Bach-AI: Soprano and Bass Chorale Generator

A generative AI project that composes two-part harmony in the style of J.S. Bach. Given a soprano melody, the system learns to generate a counterpoint bass line using LSTM neural networks trained on the JSB Chorales corpus.

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📁 Project Structure

File	Description
train.py	Trains an LSTM model on soprano-only melodies
generate.py	Generates soprano-only output from chorale_lstm.pt
train_bass.py	Trains a bass model conditioned on existing soprano lines
generate_bass.py	Generates a bass line given a soprano sequence and trained bass_lstm.pt
train_joint_bass_and_soprano.py	Trains a joint model that learns soprano + bass interaction in interleaved form
generate_joint_bass_and_soprano.py	Generates both soprano and bass lines using the joint model joint_lstm.pt
bach_dataset.py	Loads JSB chorale data and processes them into token sequences
model.py	Contains the PyTorch ChoraleLSTM class definition

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🧪 Setup

This project uses uv for dependency management:

uv venv && source .venv/bin/activate
uv pip install -r uv.lock

To install dependencies manually:

uv pip install torch music21

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🚦 Training

Soprano-only:

python train.py

Saves model to chorale_lstm.pt

Bass conditioned on soprano:

python train_bass.py

Saves model to bass_lstm.pt

Joint Soprano + Bass modeling:

python train_joint_bass_and_soprano.py

Saves model to joint_lstm.pt

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🎼 Generation

Generate Soprano Only:

python generate.py

Creates output/generated.mid and generated.xml

Generate Bass from Soprano:

python generate_bass.py

Loads chorale_lstm_with_keys.pt and bass_lstm.pt, creates output/soprano_bass.mid

Generate Joint Soprano + Bass:

python generate_joint_bass_and_soprano.py

Parses generated.xml, completes with bass, saves to output/joint_generated.mid/xml

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🎧 Examples

Inside examples/ you'll find chronological generations:

File	Description
generated.xml/mid	Soprano-only melody
soprano_bass_old.mid/xml → _old_1 → _old_4	Early attempts at melody-conditioned bass generation
joint_generated.xml/mid	✅ Best result to date — generated using the interleaved Soprano + Bass joint model

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📚 Dependencies

• PyTorch
• music21
• uv (package manager)

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🚀 TODO

• Add Alto and Tenor for full SATB
• Visualization (piano roll / staff preview)
• Longer-form chorale generation
• Music-theory-aware loss constraints

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🧠 Credits

Built by Timothy Williams using open-source data from music21.

Inspired by J.S. Bach's chorale harmonizations.

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