VCV Rack 2 — Building a Synthesiser That Doesn't Physically Exist
Imagine being given hundreds of electronic music modules and being told: build whatever instrument you want.
Not choose an instrument.
Not select a preset.
Build the instrument itself.
You decide what produces the sound. You decide what changes its pitch. You decide how long each note lasts, how bright it sounds, whether it moves around the stereo field and whether the next note is deliberately chosen or partly determined by chance.
You can even decide whether it needs a keyboard.
That is the wonderfully strange world of modular synthesis, and software such as VCV Rack 2 makes it possible to explore that world without filling an entire room with electronic equipment.
For me, this is one of the fascinating sides of creating music with computers. The computer is no longer simply pretending to be a piano, organ or conventional synthesiser.
It can become an electronic laboratory in which we construct instruments that may never have physically existed at all.
What Is a Modular Synthesiser?
Most electronic keyboards present themselves as finished instruments.
You switch them on, select a sound and play.
There may be enormous sophistication underneath, but the basic signal path has already been designed for you.
A modular synthesiser turns that idea around.
Instead of receiving a finished instrument, you receive the building blocks from which an instrument can be constructed.
Those building blocks might include:
oscillators;
filters;
amplifiers;
envelope generators;
low-frequency oscillators;
sequencers;
mixers;
effects;
clock generators;
random voltage generators;
logic modules;
control processors.
Initially, many of them do absolutely nothing.
That is an important point.
You can place an oscillator into an empty modular rack and it may be happily producing a waveform, but unless you connect it to something useful, you will hear nothing.
The instrument only begins to exist when we start making connections.
And that leads to perhaps the most interesting question in modular synthesis:
Why would I connect these two things together?
Starting With an Empty Rack
One of the best ways to understand VCV Rack is to start with almost nothing.
An empty rack can initially look rather intimidating.
Where are the sounds?
Where are the presets?
Where is the instrument?
The answer is:
We haven't built it yet.
So let us construct one.
Step 1 — We Need Something That Makes a Sound
Our first component can be an oscillator.
An oscillator repeatedly generates an electrical or mathematical waveform.
Common waveforms include:
sine;
triangle;
sawtooth;
square.
Each has a different harmonic structure and therefore a different sound.
A sine wave is comparatively pure.
A sawtooth contains many harmonics and can sound bright and buzzy.
A square wave has another distinctive harmonic structure.
Already we have choices.
But there is an immediate problem.
Connect the oscillator directly to the audio output and we may simply hear:
BEEEEEEEEEEP.
It does not stop.
That is because the oscillator does not necessarily know anything about musical notes. It is simply oscillating continuously.
We need to turn that raw electronic signal into an instrument.
Step 2 — Controlling the Loudness
We could next introduce a VCA — Voltage Controlled Amplifier.
Despite the name, in a synthesiser a VCA is commonly used to control the level of a signal.
Now we can potentially turn the oscillator up and down electronically.
But something has to tell the VCA when to become louder and quieter.
So we need another module.
Step 3 — Giving the Sound a Shape
Enter the envelope generator.
A common envelope uses four stages:
Attack — Decay — Sustain — Release
Often abbreviated to ADSR.
Imagine pressing a key.
Attack
How quickly does the sound reach its initial maximum level?
A percussive sound may have an extremely fast attack.
A slowly swelling string-like sound may have a much longer one.
Decay
After reaching its initial peak, how quickly does the sound fall towards its sustained level?
Sustain
What level does the sound remain at while the note continues?
Release
What happens when the note ends?
Does the sound disappear instantly?
Or does it fade away gradually?
This is where modular synthesis starts becoming particularly interesting.
The oscillator creates the sound.
The VCA controls its level.
The envelope controls the VCA.
One module is controlling another.
We are no longer merely generating sound.
We are constructing behaviour.
Step 4 — Now Give It Some Pitch
Next we need a way of deciding which notes the oscillator should play.
A conventional keyboard is one possibility.
But modular synthesis does not insist that music must start with somebody pressing a key.
We could use a sequencer instead.
Imagine programming eight notes:
C - E - G - A - G - E - D - C
The sequencer can repeatedly send control information telling the oscillator which pitch to produce.
We now need some timing information as well.
So we introduce a clock.
The clock advances the sequencer.
The sequencer controls the oscillator.
The oscillator produces the waveform.
An envelope shapes each note.
The envelope controls the VCA.
The VCA feeds the audio output.
Our empty rack has become a musical instrument.
But we have barely started.
Step 5 — Making the Sound More Interesting With a Filter
Suppose our sawtooth oscillator sounds rather harsh.
We can pass it through a filter.
One common example is a low-pass filter.
Very broadly, this allows lower frequencies through while progressively reducing frequencies above its cutoff region.
Turn the cutoff down and our bright sawtooth becomes darker and softer.
Turn it up and more of the harmonics return.
That is useful.
But turning a knob by hand is not the only option.
What if something else turned the knob for us?
This is where the idea of control voltage becomes central to modular synthesis.
Control Voltage — The Language Between Modules
In a physical modular synthesiser, voltages can be used to control parameters.
One voltage might determine pitch.
Another might control volume.
Another might change filter cutoff.
Another could alter the speed of an effect.
VCV Rack recreates this concept in software.
This means that instead of thinking:
"I will adjust the filter."
we can start asking:
"What else could adjust the filter for me?"
That question opens an enormous creative world.
Enter the LFO
An LFO — Low Frequency Oscillator — is another oscillator, but it normally operates much more slowly than an audio oscillator.
Rather than hearing its oscillation directly, we can use it to control something else.
Connect an LFO to filter cutoff and the filter can automatically open and close.
Connect it to pitch and we can create vibrato.
Connect it to amplitude and we can create tremolo.
Connect it to stereo position and the sound can move from side to side.
And there is nothing stopping us from using several LFOs.
One might slowly alter the filter.
Another could control pulse width.
Another could alter the speed of the first LFO.
Now things are becoming considerably more complicated.
And much more interesting.
What Happens If One Control Controls Another Control?
This is where modular synthesis begins moving beyond the architecture of many conventional instruments.
Suppose LFO 1 controls the filter.
Instead of running LFO 1 at a constant speed, LFO 2 could alter the frequency of LFO 1.
The filter movement itself now speeds up and slows down.
We could then use an envelope to control the depth of that modulation.
Or a sequencer could select different modulation amounts for different steps.
Or a random voltage could occasionally change something.
The possibilities multiply extremely quickly.
A modular synthesiser therefore encourages a different style of thinking.
Rather than asking:
"Which sound shall I select?"
we ask:
"What process shall I construct?"
The Wonderful World of Randomness
Random generators are particularly fascinating.
At first, randomness may seem to be the opposite of composing music.
Surely we want control?
But randomness does not have to mean complete chaos.
Imagine a sequence in which seven notes are deliberately programmed, but every eighth note is selected randomly from a restricted range.
Or imagine a filter whose cutoff changes very slightly and unpredictably with every note.
Or a percussion pattern in which there is a 20% chance that an additional sound will occur.
Now the music can become slightly different every time it plays.
We can decide how much uncertainty we permit.
That creates an intriguing relationship between composition and probability.
The composer designs the rules.
The synthesiser explores the possibilities permitted by those rules.
A Practical Experiment — Build a Generative Instrument
This would make an excellent VCV Rack experiment.
Start with:
one oscillator;
one sequencer;
one envelope;
one VCA;
one filter;
one clock;
one audio output.
Get the basic sequence working.
Then add an LFO controlling the filter.
Next, introduce a random voltage generator.
Use the random voltage very gently.
Perhaps it changes the filter cutoff.
Perhaps it occasionally changes the duration of a note.
Perhaps it changes which step the sequencer moves to.
Then add delay or reverb.
Listen for a few minutes.
The fascinating question is:
Have we written a piece of music, or have we built a machine that writes variations of a piece of music?
That is a much more interesting question than simply asking what a particular synthesiser module does.
Effects Become Part of the Instrument
Effects such as delay and reverb are often considered the final stage of music production.
Record the instrument first.
Add effects afterwards.
A modular environment does not force us to think that way.
A delay can become part of the instrument itself.
Its delay time could be modulated.
Its feedback could change automatically.
A signal could be split so that the original sound travels down one path while another version travels through several effects.
Those signals could later be recombined.
We can even feed signals back into earlier parts of the system.
Feedback needs careful control, but creatively it can produce fascinating results.
The distinction between instrument, effect and composition begins to blur.
Why VCV Rack Can Become Enormous
A physical modular synthesiser has an obvious limitation.
Every additional module costs money.
It occupies physical space.
It needs power.
It needs another patch cable.
Sooner or later, the rack is full.
A virtual rack changes those limitations dramatically.
VCV Rack has access to a large ecosystem of modules, and the range of possibilities can become almost absurd.
There are modules for traditional synthesis functions, but also modules involving:
probability;
logic;
switching;
sequencing;
clock division;
mathematical functions;
sample manipulation;
spectral processing;
MIDI;
recording;
mixing;
visualisation;
unusual modulation;
experimental sound generation.
A virtual modular rack could become far larger than anything I could realistically accommodate as physical hardware.
That does not necessarily mean bigger is better.
In fact, one of the most useful exercises may be to impose restrictions.
Try Building a Synthesiser With Only Ten Modules
This is a challenge I particularly like.
Give yourself a maximum of ten modules.
Now build something musically interesting.
Suddenly every module has to earn its place.
Do I really need another oscillator?
Could one LFO control several destinations?
Could the sequencer perform two jobs?
Could one envelope control both amplitude and filter movement?
Restrictions often encourage creativity.
It is rather like photography.
Owning twenty lenses does not automatically produce better photographs.
Sometimes going out with one camera and one lens forces you to think much harder about the picture.
Modular synthesis can be similar.
Patch Cables Are Ideas
The visual appearance of VCV Rack is part of its appeal.
As the patch develops, virtual cables begin crossing the screen.
Initially there may be three or four.
Later there might be twenty.
Eventually the screen can look like a plate of multicoloured electronic spaghetti.
But every cable represents an idea.
This controls that.
This triggers that.
This signal is being sent there.
This output is affecting this parameter.
That makes modular synthesis unusually visual.
You can often understand something about how an instrument works simply by tracing its connections.
A Brilliant Way to Learn About Sound
This is also why I think software such as VCV Rack has considerable educational value.
Concepts that can initially appear abstract become practical.
Want to understand frequency?
Listen to an oscillator while changing it.
Want to understand harmonics?
Compare sine, triangle, square and sawtooth waves.
Want to understand filters?
Look at and listen to what happens when high-frequency components are removed.
Want to understand amplitude envelopes?
Change attack and release times dramatically.
Want to understand modulation?
Connect an LFO and hear the result.
Want to understand frequency modulation?
Use one oscillator to alter another.
Suddenly ideas from physics, mathematics, electronics, computing and music begin meeting in the same place.
That is precisely the kind of crossover I find particularly interesting.
Music, Physics, Mathematics and Computing Meet
A synthesiser is an excellent example of subjects refusing to stay in their traditional boxes.
There is physics in oscillation and sound waves.
There is mathematics in periodic functions, harmonics and signal processing.
There is electronics in the concepts inherited from physical synthesisers.
There is computing in the software implementation.
There is psychology in our perception of pitch, rhythm, timbre and loudness.
And ultimately there is music.
The technical knowledge is not the final objective.
The final question is whether the result sounds interesting.
From Experiment to Music Production
VCV Rack does not have to remain an isolated experiment.
Sounds and sequences created through modular synthesis can become part of a much larger music-production workflow.
A modular patch might provide:
an evolving background texture;
an unusual bass line;
rhythmic percussion;
sound effects;
an ambient atmosphere;
a strange transition;
a repeating sequence;
a cinematic drone;
an entirely new electronic instrument.
That material can then become part of a larger project inside a DAW.
This is where the possibilities become especially relevant to my own interests in music, video and film production.
Instead of searching through a library for precisely the sound I want, I can potentially ask a different question:
Could I build it?
Designing Sounds for Film and Video
Imagine I need a sound for a science-fiction video.
I could search through presets until I find something suitable.
But modular synthesis offers another route.
Perhaps I start with two oscillators slightly detuned from one another.
I slowly modulate their pitch.
I pass them through a filter whose cutoff changes almost imperceptibly.
I add some random movement.
I send the result through a large reverb and a slowly changing delay.
Now I have not merely selected "Sci-Fi Atmosphere 27".
I have designed a sound specifically for the project.
For another film I might need mechanical tension.
A clock, several sequencers, noise sources and carefully controlled random triggers might create something completely different.
That is where synthesis becomes sound design.
You Do Not Have to Understand Everything Before Starting
The enormous choice of modules can make modular synthesis appear intimidating.
My approach is the same one I use with many technical subjects:
start with something that works, then change one thing.
Build one oscillator.
Make it audible.
Add an envelope.
Add a filter.
Add a sequencer.
Then experiment.
What happens if this cable goes there?
What happens if the LFO is much slower?
What happens if the envelope controls the filter as well as the amplifier?
What happens if the sequence has five steps rather than eight?
What happens if a random generator controls the timing?
Some experiments will sound dreadful.
That is perfectly useful.
You have discovered something.
Others will produce results you would never have deliberately programmed.
Those unexpected discoveries are one of the pleasures of modular synthesis.
Save the Patch — Because You May Never Recreate It
There is another lesson worth learning.
Save interesting patches.
When a modular system becomes sufficiently complicated, recreating exactly the same configuration may be surprisingly difficult.
A tiny adjustment can transform the result.
That is particularly true when randomness, feedback and multiple interacting modulation sources are involved.
The patch itself becomes part of the composition.
In effect, you have designed a new instrument.
The Bigger Idea — Stop Thinking About Presets
Perhaps the most important thing VCV Rack teaches is not how to operate a synthesiser.
It teaches a different way of thinking.
A conventional instrument encourages the question:
"What can this instrument do?"
A modular system asks:
"What instrument would I like to exist?"
That is a much bigger question.
And because the instrument is software, we can experiment with ideas that would be difficult, expensive or simply impractical to construct physically.
Hundreds of modules.
Dozens of connections.
Sequencers controlling sequencers.
Randomness controlling modulation.
Envelopes altering effects.
Oscillators controlling other oscillators.
A patch can be tiny and elegant or enormous and wonderfully ridiculous.
There is no requirement that anybody has built the instrument before.
Conclusion — Build the Instrument First, Then Play It
Modern music technology gives us access to extraordinary libraries of instruments and sounds.
Sometimes, however, the most interesting sound is the one that is not already in the library.
VCV Rack 2 gives us something different.
It gives us the components.
An oscillator does one job.
A filter does another.
An envelope does another.
A sequencer does another.
Individually, they may seem quite simple.
The magic appears in the connections.
And that is why the most interesting question in modular synthesis is rarely:
"What does this module do?"
It is:
"What would happen if I connected it to that?"
Then you make the connection.
Sometimes you get silence.
Sometimes you get noise.
Sometimes you get something awful.
And occasionally you hear something and think:
I have never heard an instrument do that before.
Perhaps that is because, until a few seconds ago, that instrument didn't exist.
Practical Challenge
Open VCV Rack 2 with an empty rack and set yourself one rule:
Do not load a finished synthesiser patch.
Start with a single oscillator and build an instrument one module at a time.
For every new module, ask:
What job do I want this module to perform?
Then ask the more interesting question:
What else could it control?
That second question is where modular synthesis really begins.
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