MIDI Monitor The MIDI Monitor window is a graphic display of data transmission activity on the Printer and Modem ports; use the MIDI Monitor dialog box to quickly see if ports are sending and receiving data. Each port shows an In and an Out graphic display represented by rectangular bars. When data is being transmitted or received on a port, the bar becomes filled in. Ports that are transmitting or receiving data are checked in the Activity boxes. MIDI Monitor is not accessible under OS X or under OS 9 if OMS is installed. Use OMS Setup under OS 9 instead. See Also: Ports OMS MIDI Setup