The first set of stems screeched. The separator's math was fine, but the GPU copy of the program had been compiled 17 minutes before a bug fix and never rebuilt. The switch above plays both versions.
Add the four stems together and they should rebuild the song. Broken: they barely do. Fixed: they do, apart from 3 quiet seconds of intro.
Bass lives in the low end. Most of the broken bass stem was high-pitched noise, and that's what the screech was.
On the P4000 GPU, all three HTDemucs models match the original PyTorch model to seven decimal places. This 4:49 track took 4:42 with the four-model FT ensemble.
The transformer's positional embeddings are uploaded to the GPU before each segment. An early version uploaded them once, so from the second segment on they were overwritten scratch memory. That was fixed in the source, and the CPU build was rebuilt, but the separate CUDA build directory was not. The single-segment test still passed, because the bug only appears from segment two onward. Only the whole-song test catches it. build.sh now warns when another build is older than the source.