Harmonyzer add several chord notes played on a dedicated split part of the keyboard ("left hand") to the solo notes played on the other split part ("right hand"). Each part can send its notes to a separate MIDI channel.
Insert it before one or more VST instruments, choose MIDI channels, split point, CC for enabling/disabling harmony effect and the maximum number of solo notes (incl. added chord notes).
Important: The Harmonyzer is a MIDI processing plugin only and has no internal tone generation.