Not 100% sure, but I think SMP BIAB uses a custom version of DEMUCS for stem separation, whereas BIAB uses Zplane's Stems Pro, which I suspect it's a fork from the original, open source project, Spleeter.

Nowadays, there are only a very small handful of stem separation algorithm, and every program on the market offering that feature use one of them (sometimes, a customized version).

The point is that currently, no stem separation model is perfect, all of them depend on the dataset they have been trained with, so, for certain songs one algorithm may work better than other, and viceversa. If you find a song where your preferred program fails to separate the track you need, just try another model, you may be luckier (or not). It's just the way it currently works.


Latest BIAB version, latest build.