The composer and performer Godfried Willem Raes, founder of Logos – Belgian-based research and production centre for experimental music – is well known for his work as an instrument-maker: over a few decades he created a huge Robot Orchestra, combining experimental instrument design with several kinds of musical interfaces, such as wireless gesture control, real-time sound analysis, microwave radar, acceleration sensors, pyro detectors, light sensors, brainwaves, EEG and ECG, etc. Interestingly, his research has also been deeply committed to the study of piezoelectricity, focusing mostly on the use of piezoelectric elements in Ultrasound systems, although he also realized many works using piezoelectric microphones to amplify objects. Since the mid-'60s he started experimenting and researching on piezoelectric materials, with piezo elements such as seignette salt, a very hygroscopic material that deteriorates rapidly with humidity, used at an early stage for contact microphones, cheap headphones, crystal radios. Already from his childhood Raes got access to components coming from the research department at Philips, in Brussels, where a friend of his parents worked as engineer. At the end of the ‘70s, when piezo disks became available, he continued researching, making circuits to preamplify their signal, in order to correct their impedance and eliminate their resonant frequency. Raes collected also many books with data about piezoceramic materials, while contacting factories that produced piezo. Since the mid-'70s, Raes started exploiting piezos in his artistic projects with ultrasound, working especially in the range between 20kHz and 70kHz. He started then to build piezoelectric-based systems acting as gesture sensors, using them for reflection and for measuring people's movements as radar devices, in a doppler setting. Early in the '80s, one of his major results has been the Holosound production, which exists both as performance, as installation, and as concert version. The main idea of this work relies on translating the movements of the performer, or of the audience, into sounds within a dynamic multi-dimensional system. A frequency-modulated ultrasound emitter is placed in a specific point and directed towards (at least) three ultrasound receivers, placed on the four corners of an imaginary tetrahedron (all angles 60 degrees). From the receiver, the signal goes to a demodulation circuit to bring the signal back to the audio realm. The three signals from the ultrasound receivers are used also as inputs for special magnetic transducers connected to a given set of changeable objects (e.g. long springs and metal chimes up to three meters) inducing them to vibrate. In installations more receivers can be used, all related to the same ultrasound emitter (a Holosound component is shown in fig. 1.6.1). Objects such as keys, or broken glasses, can become audio sources: since their frequency spectrum is rich in many inaudible ultrasounds, little movements such as touching the keys produce strange noises, due to the fact that the system allows the translation of these ultra-high frequencies into the audio realm. Raes used piezoelectric technology in many other projects in a very creative way. In his early work, he built, for example, a monochord in which he used both an electromagnetic transducer and two piezos in order to amplify the string.
Fig.1.6.1. Holosound component: four piezos encapsulated in silicon with preamplifier in the black box.
Between the '60s and the '80s Raes' work was deeply connected with the experimental music scene: at Logos, in Ghent, he hosted the most relevant experiences of that time, getting in touch with many interesting musicians, such as Richard Lerman and Hugh Davies. Raes still owns an original Hugh Davies Springboard, bought from the English composer in 1974 (fig.1.6.3).
The choice of using two diverse types of microphone is based on the possibility of exploiting their different properties: the electromagnetic microphone works better for the bass frequencies, while the piezos are very good for scratching sounds, and for high sounds in general. So the monochord has two outputs: one for the two piezos - that are mixed internally - the other for the microphone with the magnetic transducer, which comes from an electric guitar (fig.1.6.2). The two pre-amps are contained in two different circuits - one for the piezo and one for the magnetic transducer, and the two signals are then mixed externally.
see also APPENDIX 3 (Interview with Godfried Willem-Raes), or >> go to 1.7 Mikrophonie I by Karlheinz Stockhausen and the Feedback Studio
