Second and third columns are the same sound – the second one being the original mix beefed up exactly to the same RMS level as the final master. So comparing this to the final master (in the first column) reveals the tonal changes most objectively.
The better the mix, the slighter the changes are. If the mix is ideal, it could happen that there's not much to master at all. And remember: "better" does not mean "louder" - if you turn up the volume of "quiet" sound, it may sound punchier and more transparent than squeezed & limited "loud" master.
