The single stroke roll is just R L R L R L R L — alternating, evenly spaced. There's nothing easier to describe and almost nothing harder to play perfectly even. Two key ideas: every stroke at the same volume, and your hands at exactly the same height.
Build speed by adding density (more notes per beat), not by rushing the hands. Quarter → eighth → sixteenth, each at the same tempo. Your hands learn the motion at the slow density, then carry it into the fast one.
The Weak-Hand Problem
Record ten seconds of your 16th-note singles and listen with your eyes closed. Almost everyone hears the same thing: the dominant hand slightly louder, the weak hand slightly lower in stick height, and a faint gallop where evenness should be. The fix is boring and effective — lead with the weak hand for a full practice block, and watch the stick heights in a mirror until they match.
Two minutes of truly even singles at ♩=80 beats twenty minutes of fast, lumpy ones. Speed comes from evenness, because an even roll has no hitches for tension to hide in. When the accented exercise feels effortless, that's your cue to raise the tempo, and not before.