Pip Filter

ALM Busy Circuits 4HP
FILTER VCF VCA

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Compact 2-pole 12dB/oct lowpass filter with resonance, pingable trigger input, and built-in VCA normalled open. Self-oscillates with rough 1V/oct tracking from the second frequency input.

Patch Ideas · 5

★ Pinged percussion voice
Res just below self-osc · clock → Trig · Freq knob sets pitch · output is a decaying plucked tone with no audio input · attach envelope → VCA CV to add amplitude shaping
▸ Show diagram
Patch diagramPatch diagram with 4 modules and 3 connections. Modules: Pip Filter, Clock, Envelope, Output. Signals: 1 audio, 1 cv, 1 trigger.Pip FilterClockEnvelopeOutputRes: just below self-oscFreq: sets pitchTrigtrigVCAcvOutaudioOuttrigOutcvInaudio121. pings resonant peak2. amplitude shapeaudiocvtrigger
Rough sine VCO
Res fully CW → self-oscillates · Sequencer V/oct → Freq CV 2 · output is sine following pitch · use Freq CV 1 (attenuverter) for vibrato LFO
▸ Show diagram
Patch diagramPatch diagram with 4 modules and 3 connections. Modules: Pip Filter, Sequencer, LFO, VCA. Signals: 1 audio, 1 cv, 1 pitch.Pip FilterSequencerLFOVCARes: full CW (self-osc)-/+: ~2 o'clockFreq1v/oct-/+cvOutaudioV/oct1v/octOutcvInaudio11. attenuverted vibratoaudiocvpitch
★ Ducked filter sweep
Audio → In · envelope → VCA CV (ducks volume under filter sweep) · LFO → Freq CV 1 attenuverted for bipolar cutoff modulation · built-in VCA saves a dedicated VCA module
▸ Show diagram
Patch diagramPatch diagram with 5 modules and 4 connections. Modules: Pip Filter, VCO, LFO, Envelope, Output. Signals: 2 audio, 2 cv.Pip FilterVCOLFOEnvelopeOutputFreq: ~noonRes: moderate-/+: ~1 o'clockInaudio-/+cvVCAcvOutaudioOutaudioOutcvOutcvInaudio121. bipolar cutoff sweep2. amp shape in-moduleaudiocv
Self-patched resonance drone
Res full CW · slow LFO → Freq CV 1 attenuverted · no audio input · drifting sine drone at sub-audio to mid frequencies · excellent for ambient or modulating bass
▸ Show diagram
Patch diagramPatch diagram with 3 modules and 2 connections. Modules: Pip Filter, LFO, Mixer. Signals: 1 audio, 1 cv.Pip FilterLFOMixerRes: full CWFreq: low-mid range-/+: ~1 o'clock-/+cvOutaudioOutcvInaudio121. slow drift2. sine droneaudiocv
★ Pluck with pitched ping
Sequencer V/oct → Freq CV 2 · Res just below self-osc · trigger pattern → Trig · filter pings in tune with sequence · no VCO needed · acoustic-like plucked melody
▸ Show diagram
Patch diagramPatch diagram with 3 modules and 3 connections. Modules: Pip Filter, Sequencer, Reverb. Signals: 1 audio, 1 pitch, 1 trigger.Pip FilterSequencerReverbRes: just below self-oscFreq: tuned to A2Freq1v/octTrigtrigOutaudioV/oct1v/octGatetrigInaudio11. pitched plucksaudiopitchtrigger

Behaviors

Self-oscillation as sine source Res at full CW, no audio input

With resonance near maximum the filter oscillates into a sine wave even without audio input. Pitch follows the Freq knob plus both CV inputs. Freq CV 2 provides rough 1V/oct for a crude but usable sine VCO.

Ping mode trigger → Trig (with Res just below self-osc)

A trigger into Trig excites the resonant peak, producing a decaying plucked/sine-burst tone with no audio input needed. Resonance setting determines decay length — closer to self-osc = longer ring. Rising-edge detection prevents double pings from long gates.

Normalled-open VCA VCA input unpatched

The built-in VCA stays fully open when nothing is patched into its CV jack, so the module behaves as a plain filter by default. Patching a CV (envelope, LFO) adds amplitude control without requiring an external VCA.

Attenuverter offset via Freq CV 1 CV 1 patched · attenuverter active

The first frequency input has a built-in attenuverter, letting the same modulation source open or close the filter depending on knob position. Useful for inverting envelope polarity or scaling a bipolar LFO into a narrow sweep range.

Dual-input frequency summing both CV inputs patched

Freq knob, attenuverted CV 1, and raw CV 2 (1V/oct) all sum to set cutoff. Lets pitch tracking (CV 2) coexist with modulation (CV 1) without an external mixer — useful for a self-oscillating sine VCO that also accepts vibrato.

Controls

Freq CV 1 -/+ Attenuverter for the first frequency CV input. Scales CV positively or negatively around the manual Freq setting.
full CCW: invert · noon: zero · full CW: unity
global Freq Manual cutoff frequency. Summed with both CV inputs.
combined with CV 1 (attenuverted) and CV 2 (1V/oct)
global Res Manual resonance. Peaks signal just around the cutoff, reaches self-oscillation near full CW.
no CV input · self-osc approximately tracks V/oct from Freq CV 2

I/O

IN · 5

  • -/+ (Freq CV 1) 0-5V · attenuverted CV
    First frequency CV input with attenuverter. Summed with knob and second CV.
  • Freq (CV 2) 0-8V · rough 1V/oct CV
    Second frequency CV input. Wider range, roughly tracks 1V/oct when self-oscillating.
  • Trig rising-edge trigger · resonance must be just below self-osc to hear ping GATE
    Pings the filter to produce a plucked/percussive tone. Rising-edge only to prevent double pings from longer gates.
  • VCA 0-5V CV
    CV for the built-in VCA. Controls output level independently of cutoff.
    NORM → fully open (+5V equivalent) when unpatched
  • In audio AUDIO
    Audio input to the filter.

OUT · 1

  • Out audio AUDIO
    Audio output post filter and post VCA.