Final password:
Hold Down + Select and press Up, Up, Down, Down, Left, Right, Left, Right, II, I, II, I at the Human opening screen.

Sound test 1:
Hold Down + Select and press Left, Right, Down, Up, II, II, II at the Human opening screen.

Sound test 2:
Hold Down + Select and press I, II, I, I at the Human opening screen.

Sound test 3:
Hold Down + Select and press Down, Down, Up, Up, II, I, II, I at the Human opening screen.

Sound test 4:
Hold Down + Select and press I, II, Up, Down, Left, I, I at the Human opening screen.