How to Fix ACX Rejections: Solving Noise Floor and RMS Errors
Rejected by ACX? Learn how to debug audio files, calculate RMS volume levels, and lower noise floors to pass Audible quality checks.
Eleanor Vance
Head of Digital Production
"Getting an audiobook rejected by the ACX quality assurance team can delay your release timeline. Rejections are typically triggered by technical audio engineering parameters: noise floor clipping, uneven volume levels, or incorrect track headers."
Core Key Takeaways
- Diagnosing and Fixing Noise Floor Failures
- Correcting RMS Volume Density Mismatches
- Meticulous Track Spacing and Formatting
1. Diagnosing and Fixing Noise Floor Failures
ACX requires a noise floor below -60dB. If your room is not soundproof, ambient hums (like computer fans or air conditioning) will fail checks. Use noise gates and high-pass filters to clean quiet sections.
- Record in an acoustically treated room to cut flutter echo.
- Apply a high-pass filter at 80Hz to eliminate sub-bass rumble.
- Use our free ACX Audiobook Spec Validator on the GIP tools menu.
2. Correcting RMS Volume Density Mismatches
Your tracks must stay between -18dB and -23dB RMS. Apply compression and limiting plug-ins to smooth out sudden loud peaks without distorting dialogue.
3. Meticulous Track Spacing and Formatting
Each file must contain exactly 0.5 to 1 second of room tone at the start, and 1 to 5 seconds of room tone at the end. Files must be constant bitrate 192kbps MP3s.
The Takeaway
Audiobook mastering requires professional sound engineering. Partner with the audio specialists at Golden Ivory Publishing to master and validate your chapters.
Bring Your Manuscript to Life with Golden Ivory
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