ACX audio spec checker

Check an audiobook file against the ACX submission spec, free and directly in your browser. Drop in a chapter and see RMS level, peak and noise floor measured against the real thresholds, with a pass or fail on each one and a plain reading of what to fix. Nothing is uploaded, so it is safe to run on unreleased work.

In your browser
Drop a chapter file here, or choose one
WAV, MP3, M4A or OGG. Measured on your device, never uploaded.
Choose file
Runs in your browser. Nothing is uploaded. This is a free tool from Vocast.

How it works

1
Add your file

Drop or choose a chapter file. It stays on your device.

2
Measure

Your browser measures RMS level, peak and noise floor.

3
Check

Each metric is checked against the ACX threshold and marked pass or fail.

4
Fix and recheck

Read the one line guide on anything that failed, fix it, then check again.

Frequently asked

Three measurable ones: RMS level between -23 dB and -18 dB, peak at or below -3 dB, and a noise floor at or below -60 dB RMS. Human review items such as pronunciation are out of scope.

No. The file is decoded and measured in your browser and never leaves your device.

It means the file meets the measurable technical spec. ACX also reviews performance and consistency, which no tool can check for you.

Reduce the room noise at the source if you can, then run the file through the free noise remover and check again.

Related tools

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Noise remover
Strip hiss, hum and room tone while your words stay clean. A/B the result and download.

Audiobook narration in your own voice

This is the free checker. To narrate whole chapters in a voice cloned from your own, fully local and one time, get Vocast for $49.

Get Vocast for $49See features