- Real-Time Prototyping in Live Electronic Music:A Modular Crackle Instrument
During a visit to STEIM, the venerable institute of musical research in Amsterdam, I acquired several Crackle Boxes (Kraakdoos). This classic device, conceived by Michel Waisvisz with the assistance of Geert Hamelberg at STEIM in the mid-1970s, is a model of efficient and subversive design. A single op-amp, whose intended purpose is to amplify signals accurately, is configured in an unstable state, with its input, output and compensation pins brought out to six touch pads. The performer interacts with the instrument by bridging different points in the circuit with one's hands, eliciting noises that are sensitive to pressure, sweat and the declining health of the 9-volt battery powering it. Although built with limited resources— the touch pads are simply traces on the printed circuit board and the speaker is glued on—the Crackle Box is housed in an elegant wooden enclosure and succeeds in providing a tactile experience where most electronic instruments fail.
Despite the unpredictability of the Crackle Box, the range of its behavior is limited, making it wonderful as entertainment for dinner guests but less useful as a "serious" instrument. After I peeked under the hood (always the first thing to do when encountering a piece of equipment), the simplicity of the circuit reminded me of textbook exercises in electrical engineering, which I studied in college. My first thought was to extend the circuit by bridging two units together. I stretched resistors, capacitors and diodes resting on the touch pads across the boxes, altering circuit values and feeding the two amplifiers back into each other. While the sensitivity to touch remained, the boxes now possessed an expanded repertoire and became even more temperamental. It was also possible to configure the components' values to make noise without intervention by the hand, the sound shifting over time due either to instability of the circuit or the components being physically moved by the speakers' vibrations.
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I gave little more thought to the Crackle Boxes beyond those few afternoons of experimentation until I returned to STEIM for a residency in 2006. After deciding to scrap the project I had initially proposed due to its need for specialized parts, I remembered the ideas for a more configurable Crackle instrument (Fig. 10), which seemed appropriate to try out at STEIM. With the assistance of Jorgen Brinkman (who also assembled every one of the reissued Crackle Boxes), the new module was laid out and wired in a few days.
The design goals of the new unit were to make it compact, battery powered and absolutely flexible in routing while retaining the tactile interface of the original. I wanted four Crackle circuits that could function independently as well as work in parallel and feed back into each other, with individual speaker-driving outputs as well as a summed line-level output to interface with the rest of my analog electronics. Perhaps having another flashback to engineering lab work, I decided to use a trimmed down breadboard to expose the circuit guts to real-time manipulation. The breadboard is connected to six points of each Crackle circuit, functioning much like the patch bay of a recording studio. The circuit can now be altered easily during performance: its routings can be changed and multiplied; it can even receive external signal and control voltage injection. In performance, acoustic filtering is provided by different speakers connected to each output—high-frequency compression drivers, mini paper cones, piezo discs, etc., chosen for their limited bandwidth and other imperfections. These can also be easily positioned at different parts of the performance space to take advantage of resonant corners and provide some primitive spatialization.
In my mind, while this instrument obviously owes much to the original Crackle Box and Waisvisz's Crackle Synth, it is also a reduction of David Tudor-influenced electronics to the component level, manipulating frequency compensation cutoffs and gain values rather than gain blocks, phase shifters and filters. Although the outcome is laced with uncertainty, the visual simplicity and correspondence to what lies...