thonk-double-bubble

Thonk Synth Double Bubble

Dual multi-mode filter

16 HP Eurorack module

Double Bubble is a 16HP dual analog multimode Eurorack filter. Each channel offers low-pass, high-pass, band-pass, and notch responses, with independent, linked-stereo, parallel, and serial operation plus spacing, cross-modulation, and feedback.

Features

  • Two independently configurable filter channels can operate separately, linked for stereo control, in parallel, or in series.
  • Spacing moves the two cutoff frequencies in opposite directions from their current settings.
  • Bidirectional cross-modulation uses each filter output to modulate the other filter's cutoff.
  • A voltage-controlled, bipolar feedback path mixes Output B back into Input A for tonal shaping, distortion, and self-oscillation.
  • Each input-level stage can drive its analog filter core into asymmetrical soft clipping.
  • Frequency CV A and V/Oct A are normalled to their Channel B counterparts, while the channel controls remain independent.
  • Either filter can self-oscillate and operate as a voltage-controlled tone source.
  • Optional per-channel low-pass resonance compensation preserves bass and perceived level as resonance increases.
  • Per-channel movement LEDs show cutoff direction and speed, including audio-rate modulation.
  • Remember: switch off the case power before installation and align the cable's red line with the red rear-panel text; the module includes reverse-polarity protection.

Controls & Jacks (41)

  • Frequency CV Attenuverter B— Scales and inverts the signal at Frequency CV B or its normalized feed from Frequency CV A; fully clockwise provides approximately 1 V/octav
  • Input Level A— Controls Channel A's input level and can drive the analog filter core into asymmetrical soft clipping.
  • Input Level B— Controls Channel B's input level and can drive the analog filter core into asymmetrical soft clipping.
  • Frequency CV Attenuverter A— Scales and inverts the signal at Frequency CV A; fully clockwise provides approximately 1 V/octave response.
  • Frequency B— Sets Channel B's base cutoff frequency from approximately 20 Hz to 20 kHz; it is ignored while Link is enabled.
  • Spacing— Offsets the two cutoff frequencies in opposite directions; clockwise raises Channel B and lowers Channel A, while counterclockwise does the
  • Frequency A— Sets Channel A's base cutoff frequency from approximately 20 Hz to 20 kHz; when Link is enabled it also sets Channel B's base cutoff.
  • Feedback— Controls the level and polarity of Output B fed back into Input A; clockwise gives non-inverted feedback, counterclockwise gives inverted fe
  • Feedback CV— Control input for feedback amount and polarity; when patched, the Feedback knob attenuates and inverts the incoming modulation.
  • Mode A BP Indicator— Lights when Channel A is in two-pole band-pass mode with 12 dB/octave slopes on each side.
  • Serial Mode— Selects Channel B's normalized source: enabled routes Output A into Input B for serial filtering, while disabled routes a copy of Input A in
  • Input A— Audio input for Channel A; its signal is also normalled to Channel B when Input B is unpatched and Serial Mode is disabled.
  • Resonance B— Controls Channel B resonance; settings above roughly three o'clock can make the filter self-oscillate.
  • Spacing CV— Bipolar -10 V to +10 V modulation input for moving the two channel cutoff frequencies in opposite directions; the Spacing knob becomes its a
  • Frequency CV B— Bipolar cutoff-frequency modulation input for Channel B, accepting approximately -10 V to +10 V; when unpatched it receives the signal from
  • V/Oct B— Unattenuated precision 1 V/octave cutoff-frequency input for Channel B; patching it overrides the normalization from V/Oct A.
  • Frequency CV A— Bipolar cutoff-frequency modulation input for Channel A, accepting approximately -10 V to +10 V and controlled by Frequency CV Attenuverter
  • V/Oct A— Unattenuated precision 1 V/octave cutoff-frequency input for Channel A, also normalled to Channel B when V/Oct B is unpatched.
  • Output B— Channel B filter audio output, also used internally as the source of the feedback path to Channel A.
  • Input B— Audio input for Channel B; patching it overrides the internal routing selected by Serial Mode.
  • XMOD CV— Shared 0 V to +5 V control input for the overall cross-modulation amount; XMOD A and XMOD B independently attenuate it.
  • Output A— Channel A filter audio output.
  • Mode B— Press to advance Channel B through low-pass, high-pass, band-pass, and notch modes.
  • XMOD B— Sets how much of Output A modulates Channel B's cutoff frequency.
  • XMOD A— Sets how much of Output B modulates Channel A's cutoff frequency.
  • Mode A Notch Indicator— Lights when Channel A is in notch mode.
  • Link— Links the large frequency controls so Frequency A sets the base cutoff of both channels and Frequency B is ignored; other modulation control
  • Resonance A— Controls Channel A resonance; settings above roughly three o'clock can make the filter self-oscillate.
  • Mode B Notch Indicator— Lights when Channel B is in notch mode.
  • Mode A HP Indicator— Lights when Channel A is in two-pole, 12 dB/octave high-pass mode.
  • Mode A— Press to advance Channel A through low-pass, high-pass, band-pass, and notch modes.
  • Frequency Movement A— Shows Channel A cutoff movement: pink for positive movement, green for negative movement, greater brightness for faster changes, and an appa
  • Frequency Movement B— Shows Channel B cutoff movement: pink for positive movement, green for negative movement, greater brightness for faster changes, and an appa
  • Input Clip A— Lights dimly with Channel A input audio and becomes brighter as the filter core approaches or enters clipping.
  • Input Clip B— Lights dimly with Channel B input audio and becomes brighter as the filter core approaches or enters clipping.
  • Link Indicator— Lights while Link is enabled.
  • Mode A LP Indicator— Lights when Channel A is in four-pole, 24 dB/octave low-pass mode.
  • Mode B HP Indicator— Lights when Channel B is in two-pole, 12 dB/octave high-pass mode.
  • Mode B LP Indicator— Lights when Channel B is in four-pole, 24 dB/octave low-pass mode.
  • Serial Mode Indicator— Lights when Serial Mode is enabled; this selects the Output A to Input B normalization, which is overridden when a cable is patched into Inp
  • Mode B BP Indicator— Lights when Channel B is in two-pole band-pass mode with 12 dB/octave slopes on each side.

How-To Guides

  • Dual Mono Filters
  • Mono In, Stereo Out Filter
  • Stereo In, Stereo Out Filter
  • Variable Width Band Pass
  • Double Notch Phaser
  • Formant Filtering
  • FM Oscillator

Explore the interactive Double Bubble panel on BleepDex — tap any control to learn what it does.

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