The room has a say in things
ACX requires a noise floor below -60 dB RMS, which is a genuinely quiet room by home-recording standards. That doesn't mean the room matters more than the microphone, but it does get a vote: a good mic in a badly treated room will still produce a bad sound, because the mic faithfully captures all the reflections and background noise along with your voice.
Setting up a quiet space
My own background in audio comes from music: I studied music production and sound engineering, and for vocal recording I used a Neumann TLM 102, a nice crisp condenser mic. I only had access to proper vocal booths at certain times of day, so the rest of the time I recorded in my bedroom. I drew the curtains, gathered every blanket, rug and furry rag in the house, draped them over the cupboards and ran them along the floor, covering as much hard surface as possible. Soft, furry material absorbs sound, and the furrier it is the more absorbent it gets. That setup produced a professional, clear sound that stood up next to studio recordings, which proves a simple home setup can get you there.
- Curtains, rugs and soft furniture on hard walls cut both noise and reflections.
- Avoid small closets and tiny rooms unless they've been professionally treated. A closet full of clothes is not a good vocal booth; small enclosed spaces create a lot of reflections bouncing off the walls right next to the mic.
- Pick one space and use it for the whole book. Keep the mic in the same position, and keep yourself in the same position when you speak. ACX checks that files match each other, not just that each one individually passes.
How the room makes you feel matters too
Room treatment is only half of it. The other half is how you feel inside the room. Are you comfortable? Is the temperature right? Slightly cool is better than warm, both because sound travels best through cooler air and because heat makes long sessions harder. A professionally treated room won't rescue a tense, uncomfortable performance. Create an environment that lets you perform at your best, because the best out of you is the whole point of the recording.
Keep mic distance and gain identical every session
One of the easiest ways to create inconsistencies between chapters is changing your mic distance or input gain between sessions. A slightly different distance from the mic or a nudged gain knob 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, so it's worth capturing either way, but the bigger practical benefit is what happens in processing: it gives Optivox a second or two to analyse the true sound of your room before it starts adjusting anything.
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, since a clipped take can't be fixed afterwards.
- One file per chapter, with the chapter title spoken at the start.
- Listen back to a section before moving on to the next session.
Optivox masters your audio to ACX's RMS requirements
Once the recording is clean, Optivox's Audiobook mode masters specifically around ACX's requirements, including its RMS window and peak limit, while keeping natural room tone rather than gating every pause into digital silence. Upload a chapter, download the master and run it through ACX's own checker before submitting the full book.
If you want the numbers themselves broken down, see our full guide to ACX loudness requirements.