We present a set of interaction techniques for electronic musical performance using a tabletop tangible interface. Our system, the Audiopad, tracks the positions of objects on a tabletop surface and translates their motions into commands for a musical synthesizer. We developed and refined these interaction techniques through an iterative design process, in which new interaction techniques were periodically evaluated through performances and gallery installations. Based on our experience refining the design of this system, we conclude that tabletop interfaces intended for collaborative use should use interaction techniques designed to be legible to onlookers. We also conclude that these interfaces should allow users to spatially reconfigure the objects in the interface in ways that are personally meaningful. Categories and Subject Descriptors H.5.2 [User Interfaces]: interaction styles, input devices and strategies J.5: [Arts and Humanities]: performing arts General Terms Performanc...