Hey there,
If your keyboard has a USB MIDI port, you likely will need something in the middle, like a computer, to create a MIDI network of sorts so your keyboard can control the BeatBuddy. You could possibly try a USB to MIDI cable coming out of your keyboard into the BeatBuddy but I am not sure this will work.
If your keyboard has 5 pin midi outs, just connect the MIDI Out of the keyboard into the MIDI in port of the MIDI Sync Cable.
Our MIDI Maestro Manual has a very informative MIDI basics section
Feel free to contact support@singularsound.com for more assistance!