Getting Noise Floor To -60 dB in Audacity

ACX Technical limits:
— Peaks no louder than -3dB.
— RMS (performance loudness) between -18dB and -23dB.
— Noise no louder than -60dB.

much to my surprise, I found that the noisy (to my ear) refrigerator in the next room (which I customarily turn off while recording) did not increase the noise floor while running.

How are you listening? Sometimes not hearing something is because your speakers or headphones can’t do it. I have a good quality music speaker system and I regularly hear problems that go right by most people. I have a silly joke that if you can hold your speakers in one hand, they’re probably not going to work particularly well.
Publishing companies regularly forbid the use of post production filtering. I suspect this is not so much because it’s a bad idea, it’s because most performers do it wrong. I should have saved it; one new reader arrived with a long list of effects and processing that they assumed were required to read for audiobooks.

No, not really.

On the other hand, if not for gentle equalization and noise reduction, there would only be four people reading audiobooks.

I subjected your clip to AudioBook Mastering and it passed ACX with no further work or noise reduction. First three sentences and declaration 2/3 down.
Screen Shot 2018-06-03 at 6.28.38.png

Only the first step, equalization did anything significant. Your raw clip is remarkably close. The clip has sub-audible noise which mostly vanishes with Low Rolloff equalization (click the graphics).

That spike at 89Hz may be your computer fan or fridge. It’s not a normal house power problem

So I think you’re done. This is the writeup for Audiobook Mastering 4.

The equalization step suppresses rumble and earthquake noises, RMS Normalization step sets loudness and Limiter sets peak/overload. If you read in a quiet environment, you’re done.

ACX Check has one oddity that can cause you to have bad readings. It needs to have at least a half-second of Room Tone (shut up and freeze) somewhere in the performance to read properly. Room Tone is built into the ACX submission format and it may be there for Voice Bunny, too.

Does Voice Bunny have provision to submit a test? I haven’t checked ACX, but they used to make you go through much of the production before they would tell you the quality was trash.