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Mirinex

Audiobook narration · Updated 20 October 2026

Your narration.
Ready for the ACX check.

ACX checks every audiobook file for its noise floor, loudness and peaks before it goes on sale on Audible. Two tools get a chapter close: one takes the room noise out, the other sets the loudness and keeps the peaks down.

ACX publishes its own audio submission requirements. Read them before you submit; this guide covers the audio levels only.

The three numbers ACX checks

Noise floor no higher than −60 dB: the hiss and room sound between sentences.

RMS between −23 and −18 dB: how loud the narration is on average.

Peaks no higher than −3 dB: the loudest single moments, such as a plosive or a raised voice.

Clean, then set the level

  1. Take the noise out first. Open the noise remover and choose the chapter. Listen to the quiet gaps between sentences: that is where the noise floor is measured. Download the cleaned WAV.
  2. Set the loudness and the peak ceiling. Open the audio normalizer with the cleaned file. Set the target loudness to −20 LUFS and the peak ceiling to −3.5 dBTP, then download.
  3. Check the result. The normalizer shows the loudness and true peak it reached. If it says the result is below your target to protect the peaks, your loudest moments are much louder than the rest. Lower them in your editor, or accept a slightly quieter file if it still measures above −23 dB RMS.
  4. Export as ACX asks. ACX wants MP3 files at 192 kbps or higher and 44.1 kHz. Export the final WAV that way from your editor.

Keep the room tone ACX asks for

ACX asks for a short stretch of room tone at the start and end of each file. Don't cut it to silence: digital silence can sound wrong. The cleaned room tone after noise removal is exactly what you want there.

Long chapters

Chapters of any length up to three hours can be cleaned. Anything over 20 minutes is done in parts of up to 20 minutes, each counting as one file of your plan, and joined back into one WAV.

Try it on a chapter

Hear the first minute of your chapter cleaned. Any plan cleans the whole chapter.

Clean up a chapter

Hear the first minute of your own file. Any plan processes the whole thing.

Related recording help

For loudness in more detail, see normalizing audio volume. For a podcast, see podcast and Zoom cleanup.