Free toolWill ACX accept your audiobook file?
Drop a chapter to check its RMS, peaks, noise floor and room tone against ACX's audio requirements, before you upload it. Measured in your browser, nothing uploaded.
Drop a chapter and see, line by line, whether it meets ACX's RMS, peak and noise-floor limits, and whether it has the room tone ACX asks for at each end. It doesn't check the export settings themselves: ACX wants MP3 at 192 kbps or more, constant bit rate, 44.1 kHz.
01Requirements
What ACX asks of every file.
- RMS level
- Between −23 dB and −18 dB
- Peaks
- No higher than −3 dB
- Noise floor
- No higher than −60 dB RMS
- Room tone
- 1 to 5 seconds at the start and the end of each file
- Format
- MP3 at 192 kbps or higher, constant bit rate, 44.1 kHz
- Files
- One chapter or section per file, 120 minutes at most, all mono or all stereo
Rules about who may narrate change too, so read what ACX, KDP and the other stores accept from AI narration before you start.
02Questions
About the ACX check.
Its overall level (RMS between −23 and −18 dB), its peaks (no higher than −3 dB), its noise floor (no higher than −60 dB), the room tone at each end, and the file format. A file that misses any of them comes back for changes.
It measures the same three levels the usual ACX checks measure, from the same definitions. ACX's people also listen to the audio, so a file that passes here can still be sent back for things a meter can't hear, such as mouth noise or mistakes.
Usually background noise: a fan, traffic, a hum from the computer. Record in a quieter room, or clean the recording before you master it. Don't fix it by gating to digital silence: ACX wants real room tone between sections.
Gently compress or normalise to bring the level up, then put a limiter at about −3.5 dB at the end of the chain, so the loud moments stay under −3 dB.
No. The file is decoded and measured by your browser. Nothing is sent to a server.
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