The reflection of ultrasonic sound beams against the human body is used in this work to convert the position of human bodies into audible sound. In the vertex of an imaginary tetrahedron a frequency modulated ultrasound-emitter is placed and in its remaining corners three ultrasound-receivers are positioned to catch the emitted ultrasounds. If a human body moves in the imaginary tetrahedron each receiver will detect a different differential signal within the audible range. Every, relatively slow, body-movement causes a Doppler-shift of the sound produced by the ultrasound-emitter. As a result a pitch-shift is produced that is within the human audible range.  The position of the body determines the sound. If nobody is present in the scope of the imaginary tetrahedron, then no sound is audible. In the imaginary tetrahedron every movement, no matter how small, changes the pitch of the sound. In a newer version of Holosound, MIDI conversion was integrated so that a variety of sounds could be implemented. Holosound has been used as a musical instrument but it has also been presented as an interactive sound installation. 

Audio: Logos Duo (Godfried-Willem Raes & Moniek Darge), Holosound, performed at De IJsbreker, Amsterdam, the Netherlands, 29/12/1984