Filter Resonance

Resonance (also called Q or emphasis) feeds the filter's output back into its input, amplifying frequencies right at the cutoff point. Low resonance produces a gentle roll-off. Medium resonance adds a nasal, focused quality. High resonance creates a sharp, whistling peak that can dominate the sound. At maximum resonance, many filter designs self-oscillate — producing a pure sine tone at the cutoff frequency without any input signal. This self-oscillation can be used as a sound source itself. Resonance is crucial for acid bass lines, vocal-like formant sounds, and aggressive lead tones.