Subtractive Synthesis

Start with a harmonically rich waveform and carve the tone with a filter and envelope.

Related

TimbreEqualizerMinimoogModern

The question

Why does the same oscillator become a brass section in one patch and a harmonica in another? Subtractive synthesis starts with a harmonically rich wave and removes what the ear does not need.

How it works

A sawtooth contains every integer harmonic, a square the odd ones, and both are brighter than a sine. A filter follows the oscillator; a low-pass rolls off everything above the cutoff. Resonance at the cutoff makes one band speak first. An envelope moves the cutoff over time, so the attack can be brighter than the sustain. A second envelope shapes level, and together they decide what instrument the ear hears.

Settings and what you hear

Cutoff sets brightness, resonance sets emphasis around the cutoff, and envelope amount sets how much brighter the attack is. A low cutoff sounds muffled; raising it reveals midrange and an edgy top. Too much resonance masks the fundamental and can whistle. Key tracking opens the cutoff in the high register so the top notes do not go dull.

What to listen for

Play a saw chord and sweep the low-pass down. Notice the level hardly drops while the top disappears. Compare a slow attack with a fast one; the first reads as a pad, the second as a pluck. On bass, hear whether resonance makes a note jump out.

Common misconceptions

That subtractive synthesis only imitates old analogue synths; that resonance is a brightness control; that a filter changes only tone, when it also shifts level and phase.

Sources

• Gordon Reid, Sound On Sound Synth Secrets — subtractive synthesis principles checked, not quoted
• Udo Zölzer, DAFX — Digital Audio Effects, filters and oscillators chapter — background checked, not quoted

Used for fact-checking only; all prose is original.