There are many schools of thought on the proper way to play a snare drum roll. I play with a controlled bounce every time. For march-like tempos, my roll base is 16th-notes. I use three bounces on each 16th-note as my buzz at this speed. Playing less than three bounces is not a sustained sound. Playing more than three bounces results in a choked tone.
For softer playing, the roll base decreases while the number of bounces increases to make up for the increased space between notes. The slower roll base makes the roll softer and adds a sense of calm to the energy of the roll. My soft dynamics require five bounces per buzz.
The quality of the buzz remains the same no matter the tempo or dynamic. The only difference is the amount of time the bead is allowed to stay on the head. More time on the head, more bounces. Less time on the head, less bounces.
The first of the following exercises begins by developing this buzz control. The second exercise demonstrates control of similar bounces no matter the rhythm.