ACX mastering: getting files to pass
Mastering is the final technical step that brings edited audio inside the ACX window. This is the focus of the ACX audiobook mastering service.
The usual chain
Corrective equalization removes rumble and harshness, compression evens out the performance, and a limiter holds peaks under the ceiling while RMS is raised to target.
Chapter consistency
All files are mastered with matched settings so a listener hears the same tone and level from the opening credits to the last chapter.
Limits of mastering
Mastering raises noise along with the voice. A recording made in a loud room may pass loudness and still fail the noise floor, which is why clean recording matters.