When using with the hand held, you better use an separate mic (e.g. your phone?!) and combine both streams in post rather than doing it with the cam. First, the USB port is not activated for external purposes as gwhuntoon said and the firmware does not give a clue how to enable it anyhow. Second, you will likely destroy your footage, when you connect anything to your cam while the gimbal is active, simply because it will be shaky when you move around and the gimbal tries to stabilize but can't as its tied.