What changed becomes its own waveform. The diff slot is a virtual slot that plays back the A − X residual, the sample-by-sample subtraction of the active version from the reference. Once level and timing are matched, everything the two versions share cancels to silence, and what's left is the change itself. You route that residual through the same waveform, spectrogram, and export paths as any other slot, so you can see where in the file the difference lives and how loud it is, not just hear that something moved.
Polarity matters for the subtraction. Each slot has a ϕ toggle that flips polarity, useful for catching a wiring error, and for diff work where flipping one signal is what makes the residual sit closer to zero. The diff slot recomputes automatically (80 ms debounced) whenever nudge, gain, polarity, or level-match changes, so the residual always reflects your current alignment. It has no live measurement of its own, switching to a diff slot clears the live loudness and stereo displays, because the diff buffer plays pre-computed.
Or overlay instead of subtract. The Waveform A overlay toggle draws slot A's waveform as a ghost behind whichever slot is active, a direct visual A/B at the sample level without leaving the active version. And the Compare metrics popover puts every loaded slot side by side in one table: integrated LUFS, true peak, sample peak, LRA, DR, speech stats. Read the numbers and hear the residual, from the same comparison.
