Why the room matters more than the mic
ACX requires a noise floor below -60 dB RMS — a genuinely quiet room by home-recording standards, and one that a better microphone alone won't get you to. A modest mic in a well-treated small space consistently beats an expensive mic in an untreated one.
Setting up a quiet space
- A small, soft-furnished room usually beats a large one — a closet full of clothes is a genuinely good vocal booth.
- Curtains, rugs and soft furniture on hard walls cut both noise and reflections.
- Pick one space and use it for the whole book. ACX checks that files match each other, not just that each one individually passes.
Keep mic distance and gain identical every session
The single most common cause of file-matching rejections isn't noise — it's inconsistency. A slightly different distance from the mic or a nudged gain knob between sessions changes both your recorded level and your apparent noise floor, even in the same room with the same equipment. Mark your mic stand position and gain setting so every session starts identical.
Record room tone on purpose
Grab several seconds of genuine silence — mic live, nobody speaking — at the start of every session. ACX expects a short stretch of room tone at the head and tail of each file, and digital silence sounds noticeably wrong to a listener where honest room tone doesn't. It also gives noise reduction a clean, accurate profile to work from if you need it.
A basic session checklist
- Same room, same mic distance, same gain as last session.
- Record several seconds of room tone before you start reading.
- Watch your levels while recording — fixing a clipped take afterwards isn't possible.
- One file per chapter, with the chapter title spoken at the start.
- Listen back to a section before moving on to the next session.
Getting the rest of the way there
Optivox's Audiobook mode masters specifically to ACX's targets — RMS window, true peak ceiling and room tone preserved rather than gated into silence. Upload a chapter, download the master and run it through ACX's own checker before submitting the full book.