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.
