No offense, bandcoach, but the sound is too pumpy to just be mute automation. It sounds like a very long oscillating pad patch (probably just one note being played, but it might be multiple notes to create the "chord change effect")with what sounds more like a gate. Probably being fed via sidechain from an arpeggiated sound of some sort (no way to tell what sort of sound is feeding the gate via sidechain, and honestly is doesn't matter - gates just look for signal, not tone or pitch or anything). I would say that's how they are doing it. By using the attack and release settings of the gate, you can adjust how "pumpy" this arpeggiated mute effect sounds.