Oscillators and Waveforms

What Is an Oscillator?

An oscillator is the noisemaker — the thing that produces the sound. It’s an electronic circuit (or a digital algorithm) that generates a repeating waveform. It vibrates at a specific frequency, just like a guitar string — except instead of moving air directly, it generates an electrical signal that eventually becomes sound through a speaker. Every synthesizer starts here: a basic beep or boop, a raw signal waiting to be shaped.

The waveform is the shape of that vibration. Different shapes produce different recipes of harmonics, and different harmonic recipes give you different timbres. Choose your waveform and you’ve chosen your starting ingredients.

The Waveforms

There are five waveforms you’ll encounter on virtually every synthesizer ever made. Each one has a distinct harmonic fingerprint:

Sine Wave

The simplest possible sound. One frequency. No harmonics, no overtones — just the fundamental, pure and clean. It sounds smooth, round, and frankly a bit boring on its own. But sine waves are the building blocks of every other waveform. Mathematically, any complex waveform can be broken down into a stack of sine waves at different frequencies and amplitudes. That’s not just a neat fact — it’s the entire theoretical foundation of audio engineering.

A sine wave through a filter sounds exactly like a sine wave. There are no harmonics to remove. So while it’s useful as a building block and for sub-bass, it’s not much of a starting point for subtractive synthesis.

Sawtooth Wave

The party waveform. A sawtooth contains all the harmonics — odd and even — and they taper off gradually as they go up. That’s why it sounds so rich, so buzzy, so full of energy. If you only load one waveform into a synth, make it this one. It gives you the most to work with when you start filtering.

You can build a sawtooth by stacking sine waves: the fundamental at 100 Hz, plus 200 Hz at half the amplitude, plus 300 Hz at a third, plus 400 Hz at a quarter, and on up. Each new harmonic adds more brightness and texture. It’s like a mullet — business in the front, party in the back.

Square Wave

Hollow and woody. A square wave contains only the odd harmonics — the 1st, 3rd, 5th, 7th, and so on. The even harmonics are completely absent. That’s what gives it its distinctive “hollow” quality — think clarinet, or a classic 8-bit video game tone.

A variant of the square wave is the pulse wave, where instead of spending equal time at the top and bottom, the wave spends more time in one position than the other. The ratio is called the pulse width, and changing it (pulse width modulation, or PWM) dramatically alters the harmonic content. We’ll come back to this in Chapter 5.

Triangle Wave

Somewhere between a sine and a square. A triangle wave has only odd harmonics like a square wave, but they taper off much faster — the 3rd harmonic is nine times quieter than the fundamental, the 5th is twenty-five times quieter. The result is soft, mellow, almost flute-like. Useful for gentle pads and bass sounds where you want a little more character than a sine but less aggression than a saw.

Noise

Not a pitched waveform at all. White noise is random frequencies at random amplitudes, all at once — every frequency in the audible spectrum, equally represented. It has no pitch, no harmonics, no musical quality. But it’s incredibly useful: the “air” in a synth pad, the body of a snare drum, the texture of wind and ocean sounds. In synthesis, noise is often mixed in small amounts with a pitched oscillator to add grit and realism. (There’s more to the world of noise than white — see the noise colors article for the full picture.)

Putting It Together

The key insight from all of this: waveforms with more harmonics give you more to work with when you start filtering.

A sine wave through a low-pass filter sounds like a sine wave. There’s nothing to remove. A sawtooth wave through the same filter can sound like a hundred different things, depending on where you set the cutoff. That’s why “start rich, subtract to taste” is the fundamental principle of subtractive synthesis — and why the sawtooth is the default starting point for most sound design.

Distortion and Saturation: Harmonic Addition

One more concept before we move on. Distortion is, fundamentally, the addition of harmonics. When a signal clips — exceeds the maximum capacity of whatever’s processing it — new frequencies are created that weren’t in the original signal.

Imagine driving on a highway. A sine wave is smooth steering — gentle curves, no sharp edges. Now turn up that sine wave until it clips. The tops and bottoms of the wave get squared off — sharp edges where the curve used to be. Those sharp edges are high-frequency content. The sharper the edge, the higher the frequencies. Turn up a sine wave hard enough and it becomes a square wave — you’ve just synthesized a whole set of harmonics that weren’t there before by overdriving the signal.

Soft clipping (what we call saturation or “warmth”) rounds those edges slightly — it adds mostly low-order harmonics (the 2nd and 3rd). These are musically related to the original signal, which is why saturation sounds “warm” and “pleasant.” It’s the sound of analog tape, tube preamps, and overdriven guitar amps.

Hard clipping creates sharper edges and adds higher-order harmonics and intermodulation products — frequencies that aren’t as musically consonant. This is “distortion” in the aggressive, crunchy sense. Useful as an effect, but not something you want happening accidentally. (The Distortion video walks through this visually — watch a sine wave clip into a square wave in real time.)

Every sound has a harmonic fingerprint. Distortion and saturation change that fingerprint by adding harmonics that weren’t there before. It’s the opposite of subtractive filtering — instead of removing harmonics, you’re creating new ones.

Key Tracking

When you press a key on a keyboard, the oscillator changes its frequency to match the note you played. That’s key tracking — the pitch follows the keyboard.

It sounds obvious for oscillators — of course higher keys produce higher notes. But here’s why it matters: filters can also track the keyboard. When key tracking is on for the filter, the filter cutoff moves up when you play higher notes and down when you play lower notes — the filter follows the keyboard, keeping the same relative brightness across the range. Turn key tracking off and the filter stays at one fixed cutoff — low notes sound bright (lots of harmonics above the cutoff) while high notes sound dull (their fundamentals may be near or above the cutoff). We’ll explore this in the next chapter.

The Signal Flow

The big picture of subtractive synthesis, in one line:

Oscillator → Filter → Amplifier

The oscillator generates the raw waveform. The filter shapes its harmonic content. The amplifier controls its volume. That’s the whole architecture. Everything else — envelopes, LFOs, modulation routing — is about controlling how those three stages behave over time.

We covered the filter last chapter. The oscillator is this chapter. Next, we’ll add envelopes and amplifiers — the parts that make the sound move.

What to Listen For

• Load a sawtooth wave in any synth and play a note. Now switch to a square wave at the same pitch. Hear the difference? That’s the harmonic content changing — odd + even harmonics vs odd only.
• Sweep a low-pass filter across a sawtooth wave. Listen to how many different sounds live inside that one waveform, depending on where you set the cutoff.
• Listen to a real instrument — a cello, a trumpet, an electric guitar — and try to guess which basic waveform it’s closest to. A bowed cello string is surprisingly close to a sawtooth. A clarinet is close to a square wave. A flute is close to a sine. These aren’t perfect matches, but the analogy helps build intuition.