Ableton's own Learn Live series walks through the four core grain-playback controls in Granulator III's Classic mode, building a clear picture of how each parameter shapes the fundamental texture of a granular sound.
Position sets where in the loaded sample the grains are read from, and you can adjust it by dragging directly in the waveform display. Grain Size controls how much of the sample is captured in each grain, and because playback speed is tied to pitch, it's more accurate to think of it as a window into the sample rather than a duration.
Scan causes the playback position to drift forward through the sample while a note is held, turning a static texture into something that evolves over time. Shape sets the amplitude envelope of each grain: at 50 you get a smooth fade in and out, at 0 a sharp attack with quick decay, and at 100 a slow attack that cuts off abruptly.
Together these four controls define the core character of any granular patch in Granulator III, and understanding what each one does independently makes it much easier to dial in the texture you're actually after.