Most synths you'll ever touch — hardware or software, vintage or modern — are built around the same three-stage idea called subtractive synthesis: generate a harmonically rich sound, then carve away the parts you don't want, then shape how it starts and stops over time. Learn this signal path once and nearly every synth's front panel stops looking like a wall of unlabeled knobs and starts looking like a familiar layout with different-shaped knobs.
Stage 1: The oscillator (generate)
The oscillator is the sound source — it generates a raw waveform at a given pitch. The waveform's shape determines its harmonic content, which is why different wave shapes have such different characters before any shaping happens:
- Sine — a pure tone, no additional harmonics, sounds smooth and hollow
- Sawtooth — bright and buzzy, rich in harmonics, a common starting point for leads and basses
- Square / pulse — hollow and reedy, strong odd harmonics, classic "video game" or woodwind-adjacent character
- Triangle — softer than a square wave, fewer harmonics, closer to a sine but with more presence
Most patches start by picking a waveform (or blending a few) because that choice sets the raw material everything downstream will work with.
Stage 2: The filter (subtract)
This is the "subtractive" part the whole technique is named for. A filter removes frequencies from the oscillator's raw signal. The most common type, a low-pass filter, lets low frequencies through and cuts high ones — turning a bright sawtooth into something duller and warmer as the filter closes. Two controls matter most:
- Cutoff frequency — where the filter starts removing content; lower cutoff means a darker sound
- Resonance — emphasizes frequencies right at the cutoff point, adding a whistly or squelchy edge as it increases
Sweeping the cutoff while a note plays is one of the most recognizable moves in electronic music — that classic "opening up" sound.
Stage 3: The envelope (shape over time)
The envelope controls how a parameter — usually volume — changes over the life of a note, using four stages, commonly abbreviated ADSR:
- Attack — how quickly the sound reaches full volume after a key is pressed
- Decay — how quickly it falls from that peak to the sustain level
- Sustain — the level it holds at while the key is held down (this one's a level, not a time)
- Release — how quickly it fades to silence after the key is released
Why this order matters
Oscillator, then filter, then envelope isn't arbitrary — it's the literal order the signal travels through on most synths, hardware or software. Once this three-stage path is second nature, a drum machine's individual voice controls, a software synth's plugin interface, and a vintage analog synth's patch bay all start reading as variations on the same idea, not three unrelated instruments to learn from scratch.