About The MIDI In Port The MIDI in plug can be used to interface another MIDI device to your PC, via the USB port. Data received from this device will be transmitted via the UC- 33 to the PC. This is achieved using a second USB MIDI out. So, when you select the MIDI devices section of your sequencer you will see two UC- 33 USB MIDI Ins. The first of these is used to receive the UC- 33 controller data, the second is used to receive data from the other device connected to the UC-33’s MIDI IN plug.