Simple Bach Chorale Corpus Pipeline

This project now uses one simple data source only: the built-in Bach chorale corpus in music21.

Installation

python -m venv .venv
.\.venv\Scripts\Activate.ps1
pip install -r requirements.txt

Run The Pipeline

python scripts/build_chorale_instances.py --start 1 --end 26 --numbering riemenschneider --target-voices 4 --include-roman --output-dir data/chorales_easy

What This Produces

• data/chorales_easy/instances/*.json (one file per chorale)
• data/chorales_easy/chorale_instances.jsonl (all instances in one file)
• data/chorales_easy/summary.json (run summary)

What Is Inside Each Instance

• Chord roots and chord durations from chordify()
• Starting pitches (voice-ordered)
• Constraints (max_melodic_step, forbidden_parallels, max_k, max_k1, max_k2, max_k3)
• Metadata with:
  • observed tangling (k, k1, k2, k3)
  • voice-leading interval stats
  • counterpoint checks (forbidden parallels and bass contrary motion)
  • Roman numerals when available (for early chorales)

Optional: Strict Filtering

If you only want chorales that satisfy no forbidden parallels and enough contrary bass motion:

python scripts/build_chorale_instances.py --start 1 --end 26 --numbering riemenschneider --target-voices 4 --include-roman --output-dir data/chorales_easy --require-no-forbidden-parallels --require-bass-contrary --bass-contrary-threshold 0.5

Data Contract

Schema file:

• schemas/problem_instance.schema.json