Subtractive Synthesis Part 2: Advanced Voice Design

Multiple oscillators, filter envelopes, sub-bass, and more.

In Part 1, you learned the fundamentals: oscillators, filters, ADSR envelopes, and LFOs. That single-voice setup covers a lot of ground. But most synthesizers offer more — and those extra features open up entire categories of sounds.

This tutorial picks up where Part 1 left off. You'll learn to layer oscillators, shape filter cutoff over time, add sub-bass thickness, incorporate noise for texture, and make patches playable across the keyboard range.

1. Multiple Oscillators — Thickness and Character

A single oscillator can sound thin. Part of the appeal of analog synths is the slight detuning between oscillators — not perfectly in tune, but close enough to blend. This creates beating, shimmer, and a sense of width that's hard to get from one oscillator alone.

There are several common configurations:

• Detuned oscillators — Two oscillators at the same pitch, slightly detuned (5–15 cents). Creates unison thickness, the classic "supersaw" sound.
• Octave layering — One oscillator an octave down or up. The sub-oscillator concept (covered in section 3) is a specific case of this.
• Waveform mixing — Saw + square gives a hybrid character. Triangle + square adds subtle brightness without the harshness of saw.

When oscillators are detuned, you hear a slow beating — a periodic swelling in volume. The further apart they are in pitch, the faster the beating. At about 10–15 cents, the beating is musical rather than dissonant.

2. Filter Envelope — The Snap and Squelch

In Part 1, the envelope shaped the amplifier — how loud the note is over time. But we can also use an envelope to shape the filter cutoff. This is one of the most expressive tools in synthesis.

Here's what happens: when you play a note, the filter envelope moves the cutoff from a starting position to a peak, then to a sustain level, then releases when you let go. The cutoff is always there, but the envelope modulates it.

This creates sounds that start bright and decay to dark — like plucked strings. Or sounds that start muffled and open up — like brass swells. The key parameter is envelope depth: how much the envelope affects the cutoff.

3. Sub-Oscillator — Bass Weight

A sub-oscillator is one octave below the main oscillator, typically a sine or square wave. It's not meant to be heard distinctly — it's there to add weight and body to the low end.

The technique is simple: your main oscillator provides the character (saw for bite, square for hollowness), and the sub provides the thump. This is how you get those massive bass sounds in electronic music.

Why not just use another oscillator detuned down an octave? Sub-oscillators are often simpler — sometimes just a hard-sync'd square, sometimes silent (just for the fundamental). The point is predictable low-end reinforcement.

4. Noise Generator — Texture and Percussion

All the sources we've discussed so far are pitched — they produce a fundamental frequency and harmonics. Noise is different: it contains all frequencies equally, with no discernible pitch.

White noise sounds like static — bright and harsh. Pink noise has equal energy per octave, so it sounds more balanced and natural. In synthesis, noise is filtered to create texture:

• Kick drums — A sine wave with a fast pitch envelope, plus a noise burst for the beater attack.
• Snares — Mostly filtered noise, with a tuned sine or triangle for the body.
• Hi-hats — Band-pass filtered noise, often with a fast decay envelope.
• Breath sounds — Low-pass filtered noise mixed into pads for realism.

5. Keyboard Tracking — Consistent Brightness

When you play a sound across the keyboard, the filter cutoff stays fixed. But harmonics are relative to pitch — the 8th harmonic of a low note is much lower in Hz than the 8th harmonic of a high note.

This means a patch that sounds bright on low notes will sound increasingly dark as you play higher. The filter is cutting off more of the harmonic spectrum relative to the fundamental.

Keyboard tracking makes the filter cutoff follow the keyboard: as you play higher, the cutoff rises. This keeps the tone consistent across the range.

Typical values:

• 0% — No tracking. Same cutoff everywhere. Low notes bright, high notes dark.
• 100% — Full tracking. Each octave doubles the cutoff, matching the harmonic spread. Tone stays even.
• 50% — Half tracking. A compromise — slight brightness change, but not as drastic.

6. Portamento — Pitch Slides

Portamento (or glide) makes the pitch slide from one note to the next instead of jumping instantly. It's a staple of lead synths, TB-303 bass lines, and expressive playing.

There are two common modes:

• Always glide — Every note slides from the previous pitch.
• Legato only — Only slides when you play a note while holding another (overlapping notes).

The glide time controls how long the slide takes — from near-instant (10ms, barely perceptible) to very slow (500ms+), creating a pronounced swoop.

Putting It All Together

With these six techniques, you can design sophisticated synthesizer voices:

• Multiple oscillators give you thickness and harmonic complexity.
• Filter envelope adds dynamic shape to the tone, making plucks, brass swells, and evolving sounds.
• Sub-oscillator fills out the low end without muddying the mix.
• Noise generator adds texture, percussion, and breath.
• Keyboard tracking keeps patches consistent across the playable range.
• Portamento adds expression and that classic glide feel.

From here, the natural progression is effects (delay, reverb, chorus, distortion) and modulation routing (envelope to pitch, LFO to pulse width, velocity to filter). But these six tools are enough to create virtually any classic synth sound — and most modern ones too.

What's Next?

If you haven't worked through Part 1, start there. The fundamentals — oscillators, filters, ADSR, LFO — are prerequisite to what's covered here.

For deeper exploration:

• Effects — Delay, reverb, chorus, distortion transform raw sounds into finished productions.
• Modulation matrix — Route any source to any destination for complex, evolving textures.
• Polyphony — Managing multiple voices, glide in poly mode, CPU considerations.

The synthesizer is an instrument of infinite variation. These building blocks are just the beginning.