short-description: Karplus-Strong sympathetic resonator for droning and plucked textures, with chord & tanpura tunings, arpeggiator, pitch tracking and web-configurable CV/pulse outputs.
draft: false
Name: Resonator
Language: C++ (Pico SDK + ComputerCard)
Creator: Johan Eklund
Version: 1.2.1
Status: Released
License: GPL-3.0
Editor: https://johaneklund.io/resonator
date-created: 2026-04-10
date-updated: 2026-08-18

tags:
  - effect
  - resonator
  - karplus-strong
  - drone
  - plucked

summary: |
  Four-string sympathetic resonator inspired by Rings/tanpura techniques.
  Feed audio to excite resonant strings, or trigger plucks with PulseIn1.
  X sets base pitch (or fine tune with CV1 connected), Y sets damping, Main sets wet/dry mix.
  PulseIn2 or short Z-down press advances chord mode; long Z-down hold resets progression defaults.

panel:
  inputs:
    - id: AudioIn1
      name: Excitation Input Left
      description: Mixed with AudioIn2 to excite resonator strings
    - id: AudioIn2
      name: Excitation Input Right
      description: Mixed with AudioIn1 to excite resonator strings
    - id: CVIn1
      name: Pitch CV
      description: 1V/oct pitch input; X knob becomes fine tune when connected
    - id: CVIn2
      name: Damping CV
      description: Modulates damping/decay with Y knob as base setting
    - id: PulseIn1
      name: Pluck Trigger
      description: Injects noise burst to excite all strings
    - id: PulseIn2
      name: Next Chord Trigger
      description: Advances to the next chord in progression
  outputs:
    - id: AudioOut1
      name: Resonator Output Mid
      description: Wet/dry mixed output using summed string image
    - id: AudioOut2
      name: Resonator Output Side
      description: Wet/dry mixed output using alternate stereo string image

controls:
  knobs:
    - when: { z: middle }
      main:
        name: Wet Dry Mix
        description: Blends direct excitation audio with resonator output
      x:
        name: Base Pitch
        description: Fundamental pitch (or fine tune with CV1 connected)
      y:
        name: Damping
        description: Higher values increase resonance length
    - when: { z: up }
      main:
        name: Wet Dry Mix
      x:
        name: Base Pitch
      y:
        name: Damping
    - when: { z: down, gesture: momentary }
      main:
        name: Next Chord
        description: Short press advances to next progression chord
    - when: { z: down, gesture: hold }
      main:
        name: Factory Reset Progression
        description: Hold about 3 seconds to restore all 18 default chord modes
    - when: { z: up, gesture: toggle }
      main:
        name: Tuning Mode
        description: Soloes first string for tuning/reference

  leds:
    - when: { z: any }
      display: list
      items:
        - id: LED0
          name: Progression Position Indicator A
          description: Encodes current progression slot with LED combination map
        - id: LED1
          name: Progression Position Indicator B
          description: Encodes current progression slot with LED combination map
        - id: LED2
          name: Progression Position Indicator C
          description: Encodes current progression slot with LED combination map
        - id: LED3
          name: Progression Position Indicator D
          description: Encodes current progression slot with LED combination map
        - id: LED4
          name: Progression Position Indicator E
          description: Encodes current progression slot with LED combination map
        - id: LED5
          name: Progression Position Indicator F
          description: Encodes current progression slot with LED combination map

host:
  usb:
    - name: Resonator Web Editor
      role: editor
      description: Browser editor for chord progressions and CV & pulse I/O