I use the MOTU MicroExpress USB MIDI Interface with my G4. They also make a smaller bus-powered one, called the FastLane, also USB. It's better not to use them with a USB hub, or at least to do a search to find the best hub to use if you must. The MicroExpress interface has a 1/4" jack for Timecode input, if you need that, but the FastLane doesn't.