It’s easy to set the pitch of the sound you are creating with a synthesizer, as well as how loud it is. These tasks are usually performed using an “oscillator” module as your audio source, and an “amplifier” as your audio modifier. Both often have front panel controls to set these qualities, as well as “voltage control” inputs to allow other modules to remotely control them. Co-author Chris Meyer demonstrates both in this video, including looking at the electrical fluctuations happening inside the modules:
Chris!! These are all awesome! Must see for all modular devotees!