Mutable Instruments Ripples Liquid Filter

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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.


Ripples demos



Ripples overview from Equinoxoz music solutions on Vimeo.



  • 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.

Ripples user manual


Mutable Instruments’ Ripples is a voltage-controlled filter. It provides 3 output modes: 2-pole band-pass, 2-pole low-pass and 4-pole low-pass. The filtering is achieved by a high-quality quad VCA. An OTA in the filter feedback path brings the resonance under voltage control, and also serves as a soft-limiter to ensure a clean self oscillation. Finally, a VCA allows the level of the 4-pole low-pass output to be modulated by a CV. This makes Ripples a good “final stage” module for a subtractive synthesis patch.

The tonal character of the filter is inspired by japanese classics from the 80s.

Download the quick start guide.


Mutable Instruments’ Ripples is designed for Eurorack synthesizer systems and occupies 8 HP of space. It requires a +/- 12V power supply, consuming 35mA from each supply rail. The red stripe of the ribbon cable must be oriented on the same side as the “Red stripe” marking on the printed circuit board.


A: Resonance level. Self-oscillation occurs at about 80% of the course of this potentiometer.

BCutoff frequency.

C: Frequency modulation attenuverter. Adjusts the amount and polarity of frequency modulation from the FM input.

Inputs and outputs

RES: Resonance control voltage, added to the value set by the RES knob. A control voltage of +4V starts bringing the filter to self-oscillation. Control voltages above +5V are compressed and only bring a moderate increase of the loudness of the self-oscillation tone.

FREQ: 1 V/Oct cutoff frequency control. This input is very helpful for getting the filter frequency to track the keyboard note. Notice that when resonance is set to its maximum value, with no input signal, Ripples behaves like a sine wave oscillator. The LP2 and BP2 outputs produce a slightly distorted sine-wave. The LP4 output produces a clean output.

FM: Cutoff frequency CV. This signal is attenuated and polarized by the corresponding knob.

IN: Signal input. This input is DC-coupled. However, the internal connection between the VCF output and the VCA stage is AC-coupled.

GAIN: VCA control voltage. This voltage controls the level of the signal produced at the LP4>VCA output. 0V silences the signal; 5V applies a unitary gain. Values above +5V are progressively compressed.

BP2: 2-pole band-pass output.

LP2: 2-pole low-pass output.

LP4: 4-pole low-pass output.

LP4>VCA: 4-pole low-pass output sent into a VCA.

Calibration procedure

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