extract-vocals

Extract Vocals (demucs 2-stem)

Isolate vocals from a mixed audio file using demucs in 2-stem mode. Fast and focused — produces vocals.wav and accompaniment.wav. Optionally drop the accompaniment if the user only wants the vocal stem.

When to use

• The user wants vocals isolated from a song (e.g., for editing, re-recording, or remastering).
• Preparing a karaoke track — extract the accompaniment, discard vocals.
• Extracting a vocal guide from a podcast with music bed.
• Quick turnaround on a single stem (faster than 4-stem separate-stems).

Do not use this skill for:

• Full stem separation (drums, bass, other) → use separate-stems.
• Batch processing many files → use separate-stems with GPU for throughput.

Inputs

1. Input file — required. MP3, WAV, FLAC, M4A supported.
2. Output directory — defaults to vocals_<date>/ next to the input.
3. Keep accompaniment — boolean flag. Default: keep both stems. If false, delete the accompaniment stem and keep only vocals.wav.
4. GPU flag — optional. Pass --gpu to use CUDA; default is CPU.

Procedure

1. Check if demucs is on PATH (which demucs). If missing, point the user at install-deps and note the ~2 GB download on first run.

2. Build the command:

   demucs \
     --two-stems vocals \
     -d <device> \
     -o "<output-dir>" \
     "<input-file>"
   

   Set -d cuda for GPU, -d cpu for CPU. Default is CPU.

3. Monitor progress and capture stderr.

4. After processing:

   • If keep_accompaniment is false, delete the accompaniment stem: rm "<output-dir>/accompaniment.wav".
   • Else, leave both stems in place.

5. Verify output: confirm vocals.wav is present and non-zero size. If accompaniment was kept, confirm that too.

Output

• Two WAV files (or one if accompaniment was dropped):
  • vocals.wav — isolated vocal track.
  • accompaniment.wav — (optional) instrumental/music bed, kept only if requested.
• Summary: <input> → <output-dir> (vocals + accompaniment, 2-stem mode) or (vocals only) if accompaniment was dropped.

Notes

• 2-stem mode is faster than 4-stem; suitable for real-time turnaround on single files.
• GPU (CUDA) gives 5–10× speedup. Check nvidia-smi for availability.
• Output is always 44.1 kHz WAV, matched to the input sample rate where possible.
• The accompaniment includes drums, bass, and all non-vocal elements mixed together.

Dependencies

Install via pipx install demucs. Requires PyTorch. Audio format support via ffmpeg.