Vector Delay's particle system relies on an Emitter to generate the particles that drive its modulation, and this bit breaks down the five controls that shape that behavior. Rate and Life set how often new particles appear and how long each one sticks around, while Voices caps the maximum number that can exist at once. Together these three controls determine the density of movement feeding your delay's modulation.
Mass and Random Mass round things out by setting the starting size of each particle and how much that size varies from one to the next. Since particle mass often gets mapped to affect things like pitch or feedback, dialing in Random Mass is a quick way to add subtle, organic variation to a delay pattern instead of a mechanically repeating one.