Derek Holzer > TONEWHEELS @ STEIM, Feb 2008

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In late February of 2008, I came to STEIM to perform the audiovisual performance TONEWHEELS (along with Dutch graphic designer Sara Kolster), and to work on some specific hardware issues I was having with the equipment I’ve been developing for the performance.

About TONEWHEELS:

TONEWHEELS is an experiment in converting graphical imagery to sound, inspired by some of the pioneering 20th Century electronic music inventions. Transparent tonewheels with repeating patterns are spun over light-sensitive electronic circuitry to produce sound and light pulsations and textures, while projected graphical loops and textures add richness to the visual environment. This all-analog set is performed entirely live without the use of computers, using only overhead projectors as light source, performance interface and audience display. In this way, TONEWHEELS aims to open up the “black box” of electronic music and video by exposing the working processes of the performance for the audience to see.

Tonewheels website

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Essentially, the TONEWHEELS performance works as shown above. Voltage is sent to a phototransistor, which is illuminated from above by the halogen bulb of an overhead projector. Small transparent “tonewheels”, each with a different pattern printed on them, are spin by small motors over the phototransistors, which causes the voltage going through them to be modulated. The output of the phototransistors can be connected directly to a speaker (as shown above), however most often I run them into the line-level channels of a mixer.

The first standalone box I built to send voltage to the phototransistors used a 7805 voltage regulator to keep the current to all the phototransistors stable:

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This system worked quite well when run into the line-level inputs of a mixer, however I failed to get sound when using the microphone inputs of the mixer. Also, I wanted to experiment with sending the voltage to a number of commercial and self-built modules in my Doepfer analog synthesizer. After doing some research, I came up with the following design, which was completed during my STEIM residency:

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This design formed the basis of a Doepfer-compatible module capable of sending voltage from a single 7805 regulator to 8 phototransistors. The voltage returning from the phototransistors is buffered by a TL072 dual op amp. The first channel of the op amp provides a low impedance, inverting amplifier, which is followed by another inverting amplifier to bring the voltage which comes out back into the positive range. A single non-inverting amp was also tested, however it presented too high an input impedance to be useful. Earlier versions of this design left out the 7805 regulator, causing a very high amount of crosstalk between the 8 channels and basically proving that a regulated voltage supply is necessary for the circuit to function in a multichannel setup. The output of this circuit can be sent to either a line or microphone level input on an audio mixer, or to any of the modules in my Doepfer synthesizer.

Some other modules I built for the Doepfer to use with this circuit include Harry Bissel’s Morph-Lag circuit, which I found very useful when using the phototransistors with a slow-moving tonewheel as a kind of LFO to modulate the gain of another channel, the cutoff of a filter, etc etc, and Jim Patchell’s Control Voltage Processor, which can adjust the gain and offset of the signal when I wish to use it as a control voltage in the modular. I also built four digital delays around the PT2399 delay IC, using the Tonepad Rebote 2.5 delay PCB design.

The work that I’ve done so far on this project has largely been towards presenting it as a performance. With all the basic development finished, the next stages will be to create a workshop format around this very simple technology, where participants can make their own TONEWHEELS circuits. The first such workshop will take place at the end of May, during the “Waves” exhibition, organized by HMKV at the Phoenix Halle in Dortmund. Installation versions of the project remain a possibility as well. I will also be expanding the technical information posted on line in the TECHNICAL section of the TONEWHEELS website.

In addition to the time and space provided by STEIM, the following institutions, groups and individuals were very helpful in designing this system, and I would like to thank them here:

The Synth DIY mailing list

Carsten Seiffarth & Tesla (Berlin)

Jeff Mann (Berlin)

Martin Howse (Berlin)

Manfred Fox (Berlin)

Marc Boon (Amsterdam)

Ralph Schreiber, Christian Faubel and Tina Tongerel (Cologne)

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