A standard rudiment in percussion, from which hundreds of variants have sprung.

A double-stroke roll incorporates bouncing the stick twice with each hand before alternating, and doing so in a clearly rhythmical and controlled manner. A double-stroke roll's pulse is always locked into some sort of meter or tempo, as it were.

A common percussion exercise to teach double-stroke roll timing:

R  L  R  L  |  RR  LL  RR  LL  ||
1  +  2  +  |  1   +   2   +   ||

This is also commonly found in groupings of sixteenth notes, not just eighth notes.