entropic-loop-grackle

Entropic Loop Grackle

Three-operator phase-modulation voice with just-intonation ratios

20 HP Eurorack module

Grackle is a digital three-operator phase modulation (FM) synthesis voice from debut brand Entropic Loop, named to Perfect Circuit's Best of 2025. Two modulator operators feed one carrier through three switchable algorithms — Add, Multiply (with built-in 7-stage triangle wavefolder), or Cascade — and modulator pitches are set as just-intonation ratios using slider numerators (1-32) against a switchable denominator (3, 5, or 8). A built-in VCA envelope with logarithmic rise and exponential decay ships in three modes (Triggered one-shot, Asymmetric Slew, Cycling) and is normalled to the Mod 1 and Mod 2 Depth CV inputs for instant percussive movement. Audio-rate CV is accepted on every parameter, including the algorithm and interval denominator switches, and a Shift button unlocks fine-tuning, internal oscillator feedback, hard-sync, and a hidden chaotic Thomas attractor modulation source.

Features

  • Three-operator phase modulation: two modulators (Mod 1, Mod 2) and one carrier
  • Three switchable algorithms: Add, Multiply (with 7-stage triangle wavefolder), and Cascade
  • Just-intonation interval system: numerator 1-32 / denominator 3, 5, or 8
  • Built-in VCA envelope: logarithmic rise, exponential decay
  • Three envelope modes: Triggered (one-shot), Asymmetric Slew (gate-tracking), Cycling (free-run/LFO)
  • Internal envelope normalled to both Mod 1 and Mod 2 Depth CV inputs for instant percussive movement
  • Audio-rate CV control over every parameter, including algorithm and interval denominator switches
  • AC-coupled ActualFM input for linear FM from an external oscillator
  • Buffered Envelope Out as a standalone CV utility
  • Mod Out: pre-carrier modulator audio for filtering, feedback patches, or as standalone source
  • Shift button unlocks fine-tuning, internal feedback, hard sync, and a chaotic Thomas attractor mode
  • Hard sync via Shift + Decay slider top: phase resets on rising gate edges

Controls & Jacks (31)

  • Mod 1 Interval
  • Mod 1 Depth
  • Mod 2 Interval
  • Mod 2 Depth
  • Frequency
  • Growth
  • Decay
  • Frequency CV Attenuator
  • Growth CV Attenuator
  • Mod 1 Interval CV Attenuator
  • Mod 2 Interval CV Attenuator
  • Interval
  • Mod 1 Depth CV Attenuator
  • Mod 2 Depth CV Attenuator
  • Algorithm
  • Decay CV Attenuator
  • Envelope Mode
  • Interval 1 CV In
  • Interval 2 CV In
  • ActualFM In
  • Interval CV In
  • Gate In
  • Growth CV In
  • Carrier Out
  • Mod 1 Depth CV In
  • Mod 2 Depth CV In
  • 1V/Oct In
  • Algorithm CV In
  • Envelope Out
  • Decay CV In
  • Mod Out

How-To Guides

  • Classic Two-Operator Bell
  • Cascade Evolving Pad
  • Cycling Envelope as Audio-Rate Modulator
  • Multiply Wavefolder Lead
  • Thru-Zero FM Glissando
  • ActualFM External Voice

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

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