MainStage has one of the most powerful/easy to use arpeggiators on the market. Here’s how to add one to your channel strip: 

1. Open MainStage. Select a template. 

2. Click on a patch where you want to add an arpeggiator. 

3. Click on the blank space next to Midi FX, then select “arpeggiator” from the menu.

MainStage’s Arpeggiator plugin offers up, down, up/down, four variations, a 4-octave range, grid programming, chord arpeggiation, and a bunch more. Check out this tutorial to find out more.