Bitwig OSC Translator & Chromatic Scale Transitions

Aspirtakis Agamemnon

Uncategorized

October 28, 2025

I built a Bitwig OSC Translator that listens to OSC messages from external controllers / sensors and turns them into Bitwig actions, device parameters, and musical note events. On top, it includes a Chromatic Scale Transition engine that morphs incoming notes between scales in real time — perfect for data-driven performance and generative sets.

What it does

  • OSC → Bitwig: Map any OSC path to Bitwig device parameters, clips, macros, transport, or note events.
  • Bi-directional (optional): Mirror selected Bitwig parameters back out as OSC for visual feedback.
  • Chromatic Scale Transitions: Constrain notes to a target scale, then morph to another scale (and octave) smoothly over time or on triggers.
  • Scene-aware: Each scene or track can have its own scale, octave, and transition rules.

System architecture

OSC Sources (sensors, apps) → Node.js Translator → WebSockets/OSC → Bitwig (Controller Script) → Instruments

  • Node.js Translator
    • Receives OSC (UDP/TCP)
    • Normalizes ranges (0–1, bipolar, dB, Hz)
    • Routing rules (per device/track)
    • Scale engine (quantize + morph)
  • Bitwig Controller Script
    • Exposes track/parameter endpoints
    • Triggers notes, macros, sends, clip actions
    • Optional return-channel for LEDs/meters

Mapping examples

OSC → Parameter

  • /city/noise → Track 1 Filter Cutoff (0–1 → 30 Hz–16 kHz)
  • /light/level → Master Reverb Send
  • /motion/speed → LFO Rate on Mod Device

OSC → Note

  • /grid/x = pitch seed, /grid/pressure = velocity
  • Quantize to D Phrygian for Track 2; when Scene changes, transition to E Harmonic Minor over 8 bars.

Chromatic Scale Transitions (how it “morphs” scales)

  1. Quantize: Incoming MIDI/derived pitch snaps to current scale (e.g., C Minor).
  2. Transition Curve: Over a defined period (beats/ms/bars) the scale set interpolates to a new one.
  3. Strategies (selectable per track):
    • Nearest-Note: always move to closest in the target scale.
    • Directional: push notes upward or downward during morph.
    • Weighted Chromatic: allow chromatic passing tones with decay.
  4. Octave Policy:
    • Fixed, Wrap, or Follow-Velocity (strong hits jump octave).
  5. Event Triggers:
    • Scene launch, clip end, OSC flag (/scale/next), or threshold (e.g., noise>0.7).

Typical performance setup

  • Track 1: Drums, OSC maps crowd density → groove amount, light → transient shaper.
  • Track 2: Polysynth, notes from sensor grid → quantize to A Dorian, scene change → C Lydian (4-bar morph).
  • Track 3: Bass, chromatic glide to E Phrygian on breakdown; octave follows motion intensity.

Routing & config (concise)

  • Ports: OSC in :9000, OSC out :9001.
  • Profiles: JSON files per project with:
    • sources: OSC paths, scaling, smoothing
    • routes: path → track.parameter or path → note
    • scales: per scene/track plus transition time, strategy, octave policy
  • Smoothing: Exponential or moving average to avoid zipper noise.
  • Safety: Range clamps, denormalization guard on very low levels.

Why Bitwig?

  • Modulators everywhere, per-note expressions, and a friendly Controller API make it ideal for data-driven performance and adaptive harmony.

Use cases

  • City Heart Modulation: Amsterdam sensor feeds reshape harmony globally.
  • Installations: Visitors’ movement alters both mix parameters and tonal center.
  • Live sets: One fader morphs an entire show from minor darkness to bright Lydian.
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