Normally MIDI data arriving at the “MIDI in” port of some device is passed on to a through (thru) port of that device if one is available. This allows many devices to share a common MIDI bus. Only MIDI data created within that device is sent out of its MIDI out port. However, when MIDI Echo is enabled data arriving at the MIDI input is “echoed” back out of the MIDI output in addition to the thru port. This data may or may not be merged with other data generated by the device.