Where are these RMS/Noise Floor numbers located?

ACX Check.

You don’t have to do it that way, but it’s the most convenient. There are ways to fake out the noise measurement in that tool, but overall, it works pretty well.

We published an audiobook mastering process.

https://forum.audacityteam.org/t/audiobook-mastering-version-4/45908/1

It’s “RMS”. Root Mean Square. It’s a formal electrical engineering measurement that just happens to work out to loudness. So the three audiobook technical measurements are loudness, peak distortion and background noise.

We do warn you after all this you still have to know how to read aloud. There’s no tools to correct that.

Let us know if you get stuck.

Koz