An instrument in which an acoustic or otherwise measurable disturbance or change is made in physical matter is disclosed. In one embodiment an oscillatory vortex shedding phenomenon is formed in water, in association with each of a plurality of finger holes. Water flows past a branch point where it can either flow over a labium, edge or the like in a resonant pipe, or out a finger hole, the finger hole being the path of lesser resistance to the water. Obstruction of the finger hole forces the water past an underwater sound production mechanism. Blocking water from coming out of a given hole produces a given note, which, in some embodiments, is electrically amplified by a hydrophone. In one embodiment there is a further processing of each hydrophone signal. Embodiments with various kinds of acoustic or optical pickups are also disclosed.