xpSpeed changes the speed of particles passing through it.

Object Properties

Object tab menu for xpSpeed.

Enabled

Checking this box activates xpSpeed.

Mode

Set at Independent, by default.

You can change this to Action-Controlled.

Independent Mode

In this mode, particles will be affected if they come into the field of effect of the modifier.

Action-Controlled Mode

When in the Action-Controlled Mode setting, the modifier will only act on a particle when told to do so by an action.

Operation

Set as Incremental, by default.

The other settings are: Use Spline, Absolute and Acceleration.

Incremental