ACX technical requirements — complete list
ACX (Audiobook Creation Exchange) has specific technical requirements for all audio submissions. Files that do not meet these specifications are rejected during quality review. This checklist covers every requirement as of 2026.
Format
MP3
Constant bit rate, 192kbps minimum. Variable bit rate not accepted.
Sample Rate
44.1 kHz
Standard CD quality. Most recording software defaults to this.
RMS Level
-23 to -18 dB
Most common rejection reason. Normalize in Audacity — free software.
Peak Level
Below -3 dB
No clipping. Audacity's normalize function handles this automatically.
Noise Floor
Below -60 dB
AI-generated audio passes this automatically — no room noise.
Room Tone
0.5-1 second
Silence at start and end of each file. Add in Audacity.
File structure requirements
- Retail sampleFirst 5 minutes of content — this is what potential buyers hear. Usually the opening of Chapter 1. Submit as a separate file.
- Opening creditsMust include: title, author name, narrator name. Keep under 30 seconds.
- Chapters as separate filesOne MP3 per chapter. Named sequentially: 01_chapter_one.mp3, 02_chapter_two.mp3, etc.
- Closing creditsTitle, author, narrator, copyright year. Required by ACX.
- No background musicACX does not allow background music under narration unless it is your own original composition with proof of rights.
How to normalize audio in Audacity (free)
- Download AudacityFree at audacityteam.org — available for Windows, Mac, and Linux.
- Open your MP3 fileFile → Open → select your exported AudioForge chapter file.
- Select all audioEdit → Select All (Ctrl+A / Cmd+A)
- Run Effect → Loudness NormalizationSet target to -23 LUFS (integrated). This hits the ACX RMS window.
- Add room toneGenerate → Silence → 0.5 seconds. Paste at the start and end of the track.
- Export as MP3File → Export → Export as MP3 → set to 192kbps constant bit rate.
AudioForge handles the audio generationAudioForge creates your MP3 files chapter by chapter using OpenAI TTS (professional quality) or browser TTS (free preview). The built-in ACX checklist shows you exactly what to verify. Audacity handles the final normalization in about 30 seconds per chapter.
ACX royalty rates — what you keep
| Distribution Option | Royalty Rate | Notes |
|---|---|---|
| ACX Exclusive (Audible/Amazon/iTunes) | 40% | 7-year exclusivity. Higher rate, limited reach. |
| ACX Non-Exclusive | 25% | Distribute elsewhere simultaneously. Findaway, etc. |
| Findaway Voices (Wide) | 80% | Distributes to 40+ platforms. No exclusivity required. |
Most authors start non-exclusive with ACX and add Findaway for wide distribution. You can always move to exclusive later if Audible is your strongest sales channel.