Liquid filter


Ripples delivers a classic, big-sounding analog four-pole filter in a small 8-HP package, continuing Mutable Instruments’ lineage of warm and tasty filters started by the Shruthi SMR4 mkII and 4-Pole Mission.

3 filter modes are available: 2-pole band-pass, 2-pole low-pass, and 4-pole low-pass.

Self-oscillation is available for all modes and produces a clean sine-wave on the LP4 output. Unlike many classic 4-pole designs, this filter does not suffer from “loudness drop” when resonance is increased. The resonance loudness compensation circuit brings a slight tone coloration reminiscent of the Roland SH/Jupiter filters, with a very round and “liquid” resonance.

The 4-pole low-pass output is additionally sent to a VCA. This makes Ripples a good “final stage” module for an inexpensive/space-constrained subtractive synthesis synth voice



  • Signal in
  • Frequency CV 1 (1V/Oct)
  • Resonance CV. Self oscillation starts at 4V. Control voltages above 5V are non-linearly compressed, for fine control of resonance overdrive
  • Frequency CV 2 (with bipolar attenuator, from -1V/Oct to 1V/Oct)
  • VCA level. Control voltages above 5V are non-linearly compressed.


  • Cutoff frequency, 18Hz to 18kHz
  • Resonance (self oscillation at 80%)
  • Attenuverter on Frequency CV


  • 2-pole BP
  • 2-pole LP
  • 4-pole LP
  • 4-pole LP attenuated by VCA

Technical characteristics

  • Fully analog, based on SSM2164 low noise/distortion quad VCA chip, and LM13700 OTA for that extra bit of non-linearity.
  • Frequency CV inputs impedance: 100k.
  • Audio input impedance: 75k.
  • Resonance and VCA CV input impedance: 30k.
  • Open-source hardware.
  • 8-HP.
  • Current consumption: +12V: 35mA ; -12V: 35mA.