Using mobile devices as instruments in computer music is one of the goals of the "Pure Data anywhere" project [5] . An obstacle we encounter is controllability, because most of the devices do not offer the necessary interface, such as MIDI or USB, in order to be controlled by external controllers. Also, attaching external controllers to the devices would make them less portable. This paper investigates the possibilities of using the touch screen, an interface that is part of mobile devices like

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... Personal Digital Assistants (PDA's). It describes usage scenarios that have been implemented for the PD anywhere system. As most traditional PDA applications use the touch screen in the same way as a mouse would be used, emphasis is put on the difference between mouse and touch screen interaction for instruments. We are going to describe interaction models, that were found useful and intuitive and enable the touch screen to become a fairly sophisticated controller for expressive real time music on a PDA.