"Echoic Defiance of Gravity" is a visual music piece featuring "Bouncy Echo"—a virtual audiovisual instrument based on a computer simulation of the motion of bouncing balls, showcasing its potential as a versatile, expressive tool for real-time music performance. Here, the simulation not only governs the motion of the balls in the visual domain but also determines the musical outcome of the piece in the auditory domain, thereby providing a unique cross-modal experience for both the audience and the performer. In addition to the fact that this piece may invoke intriguing discussions in terms of simulation-based algorithmic composition, it is especially noteworthy that it is a unique amalgamation of a fixed, deterministic set of musical notes and partly uncertain, indeterministic follow-ups generated by computer simulation in the visual domain. Although the exact time and the frequency of occurrence of musical events are chance-based and effectively random, they are perfectly relevant to the motion of the ball presented simultaneously. Regarding the musical organization of the piece, the artists focus on exploring a wide range of parameter combinations, keep evaluating the musical versatility of the system employed, and hope to bring more unique outcomes to the stage at the conference than those featured in the accompanying video.