Now that we know the difference between audio signals and MIDI signals, let's talk about the other kind of signal that Reason uses extensively: control voltage. Control voltage (CV) is an electronics term that refers to the way synthesizers communicated in the days before MIDI and computer technology.
Before computers and digital language, synthesizers used electronic control voltages to relay anything from knob movements to "note on" and "note off" messages. Synthesizers were well established when computers arrived, so the new digital instruments were designed to fit the established electronic conventions.
As you start working with synthesizers, you'll become familiar with lots of electronic synth terms, such as envelope, filter, resonance, LFO, and others.