GrainField is a performance for solo performer and an unlimited number of players in the audience who participate through their mobile devices. In this performance, the sound produced by the improvising performer (e.g. a percussionist, beatboxer or singer) is recorded via a microphone and sent in segments of a few seconds to the mobile devices of the players. Controlling a granular synthesis engine, the participants perform with a segment of sound by tilting their mobile device. The players’ sounds change asynchronously and smoothly at different phases of the recording cycle of around 20 seconds. The resulting soundfield is perceived as a diffuse granular echo or resonance of the performer. The performance is an exercise of collective improvisation that is nourished by the mutual listening of the solo performer and the players in the audience.