What Is Synthesis?

Sound Is Vibration

Put your hand on a speaker cone while music plays. You feel it moving — pushing out, pulling back, pushing out again. That back-and-forth motion pushes air molecules together, then lets them spread apart, creating alternating zones of high and low pressure that radiate outward from the speaker like ripples in water. When those pressure waves reach your ear, your eardrum vibrates in sympathy. Your brain interprets that vibration as sound.

The speed of that vibration determines the pitch you hear. A slow vibration — say, 80 cycles per second — sounds low. A bass note. A fast vibration at 4,000 cycles per second sounds high and piercing. The human ear can detect vibrations roughly between 20 Hz and 20,000 Hz, though the upper range shrinks with age and exposure.

The shape of the vibration — its waveform — determines the tone color, or timbre. A perfectly smooth, rounded vibration produces a pure tone with no character: a sine wave. A jagged, angular vibration produces something bright and buzzy. The same pitch can sound like a flute or a chainsaw depending on the shape of the wave. That shape is what synthesis manipulates.

The Harmonic Series

Play a single note on a piano. You hear one pitch, but what’s actually happening is more complex. The string vibrates at its full length — that’s the fundamental frequency, the pitch you’d name if someone asked “what note is that?” But the string is also vibrating in halves, thirds, quarters, fifths, and so on, all at the same time. Each of those partial vibrations produces its own frequency, and those frequencies stack on top of the fundamental.

If the fundamental is 100 Hz, the harmonics fall at 200 Hz, 300 Hz, 400 Hz, 500 Hz, and upward in a predictable series. The second harmonic (200 Hz) is an octave above the fundamental. The third (300 Hz) is an octave and a fifth. The fourth (400 Hz) is two octaves. The fifth harmonic (500 Hz) is two octaves and a major third. This isn’t arbitrary — it comes from the physics of vibration. Every acoustic instrument obeys the same series.

What makes a trumpet sound different from a clarinet, even when they play the same note, is the relative loudness of each harmonic. A trumpet has strong upper harmonics — lots of energy at the 5th, 6th, 7th multiples and beyond. A clarinet emphasizes odd-numbered harmonics (1st, 3rd, 5th, 7th) because of its cylindrical bore. A flute is almost all fundamental with very little harmonic content, which is why it sounds “pure.”

This matters for synthesis because every waveform you’ll work with is just a recipe of harmonics. A sawtooth wave contains all harmonics in a specific pattern. A square wave contains only the odd harmonics. A sine wave contains no harmonics at all — just the fundamental. Understanding the harmonic series is understanding what you’re actually sculpting when you turn knobs on a synthesizer.

Why Synthesis Matters

You might wonder why any of this matters if you can just load a preset. And presets are fine — nobody’s arguing against using them. But a preset is someone else’s answer to a question you may not have been asking. When you understand synthesis, you can start from a sound in your head and build toward it. You can take a preset that’s 80% right and fix the 20% that’s wrong. You can hear a texture in a recording and reverse-engineer how it was made.

A good exercise: identify your “desert island synth” — the one instrument you’d take if you could only have one. The answers vary wildly (hardware Moogs, software wavetable synths, plugins that emulate machines from the 1980s), but the exercise surfaces something consistent: the people who know synthesis don’t just use their synth. They own it. They understand why it does what it does, and that understanding is what lets them shape sound with intention rather than luck.

There’s a practical angle too. Every DAW ships with synthesizers. Every plugin bundle includes them. If you produce any kind of electronic or electronic-adjacent music, synthesis is the raw material of your palette. Drums, basses, pads, leads, textures, effects — all of it comes down to generating waveforms and processing them. The more you understand about what’s happening under the hood, the faster you work and the more distinctive your sounds become.

A Brief History: From Telharmonium to VCV Rack

The idea of generating musical tones with electricity is older than most people think. Thaddeus Cahill built the Telharmonium in 1897 — a 200-ton machine that generated tones using spinning electromagnetic wheels and transmitted them over telephone lines. It was additive synthesis, technically. Each wheel produced a sine tone at a specific harmonic, and combining wheels at different volumes produced different timbres. The concept was sound. The execution weighed seven railroad cars.

The next fifty years produced a series of increasingly practical electronic instruments. The Theremin (1920s), the Ondes Martenot (1928), the Hammond organ (1935) — all exploring different ways to generate and control electronic sound. But the modern synthesizer, the thing most people picture when they hear the word, traces back to the 1960s.

Robert Moog and Don Buchla, working independently on opposite coasts, both built modular synthesizers that used voltage control. Moog’s approach (East Coast synthesis) emphasized a keyboard interface, subtractive filtering, and familiar musical structures. Buchla’s approach (West Coast) emphasized touch plates, wavefolding, and more experimental tonal territory. Both were modular: separate function blocks connected by patch cables, with each module’s behavior controlled by voltage signals from other modules.

From there, the timeline compresses. The Minimoog (1970) put a synthesizer in a portable box with a fixed signal path — no patch cables. Yamaha’s DX7 (1983) brought digital FM synthesis to the mass market. Samplers, wavetable synths, virtual analog, granular engines, physical modeling — each decade added new methods, but every one of them still reduces to the same underlying operations: generate a waveform, shape its spectrum, control its amplitude, and modulate the whole thing over time.

Setting Up VCV Rack

This guide uses VCV Rack as its primary teaching tool. There’s a reason for that: VCV Rack is free, it runs on Mac, Windows, and Linux, and it’s a virtual modular synthesizer — meaning every connection between modules is a visible cable that you patch yourself. Nothing is hidden inside a closed interface. When you connect an envelope generator’s output to a VCA’s control input, you see the cable. When you route an LFO to a filter’s cutoff, you see that cable too. The signal flow is always visible, which makes it a better learning environment than a plugin where everything happens behind a panel.

To install:

1. Go to vcvrack.com↗ and download VCV Rack 2 (the free version).
2. Install it like any other application. On Mac, drag it to Applications. On Windows, run the installer.
3. Open it. You’ll see an empty rack — a virtual Eurorack case with nothing in it.
4. Right-click anywhere on the rack to open the module browser. This is where you’ll find every module available to you.

For this guide, you’ll mostly use the built-in “Fundamental” modules that ship with VCV Rack. These are the basics: oscillators (VCO-1, VCO-2), a mixer, a VCA, an envelope generator (ADSR), an LFO, a filter (VCF), and an audio output module. Start by adding an audio output module (Audio > Audio-2 or Audio-8) and make sure it’s routed to your speakers or headphones. If you don’t hear anything yet, that’s expected — you haven’t built a voice.

In the next chapter, we build one.

What to Practice

• Install VCV Rack and get audio output working. Add an Audio-2 module, select your audio device, and confirm you can hear sound when you patch something to it (even just connecting a VCO directly to the output to test).
• Explore the module browser. Right-click the rack and scroll through the available modules. Don’t try to learn them all — just get a sense of what’s there. Notice the categories: oscillators, filters, envelopes, LFOs, mixers, effects, utilities.
• Listen to a sine wave. Add a VCO-1, patch its SIN output to your audio module, and sit with it. Then switch to the SAW output. Then TRI. Then SQR. Don’t worry about what these names mean yet — that’s the next chapter. Just notice that each one sounds different even though the pitch is the same.
• Read about the harmonic series. The SynthSecrets series (available free online from Sound on Sound) covers this in depth. So does any acoustics textbook — and the Music Theory guide covers the physics of sound from a different angle. The more intuitive your understanding of harmonics, the easier everything else in this guide becomes.