Filters and Resonance

Cutoff sets brightness; resonance decides which band around the cutoff speaks first.

Related

TimbreMinimoogMoog modular synthesizerModern

The question

The same sawtooth sounds muffled with the cutoff low and harsh with it high; add resonance and one note steps forward. Why do these two controls move together?

How it works

A low-pass lets everything below the cutoff through and rolls off the rest at a fixed slope, often 12 or 24 dB per octave. The cutoff is no brick wall. Resonance creates a peak at the cutoff and lifts that band; a narrow, tall peak reads as a howl or whistle. High-pass, band-pass and notch move the passing region elsewhere. The filter also shifts phase, so stacked layers may lose alignment. At high cutoff and strong resonance a digital filter can self-oscillate.

Settings and what you hear

As the cutoff falls, sibilance and air go first, then midrange detail, until only lows remain. Moderate resonance gives a vocal edge; too much masks the fundamental. Envelope amount sets how much brighter the attack is, and key tracking opens the cutoff up high. A steep slope sweeps like a switch; a gentle one stays natural.

What to listen for

Play a sustained sawtooth and sweep the cutoff down. The level barely changes while the top disappears. Raise resonance and hear whether one note stands out or the low end turns nasal. Compare 12 dB and 24 dB; the first sweeps softly, the second cuts harder.

Common misconceptions

That cutoff is volume; that resonance means brighter; that a filter changes tone only, when slope and phase alter blend and timing.

Sources

• Gordon Reid, Sound On Sound Synth Secrets — filter and resonance behaviour checked, not quoted
• Udo Zölzer, DAFX — Digital Audio Effects, filter chapter checked, not quoted

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