Staring at a synth full of knobs and unsure where to start? Subtractive synthesis is simple: begin with a bright, harmonically rich waveform, then use a filter and envelopes to carve away what you don’t want.
This guide is part of our wider look at sound design.
| Item | Value |
|---|---|
| Signal flow | Oscillators, mixer, filter, then envelope generator |
| Richest basic wave | Sawtooth: both even and odd harmonics |
| Square wave | Odd harmonics only |
| Main filter controls | Cutoff and resonance |
| Low pass filter | Cuts all sound above the cutoff frequency |
Figures come from FabFilter’s subtractive synthesis basics and Apple’s Logic Pro guide. Documentation can change, so check the sources before you rely on them.
What subtractive synthesis actually does
Apple’s Logic Pro guide explains the idea with a sculptor’s story, and sums it up as: “You filter (cut away) the parts of the sound that you don’t want to hear.” The result is a sound shaped by removal rather than built up piece by piece.
The approach assumes an instrument can be approximated with a simple oscillator. The oscillator’s signal then goes to a filter, which stands in for the losses and resonances in the body of a real instrument.
Most classic analog-style synths, and many software instruments that copy them, work this way. Once you learn the layout on one, the same logic carries over to nearly all of them.
The signal path, step by step
FabFilter lists the flow in order. Following it left to right is the easiest way to read any subtractive synth’s panel.
- Sound is generated using one or more oscillators.
- The signals from these oscillators are combined using a mixer.
- The combined sound passes through a filter section, which affects the spectrum.
- The filtered sound passes through an amplifier controlled by an envelope generator, which shapes its amplitude over time.” Change the table’s final stage to “envelope-controlled amplifier.
Put simply, the oscillator decides the raw tone, the filter decides the brightness, and the envelope decides how the loudness moves over time. Any problem you hear can usually be traced to one of those stages.
Oscillators: choosing your raw material
Because you can only remove what is already there, the waveform matters a great deal. A typical oscillator offers sawtooth, square, triangle, sine and noise.
- Sine: the purest basic wave shape, with no harmonic overtones.
- Triangle: a soft, warm tone, with odd harmonics at lower amplitudes.
- Square: a more metallic sound containing odd harmonics at a relatively high amplitude.
- Sawtooth: the richest of the basic waves, with both even and odd harmonics at a relatively high amplitude.
- Noise: white and pink noise are useful for breath, hiss and percussion.
A sine wave gives a filter almost nothing to work with. A sawtooth gives it plenty, which is why saw waves are the usual start for basses, leads and pads.
Many synths offer more than one oscillator. Layering two slightly detuned saws is a classic way to thicken a sound before the filter even starts.
Filters: where the shaping happens
Apple identifies cutoff and resonance as the main filter controls on most subtractive synths. These two knobs do most of the tonal work.
Cutoff
A low pass filter progressively attenuates frequencies above its cutoff. Lowering the cutoff on a saw wave removes upper harmonics, turning a buzzy tone into a dull, rounded one.
Resonance
The resonance control emphasizes or suppresses signals around the cutoff frequency. Turn it up and the area near the cutoff gets a pronounced peak, which gives the classic “wow” or squelch as you sweep the cutoff.
At extreme settings the effect is dramatic: very high resonance can make the filter begin to self-oscillate, resulting in the filter generating a sine wave.
Envelopes and LFOs: movement over time
A static filter sounds lifeless. Modulation is what brings it to life.
Apple describes several ways to animate a filter, including envelope and LFO modulation, keyboard tracking and modulation-wheel control. An LFO, or low frequency oscillator, provides a waveform that modulates the signal.
- Amp envelope: shapes loudness through attack, decay, sustain and release.
- Filter envelope: opens or closes the cutoff over the life of a note.
- LFO: adds repeating motion such as wobble, vibrato or tremolo.
A short attack and quick decay on the filter envelope gives a plucky bass. A slow attack gives a pad that gradually brightens as it swells.
A practical starting patch
Try this to hear every stage working together.
- Select a sawtooth on the first oscillator and leave the filter fully open.
- Choose a low pass filter and slowly pull the cutoff down until the tone is warm.
- Add a little resonance and sweep the cutoff again.
- Send the filter envelope to the cutoff with a fast attack and short decay.
- Set the amp envelope for the sound you want: short release for plucks, long for pads.
Change one control at a time and listen. That habit teaches you more than any preset library.
When you have this workflow down, compare it with other approaches. Our overview of synthesis covers the wider field, and fm synthesis builds sound in a very different, additive-feeling way, without a filter-first mindset.
Common problems and how to fix them
Most weak patches come down to a handful of habits. Each has a quick remedy that stays within the oscillator, filter and envelope chain.
- The sound is thin: switch to a richer waveform such as a sawtooth, or add a second oscillator, so the filter has more harmonics to work with.
- The sound is harsh: lower the cutoff a little, or reduce the resonance, so the peak around the cutoff stops dominating.
- The sound is static: route an envelope or an LFO to the cutoff so the brightness changes while the note plays.
- Notes clip or click: check the amp envelope. A very abrupt attack or release can cause audible clicks, so soften them slightly.
Treat these as starting points rather than rules. Your ears and the context of the mix decide what works.
Why the filter is the heart of the sound
Two patches can use the same oscillator and still sound completely different. The difference is nearly always the filter and how it moves.
A fixed cutoff gives a consistent tone. A cutoff that opens and closes with each note gives the sound a sense of life and expression, which is why this one routing appears in so many presets.
It also explains why subtractive patches are so easy to adjust. Because everything flows in one direction, from source to filter to amplifier, you can change a single stage and hear exactly what it contributes. That makes the method a friendly place to learn before moving to more complex designs.
Frequently asked questions
Why is it called subtractive?
Show answer
Because the filter removes parts of a harmonically rich sound rather than adding components to build it.
Which waveform should I start with?
Show answer
A sawtooth is the usual choice, since it contains both even and odd harmonics at a relatively high amplitude, giving the filter plenty to shape.
What does resonance do?
Show answer
It emphasizes or suppresses signals around the cutoff frequency, changing the timbre of the sound.
Do I need a hardware synth?
Show answer
No. The same oscillator, filter and envelope layout appears in software instruments, so the concepts transfer directly.
