How can I make a pulsing sound in MainStage?

In order to make a pulsing sound in MainStage, this can be approached in a few ways: either by using an LFO to modulate volume or filter cutoff- or by using the arpeggiator to create the pulsing arp.

Using the arpeggiator is a bit simpler:

1. Find a pad that has a similar character to what you're after, and then add an instance of the the Arpeggiator Midi FX plugin.
2. You could set the rate of the pulse timing (either 1/16 or 1/8 depending on your patches tempo).
3. In the Pattern tab, go into the Grid mode, select the little chord icon so that the arp plays the full chord, and set the range to just that chord.
4. Then, go into the options tab and adjust the length of the notes.

Here is a video that covers the Arpeggiator in depth: