Ableton's official Learn Live series walks through the core sample playback controls in Vector Grain, the granular looper and polyphonic sampler introduced in Live 11. In MIDI Mode, incoming notes trigger a looping section of the loaded sample, and this bit covers the parameters that shape exactly how that loop behaves.
Start sets where in the sample playback begins, and Size controls the length of the looped region, either in milliseconds or synced to note values. The Fade control shapes the loop's envelope: panning it left applies a fade-out, panning it right applies a fade-in. Reverse playback is also available, along with a multimode Filter for further tonal shaping.