In percussion technique, a double stroke is two rapid taps in a row from one hand. The double stroke roll is two rapid taps from each hand consecutively, back and forth. This can yield a much faster speed than the single stroke roll, but only when done cleanly and correctly. Two problems have to be overcome. The weaker hand needs to be able to perform a double stroke roll as quickly as the dominant hand. Then, the second tap from each hand needs to sound just as strong as the first tap. While there are some tricks to be learned with sticks, the most important part of the technique is the raw ability to tap like a machine! The second pattern in Rudiment Rock-It develops this skill in a unique and entertaining way.
The game measures the amount of time taken between each tap. It then penalizes inconsistency by making the rocket off course. Going too far off course results in the rocket leaving the screen and the player loses. Also, the amount of displacement differs depending on whether the first or the second tap is being performed. Otherwise only the first tap from each hand would need to be consistent. The game forces the player to be steady all around.
As for the problem of the strength of each tap, the game keeps the player honest by touch screen limitations. If a tap isn’t strong enough it is generally because the stick or hand didn’t come far enough off of the drum to make a good sound. It’s the same when tapping a mobile device. If the player’s hand doesn’t get enough distance from the screen to detect a release, it will not respond the second time. The rocket will quickly begin to go off course. But the player has the opportunity to slow down and regroup before they lose entirely. This is extremely useful for getting overconfident students to slow down and practice correctly!