HTDemucs GGUF

Meta's Hybrid Transformer Demucs (v4) converted to GGUF for stems.cpp, a C++/ggml stem separator that runs on CPU, CUDA, Vulkan and Metal with no Python. The three published HTDemucs models are here:

Download and run

git clone --recursive https://github.com/betweentwomidnights/stems.cpp && cd stems.cpp
./build.sh vulkan                   # or cpu | cuda | metal   (Windows: build.cmd)
./models.sh htdemucs_6s             # F32; --encoding f16 for the smaller files
build-vulkan/bin/stems-split -m models/htdemucs_6s-27M-v1.0-F32.gguf -i song.wav -o stems/

stems-server finds these files by model name ("model": "htdemucs_6s"); see the stems.cpp README.

Parity with PyTorch

Each figure is the SNR of the C++ output against demucs 4.0.1 in float32, full separation of a 20 s clip (demucs' test.mp3), for the worst stem of each model. Every stem of every model passes stems.cpp's parity check (cosine 0.9999 or better). Measured 2026-10-02/03 on stems.cpp with ggml f30f0cdc. CPU, CUDA and Vulkan: Core Ultra 9 275HX / RTX 5070 Laptop. Metal: Apple M4, against torch refs dumped on the M4.

F32 is the reference. F16 stores only the cross-transformer's matmul weights in half precision, with the convolutions kept F32. It costs about 20 dB on CPU and Vulkan and nothing measurable on CUDA (whose F32 matmuls already run as TF32), and stays more than 50 dB below every stem. It is about 40% smaller, not faster. The per-stem tables are in stems.cpp's docs/PARITY.md.

Sources and license

• Upstream: facebookresearch/demucs, demucs 4.0.1. Checkpoints: htdemucs 955717e8-8726e21a.th; htdemucs_6s 5c90dfd2-34c22ccb.th; htdemucs_ft f7e0c4bc-ba3fe64a.th, d12395a8-e57c48e6.th, 92cfc3b6-ef3bcb9c.th, 04573f0d-f3cf25b2.th.
• Converted with stems.cpp's tools/convert_htdemucs.py. Tensors are renamed, packed attention projections are split into q/k/v, constants are folded into metadata, and the F16 files halve the transformer's matmul weights. The architecture and weights are otherwise unchanged; every GGUF records its upstream checkpoint in general.source.file.
• Code and weights are MIT-licensed by Meta Platforms, Inc. and affiliates; see LICENSE and NOTICE. SHA256SUMS lists every GGUF.

If you use HTDemucs, cite Hybrid Transformers for Music Source Separation (Rouard, Massa, Défossez, ICASSP 2023).