 The MIDI specification provides for a ground "wire" and a braid or foil shield, connected on pin 2, protecting the two signal-carrying conductors on pins 4 and 5.Although the MIDI cable is supposed to connect pin 2 and the braid or foil shield to chassis ground, it should do so only at the MIDI out port; the MIDI in port should leave pin 2 unconnected and isolated.Some large manufacturers of MIDI devices use modified MIDI in-only DIN 5-pin sockets with the metallic conductors intentionally omitted at pin positions 1, 2, and 3 so that the maximum voltage isolation is obtained.