs can get so fast that they become audible oscillators by introducing sideband harmonics.
Common things to hook an LFO to include filter frequency, filter resonance, wavetable position or panning. Once you’ve mastered the basics, try modulating one LFO’s rate with another LFO for interesting speed changes.
Some synths have LFO attack or ‘fade-in’ controls, making their effect kick in slowly over time. A common example is delaying vibrato, so pitch wobbling creeps in as a note is held.
ENVELOPE
Like an LFO, an envelope controls the value of whatever you connect it to, but instead of being ‘always on’, it’s triggered every time a note is played. The most common example is a synth’s amplitude, which rises when a key is pressed, then falls when the key is released.
A typical envelope has four stages: an Attack stage, where the level rises after the note is pressed; a Decay stage, where the level reduces a little; a Sustain stage, which keeps the level at a value of your choosing until you let go of the key. At that point, the final Release stage kicks in, fading the level down again for a duration of your choosing. This typical envelope type is therefore often called an ADSR envelope.
A common modulation target for an envelope is filter cutoff, but try hooking one up to any parameter of your choosing for more inspiring effects.
In many modern synths and samplers, envelopesp can be looped,p , making g them something between an envelope and an LFO. Other designs allow you to invert the signal, starting at full level and fading down when a note is struck. Some envelopes have more stages, than the traditional ADSR, adding Hold or Delay stages into the design.
BREAKPOINT MODULATOR
Popularised by NI Massive, and taken further by cutting-edge instruments like Vengeance-Sound Avenger and Xfer Serum, many modern synths allow you to draw your own custom modulation shapes. Add, remove and reposition nodes where you want them, then move and bend the resulting lines and curves to precisely define the shape of your bespoke modulation signal.
By telling this modulator to loop round and round indefinitely, it takes on the role of a cyclical LFO. Switch it into ‘one-shot’ mode, and the modulation will only happen once when a note is pressed, making it behave more like a traditional envelope.
SEQUENCER
Synonymous with classic drum machines and old-school modular rigs, a sequencer is a gridbased module that outputs regimented control data. Draw in different values across the steps, set the sequencer’s Rate (either synced to host tempo, or free-running in Hz), then use its output to trigger other parameters.
One classic example is Reason’s Matrix Sequencer, which can be hooked up as a CV controller to any parameter in Reason’s rack – including third-party VST plugin parameters since Reason 9.5. Programming a sequence of voltages into the Matrix means that you can run any effect in a rhythmic way, whether that’s turning it on and off on different steps, or varying the levels of parameters across the sequence.
Often confused with step sequencers, arpeggiators traditionally take in the multiple notes of a chord, and divide these notes up into a regimented monophonic sequence at a direction (up, down, up-and-down, etc) and speed defined by the user. However, most modern synths also allow you to hook them up to control other parameters, too.
MIDI MODULATORS
The forward-thinking folks who came up with the MIDI specification had modulation in mind, keeping plenty of messages free for non-notebased operation. Your virtual instrument might listen to MIDI messages like Modulation, Mod Wheel, Expression and Aftertouch commands, and some might even be able to use certain MIDI message inputs of modulators for its parameters – routings like this are often accessed via a mod matrix.
The most-used MIDI property is Velocity. It’s usually hardwired to determine notes’ levels and filter cutoff frequencies, but velocity can often be routed to other parameters, depending on the software you’re using. It’s not a separate MIDI message in itself – it comes back in with Note On and Note Off message – but this goes to show you the power that’s available from under a byte of data.
With the power of computer-based music production, we can now draw and record continuous messages like these right alongside our piano roll, too.
SIDECHAIN
A sidechain (or ‘key input’) is a classic way of modulating a compressor, making its gain reduction circuit trigger from another track, not the track that the compressor is placed over. This means you could insert a compressor over a pad channel, and trigger gain reduction of the pad using a rhythmic signal such as a kick. This is often called ‘ducking’ or ‘sidechaining’, and a similar philosophy involves using a gate instead of a compressor, but there are other ways to get some sidechain action into a mix.
Sidechain EQ uses one signal (the sidechain) to determine the EQ settings on another signal (the main track). One use is to give your main signal the frequency profile of the sidechain audio, while another us is to do the opposite, taking the frequencies present in the sidechain away from the main sigal – useful in mixing, as you can imagine.
The salient difference is that, by sidechaining, you’re using an audio signal as a trigger, so when you change the level, duration or content of that audio signal – or replace it with a different audio signal entirely – the modulation will change with it. A common example is the use of a short, silent ‘ghost’ click to trigger 4/4 ducking.
ENVELOPE FOLLOWER
When we set an envelope to control a sound’s amplitude over time, we’re defining the sound’s dynamic response. What if we take the changing level of an input sound and use it to dictate the movement of parameters?
Envelope followers do just that, and the perfect example is the auto-filter (or ‘auto-wah’), which detects the amplitude of the input sound, and uses this trigger signal to modulate the cutoff frequency of a filter. As the input jumps in level, the filter responds and opens up more, and vice versa.
Envelope follower modules usually feature a Gain parameter, which you use to set the strength of the modulation; Rise and Fall controls, which define the onset and offset of modulation; and some kind of display, so you can visualise the input signal’s waveform in real time as you adjust settings.