One voltage might control the pitch, another the timbre, and a third the amplitude. The signals between the modules were all analog, using voltages to represent musical parameters. Even today, the configuration for a sound on a synthesizer is called a patch, though it might not involve any cables or plugs. On these systems, the configuration of the patch cables, knobs, and switches determined what sort of sound was created.
The Moog System 35 Modular Synthesizer (Photo Courtesy Moog Music)
