Computer organ tone input for alterable stops is achieved by single-key input through a decoded keyboard which is couple to a logic network and optoelectrical output drive circuitry. The decoder circuitry activates selected optical emitters in an array which is mounted in the optical reader of a computer organ such that the decoder circuitry is electronically isolated from the computer organ. The invention eliminates the need for a tone card library, does not interfere with the sensitive circuitry of the organ and permits instantaneous reprogramming of alterable voices.