I have a WiiM Mini and just tried Roomfit with it (it works on the Mini, too!).
When choosing the L/R option, my app does the sweep only on the left channel. The right channel plays only the "noise". The resulting adjustments are bad. I believe the L/R implementation, on the Mini at least, is bugged.
To clarify, this is what I hear during the measurements:
- Stereo Mode:
- Both channels play a sweep (no "noise")
- L/R Mode:
- Left channel
- Right channel
- "Noise" (sweep is skipped)
Does this match what the Ultra does?