A preset is like a snapshot of the faders. The opposite realtion holds for negative values. 0 is no modulation. These parameters determine the duration of grains. Generally, grains are too short to exhibit any inner structure, i.e. shorter than 20 ms.
Long grains are computation intensive.
Increasing this value by 12 will double the duration fix value. Increasing this value by 12 will double the duration random deviation range value. This parameter determines the extent of spreading. Increasing this value by 12 will double the duration spreading factor. If positive value are given, loud parts will be played back with longer grains and low parts will be played back with shorter grains.