  This paper describes the process of developing a shared instrument for
music-dance performance, with a particular focus on exploring the boundaries
between standstill vs motion, and silence vs sound. The piece Vrengt grew from
the idea of enabling a true partnership between a musician and a dancer,
developing an instrument that would allow for active co-performance. Using a
participatory design approach, we worked with sonification as a tool for
systematically exploring the dancer's bodily expressions. The exploration used
a "spatiotemporal matrix", with a particular focus on sonic microinteraction.
In the final performance, two Myo armbands were used for capturing muscle
activity of the arm and leg of the dancer, together with a wireless headset
microphone capturing the sound of breathing. In the paper we reflect on
multi-user instrument paradigms, discuss our approach to creating a shared
instrument using sonification as a tool for the sound design, and reflect on
the performers' subjective evaluation of the instrument.
