Subtractive synthesis filters harmonically rich oscillator output to sculpt timbre

Subtractive synthesis — the dominant East Coast approach — starts with a harmonically rich waveform (sawtooth, square) and removes (subtracts) unwanted frequency content via a filter. The signal chain is: VCO → VCF → VCA. The VCO provides raw harmonic material; the VCF shapes timbre by attenuating above the cutoff; the VCA shapes loudness over time via an envelope. This is called “subtractive” because you are removing harmonics rather than adding them (contrast with additive synthesis). The filter sweep is the defining expressive gesture: opening the filter brightens the sound; closing it darkens it. The 303, most Moog synths, and the majority of classic analog instruments use this architecture.

Examples

A sawtooth VCO → LPF VCF (cutoff swept by ADSR) → VCA (gated by same ADSR) produces the classic analog synth voice. The same patch with a square wave instead of sawtooth has a hollower, more woodwind-like tone because square waves lack even harmonics.

Assessment

Explain why starting with a sine wave in subtractive synthesis is usually limiting. Identify the three core modules in a standard subtractive voice and their order in the signal path.