To prepare an audiobook for ACX, split the narration so each chapter is its own file, with 1 to 5 seconds of room tone at the start and end. In AudioMultiCut you mark every chapter on one waveform and export all the chapter files at once, instead of exporting them one by one.
ACX also wants opening and closing credits as separate files, every file under 120 minutes, and a retail sample of 5 minutes or less. AudioMultiCut handles the splitting step. Loudness, noise floor and the final MP3 encoding are mastering steps, so do those in your editor or mastering tool after you split.
ACX file rules that affect how you split
| Rule | ACX requirement | What it means when splitting |
|---|---|---|
| One section per file | Each file contains only one chapter or section | Mark one segment per chapter, plus separate segments for opening and closing credits. |
| Room tone | 1 to 5 seconds at the beginning and end of each file | Leave a short pause before the first word and after the last word of every chapter. |
| File length | No file longer than 120 minutes | Split very long chapters into parts if they run past two hours. |
| Retail sample | 5 minutes or less, usually the opening | Cut a separate clip from the first minutes of the book. |
| Format | 192 kbps or higher CBR, 44.1 kHz MP3 | Export WAV from AudioMultiCut, then encode the final MP3 in your mastering tool. |
| Levels | -23 to -18 dB RMS, peaks below -3 dB, noise floor below -60 dB RMS | Not a splitting job. Master the chapter files after you split them. |
Requirements from the ACX help center, checked October 1, 2026. Check the current page before you submit.
Steps: split a narration session into chapters
The whole workflow runs in the browser. The audio is decoded locally and is not uploaded to AudioMultiCut servers.
- Open audiomulticut.com and load the session recording (WAV gives you the most room for mastering later).
- Find the chapter breaks. If you leave a long pause between chapters while recording, run Auto-Cut with the Lecture Chapters preset for a first pass, then adjust the edges by ear.
- For each chapter, move the start so there is 1 to 5 seconds of room tone before the first word, and the end so there is room tone after the last word.
- Mark the opening credits and closing credits as their own segments.
- Name the segments in order, for example 00_opening_credits, 01_chapter_one, 02_chapter_two, so the files sort correctly.
- Export as WAV and download all files at once.
- Master each chapter (levels, noise floor) and encode to 192 kbps CBR MP3 at 44.1 kHz in your editor or mastering tool.
Why export WAV, not MP3
AudioMultiCut's MP3 export is meant for everyday sharing, not for ACX's 192 kbps CBR rule. If you master after splitting, export WAV so you are not encoding to MP3 twice. Encode the final MP3 once, at the end, with the settings ACX asks for.
Other ways to do it
Audacity can do the same job: add a label at each chapter (Analyze > Label Sounds can find long pauses), then use Export Audio with the multiple files option. It is free and works offline, but takes more setup per book.
If you narrate in a DAW such as Reaper, you can mark regions and render each region to its own file. That is a good fit if you already master there.
AudioMultiCut is the quicker option when you have one long take and just need clean chapter files with room tone at the edges.
FAQ
Does ACX want one file per chapter?
Yes. The ACX help center says each file must contain only one chapter or section, with opening and closing credits as separate files.
How much silence should be at the start and end of each chapter?
ACX asks for 1 to 5 seconds of room tone at the beginning and end of each file, and no more than 5 seconds.
Can AudioMultiCut master my audiobook to ACX levels?
No. AudioMultiCut splits the recording and has a simple volume normalizer, but ACX's RMS, peak and noise floor targets need a mastering step in a dedicated tool.
Is my narration uploaded when I split it?
No. The website cuts the audio locally in your browser. The file is not uploaded to AudioMultiCut servers.
Sources
ACX help center checked on October 1, 2026.
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Related pages and tools
Split your narration into chapters
Load the session recording, mark each chapter, leave room tone at the edges and export every chapter file at once.