VCA Faders
VCA stands for Voltage-Controlled Amplifier. VCA faders were originally found on hardware mixing desks. They allowed users to control the volume levels of several mixer channels with only one fader. To assign channel faders to a VCA fader, the respective channels must be physically connected with the VCA fader.
In Nuendo, the VCA fader function is based on the same concept. VCA faders can be connected with different types of audio-related channels. This allows the VCA faders to control the volume of the connected channels. A channel can be connected to only one VCA fader.
From a technical perspective, moving a VCA fader to a different dB level adds or subtracts the new value to or from the original values of the connected channels.
Example
A channel has a level of -6 dB, the VCA fader is at the 0 position. If you move the VCA fader to a level of +3 dB, this value is added to the level of the connected channel. The connected channel now has a level of -3 dB.