AU4 transforms ambiance-noise to  sounds.

A resonance-chamber receives sound waves and passes them on to 2 strings. An electro-magnetic pickup converted the string-vibrations into electric signals. The signals are amplified and passed on to a line-out, where headphones and recording-devices can be plugged in.

AU4 is specially designed for operations in parks and green areas (e.g. at the side of roads).