Multimode Filter

Parameters

Cutoff — Filter cutoff frequency in Hz, 20–20000. The frequency where the filter starts attenuating (lowpass), starts passing (highpass), or centers (bandpass / notch / peaking / shelves). For lowpass, content above cutoff is reduced; for highpass, content below. The filter response widget shows the current curve in real-time.

Resonance — Filter resonance, 0–1. Boosts a peak around cutoff, exaggerating the filter character. Low resonance (0–0.3) is gentle and transparent. Mid resonance (0.4–0.7) gives the classic “filter sweep” character. High resonance (0.8–1) approaches self-oscillation — the filter starts ringing on its own pitch, useful for sci-fi sweeps and drone effects. Each algorithm responds to resonance differently — Moog has a smooth musical resonance, 303 has the sharp acid-sweep character, ZDF stays clean even at high settings.

Drive — Pre-filter drive amount, 0–1 (visible only in 303 and Diode modes). Adds nonlinear saturation inside the filter feedback path — gives you the dirty, growling character of a pushed analog filter. 0 is clean; higher values progressively saturate. Essential for the 303 acid sound; useful in Diode for vintage character.

Dry/Wet — Equal-power blend between dry (0) and the filtered signal (1). At 1 you hear the pure filtered output; lower values blend the unfiltered signal back in.

Additional controls

Algorithm — Filter circuit model. Clean — neutral digital filter (Butterworth-style); transparent, surgical, full set of filter types. Moog — emulates the iconic Moog ladder filter; warm, musical resonance; lowpass / highpass / bandpass / band-reject only. 303 — emulates the Roland TB-303 filter; sharp, squelchy resonance, acid character. Diode — emulates the EMS / TB-303 diode-ladder topology; gritty character with strong drive interaction. ZDF — zero-delay-feedback topology; mathematically modern, very clean and stable across all settings. Default Clean for transparent EQ-style filtering; Moog/303/Diode for character and synth-style sweeps; ZDF for surgical work that still needs analog flavor.

Mode — Filter type. In Clean: LP (lowpass), HP (highpass), BP (bandpass), BPk (bandpass-peak), Ntch (notch), Peak (peaking EQ), LSh (low shelf), HSh (high shelf). In Moog/303/Diode/ZDF (which model resonant ladder filters): LP, HP, BP, BR (band-reject) only — the analog topologies don’t natively produce shelving curves.

Slope — Filter slope steepness, 12 dB/octave or 24 dB/octave. 12 dB is the gentler classic single-pole-pair slope (one round of filtering). 24 dB is steeper — twice the slope, sharper cutoff, more dramatic filtering effect. 24 dB is more “in your face” for sweeps; 12 dB is smoother for general tone shaping.

Gain — Boost / cut in dB for shelving and peaking modes only, −24 to +24 (visible only in Peaking, Low Shelf, High Shelf modes). Sets how much the band is boosted or cut. Hidden when filter mode doesn’t use it.

About Multimode Filter

Most modern multimode filters offer a choice of “circuit” — different ways to arrange the same basic filter math, each with subtly (or dramatically) different sonic character. K2K’s Multimode Filter gives you five: Clean for surgical work, Moog/303/Diode for analog character, and ZDF for clean modern stability. The math is genuinely different — they don’t sound the same and they don’t react to resonance or drive the same way. Try the same cutoff sweep through all five to hear the differences. For most tasks, Clean is the right starting point; switch to a vintage model when you specifically want its character.

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