We have developed Audiopad, an interface for musical performance that aims to combine the modularity of knob-based controllers with the expressive character of multidimensional tracking interfaces. Audiopad uses a series of electromagnetically tracked objects called �pucks� as input devices. The performer assigns each puck to a set of samples that he wishes to control. Audiopad determines the position and orientation of these objects on a tabletop surface and maps this data into musical cues such as volume and effects parameters. Graphical information is projected onto the tabletop surface from above, so that information corresponding to a particular physical object on the table appears directly on and around the object. Our exploration suggests that this seamless coupling of physical input and graphical output can yield a musical interface that has great flexibility and expressive control.