ACX is the Audible/Amazon marketplace for Audiobooks. Once you have recorded, mastered and encoded your audiobook, its time to submit to ACX. They have very specific requirements for the audio. They analyze this data (using automated software, they don’t actually listen to it) to make sure that the audio is up to a professional standard.
There is a great plugin for Audacity called ACX Check by Will McCown. It will analyze your audio file and tell you if you have passed/failed on the ACX Submission Requirements.
It checks the following:
- Peak Levels: The greatest absolute value in the audio selection.
- RMS Levels: The RMS level of the audio selection
- Noisefloor: The RMS level of the quietest 500ms in the audio selection.
- Noisefloor (A): The noise floor of the audio selection with an A-Weighting filter applied
- DC Offset: The DC (overall average) of the audio selection
This plugin was created with great intentions, but please be aware that it is not the exact set of tests that ACX will perform on your audio files. For example, the Noisefloor check looks at the quietest 500ms in the audio selection. I believe that ACX uses a much more intelligent algorithm to detect the noise floor. Not just the quietest 500ms.
Its very easy to use. Just load up your MP3 into audacity, select the entire clip and click “Analyze” -> “ACX Check”.
It takes a little while to run based on the length of the clip, but once it has finished it will show a window with an easy to understand Pass/Fail dialog. If you have passed, congrats! It’s time to upload to ACX!