For those of you who might not know exactly what velocities are, they're essentially volume settings for each beat in Roc. They can add an extra layer of dimension to your loop by accentuating beats or muting them. You can access the velocity editor by clicking on the Velocity Mode button at the top of the application, and then set individual velocities by dragging up or down on the blue bars.
There are also some useful features in the Velocities menu under track options, which you can find by clicking on the small circle in the top left corner of any Roc track.
Reset Velocities - Sets the velocities for all beats in a track to their default level of 75.
Randomize Velocities - Sets a random velocity for each beat in a track. This is a great way to add dynamics.