docs/step-1-demucs-setup.md

Step 1 — Demucs Setup

Status: DONE

What we did

Installed Demucs and ran it on a local audio file to confirm the model works before building anything around it.

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What was installed

# CPU-only PyTorch (saves ~2GB vs CUDA build — no GPU on this machine)
pip install torch torchaudio --index-url https://download.pytorch.org/whl/cpu

# Demucs model
pip install demucs

# Required for saving output audio files
pip install torchcodec

How to run it manually

source venv/bin/activate
demucs --two-stems=vocals -n mdx_extra "path/to/audio.mp3"

• -n mdx_extra — lighter model, faster on CPU
• --two-stems=vocals — splits into two files: voice and background

Output

Results land in:

separated/mdx_extra/<track-name>/
├── vocals.wav       # isolated voice
└── no_vocals.wav    # background / everything else

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Notes

• Processing time: ~40 seconds for a 33-second clip on ThinkPad X270
• Fan noise mixed into voice is not fully removed — Demucs is a music separator, not a speech denoiser
• Future fix: swap Demucs for DeepFilterNet (better for speech + background noise)
• Model weights cached at ~/.cache/torch/hub/checkpoints/ — no re-download on next run