"Sonic beams / Acoustic shadows" is an improvised composition played on a non-contact haptic interface. The audio generation is based on a "no-input mixing board" concept. The primary feedback loops generated with the mixing board are projected through the PA system and at the same time they are used used to modulate (AM) an ultrasonic sinus carrier. The amplitude-modulated signal is driving an array of 97 ultrasonic transducers arranged on a spherically shaped surface, so that the acoustic radiation is focused at the sphere centre. The result is a relatively strong and spatio-temporally precise tactile reproduction of the projected audio signal. A simple ultrasonic receiver is used used to pick-up the sonic beam and is placed in front of the transducer array – 20cm behind the focal point. By moving his hand in the focal point region, the musician is acoustically shadowing the receiver. The signal which is picked up by the ultrasonic receiver is fed directly into the input of the same mixing board. When the musician is playing the instrument, i.e. moving his hand around the focal point of the ultrasonic beam, he is indirectly manipulating the intensity of the receivers output. This ultrasonic signal is generating turbulences in the primary oscillation circuit (audible frequencies) of the mixing board. As a result a wide variety of acoustic material can be generated, merely by positioning ones hand between the transducers and the receiver.

download - "An ultrasound based instrument generating audible and tactile sound"
paper, published at NIME 2010 in Sydney, Australia – www.nime.org

download - "Tactile feedback based on acoustic pressure waves"
paper, published at ICMC 2010, in New York, USA - www.icmc2010.org