draft: false
Name: Two Tracks
short-description: "Two Tracks — Dual-read-head phase looper. Record a mono loop to flash (IMA-ADPCM) and play it through two independent heads with separately controllable positions and loop lengths for evolving phase patterns and interference textures."
Language: C++ (Pico SDK + ComputerCard)
Creator: Joep Vermaat
contact:
  email: joep@joep-i.nl
  website: https://codeberg.org/johantv/
Version: 1.2
Status: Released
License: MIT
date-created: 2026-07-11
date-updated: 2026-07-27
Repository: https://codeberg.org/johantv/two-tracks

tags:
  - looper
  - phase
  - delay
  - dual-head

summary: |
  A dual-read-head audio looper inspired by Steve Reich's phase music.
  Record a loop and play it through two independent outputs with separately
  controllable read positions and loop lengths, creating evolving phase
  patterns and interference effects.

  Recording uses a hands-free three-state machine: PLAY -> ARMED -> RECORD -> PLAY.
  Z Down arms recording; a 3-second countdown with audible ticks begins; recording
  starts automatically when the countdown expires; Z Down again stops recording.

  Two play modes (Z switch selects after recording):
    Offset mode (Z Middle): each knob sets position offset within the loop.
    Phasing mode (Z Up): right loop is shorter than left, creating natural periodic
    phasing. Knob Y adds a speed offset on the right head.

  Audio is stored in flash as IMA-ADPCM (4 bits per sample). Capacity depends on
  the card: about 70 seconds on a 2 MB card, 11 minutes on a 16 MB card.

panel:
  inputs:
    - id: AudioIn1
      name: Audio In
      description: Mono audio input — recorded to the flash loop. Both read heads play back this single loop.
    - id: AudioIn2
      name: Audio In 2
      description: Unused (recording is mono).
    - id: CVIn1
      name: CV 1
      description: In Offset mode modulates left offset; in Phasing mode modulates right loop length.
    - id: CVIn2
      name: CV 2
      description: In Offset mode modulates right offset; in Phasing mode modulates right speed.
    - id: PulseIn1
      name: Pulse 1
      description: Resets the left read head to the loop start.
    - id: PulseIn2
      name: Pulse 2
      description: Resets the right read head to the loop start.
  outputs:
    - id: AudioOut1
      name: Left Out
      description: Left read head output.
    - id: AudioOut2
      name: Right Out
      description: Right read head output.
    - id: CVOut1
      name: CV 1
      description: Left head phase position (play), buffer fill (record), 0 (armed).
    - id: CVOut2
      name: CV 2
      description: Right head phase position (play), loop length (record), 0 (armed).
    - id: PulseOut1
      name: Pulse 1
      description: Unused.
    - id: PulseOut2
      name: Pulse 2
      description: Unused.

controls:
  switch:
    up:
      name: Phasing mode
      description: Right loop shorter than left, creating natural phasing. Y knob adds speed offset.
    middle:
      name: Offset mode
      description: Each knob sets position offset within the loop.
    down:
      name: Record arm / stop
      description: In PLAY arms recording (3s countdown); in RECORD stops and returns to PLAY.
  knobs:
    - main:
        name: Loop window / Right loop length
        description: In Offset mode controls the loop window length (tiny fragment -> full loop). In Phasing mode controls how much shorter the right loop is (short -> full).
      x:
        name: Left position offset / Right window start
        description: In Offset mode sets left head position offset. In Phasing mode sets where the shortened right window starts within the loop.
      y:
        name: Right position offset / Right speed
        description: In Offset mode sets right head position offset. In Phasing mode sets right playback speed (0.9x - 1.1x, centre = 1.0x).