Subtractive Synthesis

An interactive tutorial on the fundamentals of sound design.

Subtractive synthesis is the most common approach in analog synthesizers. The idea is beautifully simple: start with a harmonically rich sound, then filter away frequencies to shape the tone.

Think of it like sculpting — you begin with a block of marble (a bright, harmonically dense waveform) and carve away the parts you don't want. The result can be anything from a soft pad to a screaming lead.

The signal flows left to right: an oscillator generates a raw tone, a filter shapes its harmonic content, and an amplifier controls its volume over time. Let's explore each module.

1. Oscillators — The Sound Source

The oscillator is the starting point of any synthesizer voice. It generates a raw waveform — a simple, repeating pattern that contains the raw harmonic material you'll shape with the rest of the synth.

Each waveform has a distinct character:

• Sine — The purest waveform. A single frequency with no harmonics. Smooth, flute-like, fundamental.
• Triangle — Contains odd harmonics that diminish quickly. Softer than saw, mildly buzzy.
• Saw (sawtooth) — Contains both odd and even harmonics. Bright, brassy, rich. The workhorse of subtractive synthesis.
• Square — Contains odd harmonics only. Hollow, woody, distinctive. Great for retro leads.

2. Filter — Tonal Sculpture

The filter is where subtractive synthesis earns its name. It removes frequencies from your raw oscillator signal, letting you transform a bright, buzzy sawtooth into a warm pad or a muffled bass.

The most common filter is the low-pass filter (LPF). It removes frequencies above a cutoff point while letting lower frequencies pass through. As you lower the cutoff, the sound becomes darker and more muted.

But there's more to a filter than just cutoff. Resonance (or "Q") emphasizes frequencies right at the cutoff point, creating a peak. High resonance gives a nasal, vocal quality; pushed further, it can approach feedback and self-oscillate into a pure tone.

Other filter types include:

• High-pass filter (HPF) — Removes lower frequencies, keeping highs. Great for creating thin, bright sounds or removing rumble.
• Band-pass filter (BPF) — Lets through a band of frequencies, rejecting both highs and lows. Useful for vocal-like effects.
• Notch filter — Removes a specific band of frequencies. Good for surgical corrections or unique effects.

3. Amplifier & Envelopes — Shaping Time

An oscillator running forever isn't very musical. Real sounds have shape — they begin, evolve, and end. The amplifier, controlled by an envelope, gives you this shape.

The standard envelope is ADSR:

• Attack — How long to reach full volume after a note starts. Fast attacks (10ms) are percussive; slow attacks (500ms+) are gradual swells.
• Decay — How long to fall from the initial peak to the sustain level.
• Sustain — The steady volume held while the note plays. Not a time, but a level.
• Release — How long to fade to silence after the note ends.

Attack and release are the most important for character. A plucky sound has fast attack and medium release. A pad has slow attack and slow release. A piano-like sound has fast attack and medium release.

4. LFO — Adding Movement

Static sounds aren't very interesting. Real instruments breathe, vibrate, and evolve. The Low-Frequency Oscillator (LFO) adds movement by modulating parameters over time.

An LFO is just an oscillator running at a very low frequency (typically 0.1–20 Hz) — too slow to hear as pitch, but perfect for creating rhythmic changes. You can route an LFO to:

• Pitch (vibrato) — Small pitch fluctuations create natural vibrato.
• Filter cutoff (filter sweeps) — The LFO modulates cutoff, creating wah-like effects.
• Amplitude (tremolo) — Volume fluctuations for classic tremolo.

The LFO has its own waveform, rate (speed), and depth (how much it affects the target).

5. The Complete Synthesizer

Now let's put it all together. A complete subtractive synthesizer combines oscillators, filters, amplifiers with envelopes, and LFOs into a single voice.

The LFO can modulate the oscillator (pitch), filter (cutoff), or amplifier (volume). The envelope shapes the amplifier's volume over time. The filter sculpts the oscillator's harmonics. Together, they create an infinite variety of sounds.

Preset Sounds

Try these presets to hear different synthesis techniques:

Next Steps

You've learned the core building blocks of subtractive synthesis. From here, explore:

• Multiple oscillators — Detuned oscillators create rich, detuned sounds.
• Filter envelope — Modulating cutoff with an envelope creates sweeping sounds.
• Modulation matrix — Route anything to anything for complex textures.
• Effects — Delay, reverb, and chorus add depth and space.

The beauty of synthesis is that these few components, combined creatively, can produce virtually any sound you can imagine. The synthesizer is a blank canvas — go paint.