Must Pass follows the evolution of a harmonized whole-tone melody through a half-hour scored "thunderstorm." Calculated at performance time using a Gaussian event distribution, this "storm" is composed of over 30,000 individual raindrops and hundreds of thunderclaps. Each drop has uniquely controllable parameters for duration, volume, pitch, and pitch discernibility.
The melody and initial pitch were triggered by the impact of rocks thrown into a bucket of water, as measured by a submerged hydrophone. Decisions as to the size of rock, when to throw, and how hard to throw were made during the performance while watching the dancers on stage. At the beginning, the timing of the notes is erratic and unpredictable. As the storm subsides, the notes become more lyric and regular. As the storm progresses, the possibility for harmonization via chords increases.