Low room tone noise

A word on using Analyze > Plot Spectrum. It has the annoying habit of changing loudness references on the left to be most helpful to you, in its opinion. The numbers on the left move. It would be as if your speedometer needle stays in one place and the car moves the numbers in a circle.

Anyway, see at around 100Hz, there is a tiny purple spike that goes up to about -78dB? If you run Low Rolloff and then analyze again, the spike will still be at about -78dB. But -78dB is now at the top of the chart.

If you’re not paying attention…

Oh, by the way, yes the ACX audiobook noise limit is -60dB, but as a practical matter, you have to actually hit -65dB or quieter to safely submit. Your work without the Noise Reduction comes in about -63dB or so. Yeah, technically it does pass… But…

https://forum.audacityteam.org/t/audiobook-mastering-version-4/45908/68

Koz