The realtime separation engine takes 5–15 seconds to load after you select a realtime quality (longer on older machines). Until it’s ready, ReStem passes your audio through untouched — so if you hit play immediately, it can look like nothing is happening. Give it a moment; the display shows when separation is live.
If it never engages:
- check that your buffer size is reasonable (1024 or less),
- confirm your Mac DAW isn’t running under Rosetta,
- and post your machine specs here — realtime needs a reasonably modern CPU, and on Windows ReStem tunes itself to your machine on first use.