The principle
You start from a waveform rich in harmonics and remove with a filter what you do not need. It is the method of classic analog synths (Minimoog, Jupiter-8, Prophet-5) and of most virtual synths.
Signal path
- Oscillators: sawtooth (all harmonics, bright), square and pulse (odd harmonics, hollow; the pulse width changes the timbre), triangle, sine. Often two or three slightly detuned oscillators (±5–15 cents) for thickness.
- Mixer and noise: white for breaths and attacks, pink for textures.
- Filter: low-pass 12 dB/oct (soft) or 24 dB/oct (classic, more decisive); Cutoff (cutoff frequency) and Resonance (emphasis around the cutoff). Key tracking makes the filter open on high notes.
- Amplifier with envelope.
- Modulations: envelopes and LFOs on pitch, filter, volume, pulse width.
Basic recipes
- Bass: saw + square sub an octave below, LP 24 dB with cutoff 300–800 Hz, filter envelope with short decay for a “spoken” attack.
- Pad: two detuned saws, slow attack, half-closed filter, chorus.
- Brass: saw, filter envelope with a 50–100 ms attack that opens the sound like a wind instrument.
- Lead: saw or square, glide 30–80 ms, vibrato with an LFO at 5–6 Hz fading in with a delay.
Link with theory
Filters work on harmonics: with the cutoff at 1 kHz a C2 (65 Hz) keeps about the first 15 harmonics, a C5 (523 Hz) only the first: this is why key tracking is needed.
Real-world example
The riff of “Jump” by Van Halen (1984) is played on an Oberheim OB-Xa: filtered, detuned sawtooth waves, a subtractive brass sound that became iconic. In funk, Bernie Worrell's Minimoog bass in “Flash Light” by Parliament (1977) is another classic.