Since the Shuttle Control is only able to handle one device at its ‘to host’ jack, there always was the question how to connect a few devices that simultaneously deliver clock and MIDI data (e.g. drum machine, USB or USB-MIDI keyboard/controller) to that port. Shuttle Mate is the solution.
The signal at the DIN MIDI In DIN socket is immediately returned via the DIN MIDI Thru socket. The MIDI In is merged with the USB MIDI signal and are available simultaneously at the other USB socket and the DIN MIDI Out.
The inbound and outbound USB connectors are both bi-directional I/Os, yet only outbound supports +5V USB power. The power source can be your computer, the Shuttle Control etc.
You might as well use the Shuttle Mate for simple conversion from USB MIDI to DIN Output.