Fourier

Based on an article by E. Muller in the January 1983 Elektor, in its Ejektor section: an imperfect but interesting idea that sounds wonderful, for shifting soundscapes and drones. It follows the basic principles of Fourier synthesis, with a bit of Walsh thrown in: sixteen pots, or the inputs beside them, control 7 sine and 8 cosine signals, supposedly harmonics of the initial signal, really stepped pulse waves. Fed a fast clock from a VCO (16 times the pitch to hear), a multiplexer scans the channels to the output; it is meant to go into a low pass filter. There are two multiplexers, run independently, or channel 2 gets a clock at half channel 1's rate; their outputs are available individually and mixed, with a pot setting channel 2's level as a sub-harmonic source, or an external signal mixed in instead. Each channel has its own reset and direction inputs. With a slow clock it becomes a strange sequencer. The pots are wired between +12 V and -12 V and are cut out when a signal is patched in: presets, not attenuators.

Key features

• Sixteen pots with an input and a bipolar LED each: S1 to S7, C1 to C8 and the channel 2 level
• CLK, RST and DIR inputs for each of the two multiplexers
• OUT 1, OUT 2 and OUT 1&2; MIX 1&2 takes an external signal in place of channel 2
• 24 HP; Nonlinearcircuits publishes no current draw, depth or assembled price (it sells the DIY PCB and panel), and ModularGrid lists none