MM-RT is a tabletop tangible musical interface that employs electromagnetic actuators and small permanent magnets to physically induce sounds on objects. When, for example, a box with permanent magnets inside is placed on top of a pad, an electromagnet installed below the pad actuates the permanent magnets, causing them to bounce and hit the walls of a box. Timbre generation on each box is physically and digitally constrained: Each object comprises different materials and size, and a granular synthesis technique (a digital form of time domain additive synthesis) is used to create the sound producing mechanism.