signal. There are no physical devices connected to the virtual fader because it is simply more like a plus or minus button on a calculator than a fader. It just looks like a fader in order to be familiar and consistent to other aspects of the audio recording world.
Voltage Control Amplifiers are different than standard faders because they do not pass an audio signal through them. They can be assigned to control other faders, groups or function that do pass audio. VCAs are commonly used to control all of the faders of a group simultaneously on analog consoles and in most DAW programs, but are also seen assignable to a myriad of functions in analog and software synthesizers.
There are other types of faders that you may hear about like moving faders, flying faders or motorized faders. These are all similar in that they are physical faders on an analog or digital console that can be moved by motors into a specific position.