A man's voice, i.e. of him but now before mentioned, namely, Christ. To understand the vision, i.e. by declaring it more plainly to him: this shows Christ to be God, in commanding and sending his angel. Gabriel signifies the strength of God.
Related Commentaries of Daniel 8:16
Daniel 8:16
16 And I heard a man's voice between the banks of Ulai, which called, and said, Gabriel, make this man to understand the vision.