Voltage-Controlled Filter (VCF)

A clean, resonant state-variable filter that gives you low-pass, band-pass, and high-pass outputs at once from a single input. With its built-in drive stage it covers everything from gentle tone-shaping to screaming, self-resonant acid lines.

How it works

The filter runs a Cytomic state-variable design, so all three responses are computed simultaneously and stay perfectly in tune with each other. The large response display isn't just a readout — it's the main control: drag across it to sweep, with horizontal motion setting cutoff and vertical motion setting resonance, so diagonal drags carve a full sweep in one gesture. The amber, teal, and slate curves show the LP, BP, and HP outputs in real time, and a double-click resets both.

Controls

  • Response display — drag to set cutoff (←→) and resonance (↑↓) at once; the live curves show exactly what each output is doing.
  • Cutoff — dials the corner frequency for precise tuning; tracks 1V/oct so it can be played like a pitch.
  • Res — emphasis at the cutoff frequency; turn it up for a vocal peak, all the way for self-oscillation.
  • Drive — overdrives the signal into the filter with soft saturation; clean at zero, thick and harmonically rich as you push it.
  • FM / Res attenuverters — scale and invert the fm and res CV inputs; centred is off.

Inputs & outputs

  • In — the audio (or CV) signal to filter.
  • V/Oct — 1V/oct pitch control of the cutoff, for keyboard- or sequencer-tracked filtering.
  • FM — cutoff modulation; depth and polarity set by the FM attenuverter.
  • Res — resonance modulation; depth and polarity set by the Res attenuverter.
  • LP / BP / HP — low-pass, band-pass, and high-pass versions of the input, all available at the same time.

Tips

  • Patch an envelope to FM for classic plucky filter sweeps; flip the attenuverter negative for inverted, duck-style motion.
  • Crank Res toward the top with nothing patched to In and the filter sings — play it via V/Oct as a sine-ish oscillator.
  • Mix the LP and HP outputs together for a notch, or take BP alone for tight, telephone-style bands.