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Grant Richter's Electro Optical Mixer
Voltage Controlled Electro-Optical Mixer
This text and the schematics were taken from the old Wiard DIY pages. This module was described as Exquisite Corpse / Cadavre Exquis, inspired by the surrealist game.
A simple and inexpensive device is described which allows selecting and mixing audio channels by control voltage. The circuit takes advantage of the low self-noise of analog photocouplers. The slow response time of the phosphour is used to integrate the pulse width modulated LED drive. Channel crossfading is accomplished by adding a "dither" signal to the comparator string, producing apparent linear crossfades between audio channels.