What can Demucs (HTDemucs) separate, what can it not, and what are the practical artefact and licence considerations if I try to build an M&E or dialogue stem from a mixed track?

Problem: a dub or remix needs a music-and-effects (or dialogue) stem but only a final mix exists. Conditions: single mixed audio file. Method: the Demucs README describes a MUSIC source separation model that outputs four stereo 44.1 kHz stems: drums, bass, other, vocals (a --two-stems option gives e.g. vocals versus accompaniment); an experimental 6-source model adds guitar and piano. v4 is Hybrid Transformer Demucs, trained on MUSDB HQ plus an extra 800-song set, reporting 9.00 dB SDR on the MUSDB HQ test set. What it does not offer (inference from the stem list and training data): no dialogue / effects / ambience classes, so 'vocals' is a singing-voice target, not a speech-dialogue target, and film effects land in 'other' or leak into any stem; the README itself reports 'a lot of bleeding and artifacts' for the experimental piano source. Artefacts to plan for: output stems are auto-rescaled to avoid clipping, which can break relative volume between stems (use --clip-mode clamp or lower the input level), and stems are int16 unless --float32/--int24 is passed. Rights/maintenance: code and README state MIT licence; the repository says it is no longer maintained (a fork exists) and asks not to open feature requests. Practical implication: a separated 'other + drums + bass' sum is not a delivery-grade M&E; for a delivery use the original ProTools/DAW stems or have the M&E re-built; treat separation as a reference or rough-cut aid. Failure modes: phase/transient smearing and vocal remnants in the 'accompaniment'; level changes between stems. Limitations: README is undated; I did not run the model; weight-file licence is not separately stated in the README text I read. Curator correction 2026-10-23 (discovery audit record C3-B709-01; sources re-fetched 2026-10-23, excerpts re-located by curator GET): Problem. C3-B570-04 lists 'phase/transient smearing and vocal remnants in the accompaniment' under Failure modes without a label or a source. Conditions. Using Demucs for a stem from a mixed track. Method (correction). The Demucs README documents these artefacts: (1) output stems are auto-rescaled to avoid clipping, which can break relative volume between stems; (2) the experimental 6-source model shows 'a lot of bleeding and artifacts' for the piano source, with okay quality for guitar. It does not mention phase or transient smearing, nor vocal remnants in the accompaniment, for the standard 4-stem models. Treat those two as the earlier author's unlabelled domain expectation (plausible, unmeasured) rather than documented behaviour. Failure modes. Reporting undocumented artefacts as the README's. Limitations. README is undated; no model was run. Version/date. README main branch, fetched 2026-10-23. Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources. Limitations: Claims about what film dialogue/effects do under a music-trained separator are inference from the documented stem classes; no experiment was run. Quality is a MUSDB benchmark number, not a dialogue-extraction measure. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

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  "citations": [
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      "url": "https://raw.githubusercontent.com/facebookresearch/demucs/main/README.md",
      "note": "intro; Separation output; Maintenance note; Output clipping; LICENSE"
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      "url": "https://raw.githubusercontent.com/facebookresearch/demucs/main/LICENSE",
      "note": "intro; Separation output; Maintenance note; Output clipping; LICENSE"
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