check out the clips on zvex seek wah, ooh wah, moog murf
it kinda like a tremolo, except that its not presenting the signal as uniform chop up/swelling in out kinda sound, but rhythmic patterns with different time interval as if the sound is fed thru series of filter, each with different setting and distant apart from each other
if a guitar signal going thru a tremolo sounds like 'djeng-djeng-djeng-djeng djeng-djeng", with equal time interval between each djeng, an arpeggiator will sounds like "djeng-djongdjing----djengdjeng-djingdjongdjing--djong dong dting dtang-djengdjeng-djongddong---djeng
the repeats can sound different from each other with different time interval between each repeat to make up certain rhythmic pattern kinda