Can I use a USB MIDI keyboard?

No. It is not possible to connect a MIDI keyboard to the USB device insertion slot on this unit and play it.
There are two ways to use a keyboard with this unit:
1) Use a keyboard which has a DIN MIDI OUT port.
2) Connect your USB MIDI keyboard to your computer and connect the SP-16’s USB-B type terminal to the computer’s another USB port. You can play the keyboard using the SP-16’s MIDI IN feature by sending MIDI signals to the SP-16 via DAW application.