To have your audiobook approved, it must meet the following audio quality standards:
1. Audio files must be consistent in overall sound and formatting, including loudness ranging between -23dB and -18dB RMS and have -3dB peak values and a maximum -60dB noise floor.
This is best achieved by a creating a consistent recording and the use of compression, limiter, EQ and metering tools in post production. Read this article for more information about loudness and target levles.
2. The audiobook must include opening and closing credits, be comprised of all mono or all stereo files, as well as include a retail audio sample that is between one and five minutes long
3. Each audio file must contain up to one chapter/section per file, with the section header read aloud, have a runtime no longer than 120 minutes, as well as conatin room tone at the beginning and, free of extraneous sounds.
4. The required formats are: 192kbps or higher MP3, Constant Bit Rate (CBR) at 44.1 kHz
As long as you adhere to the requirements listed above, your audiobook will be successfully submitted to ACX. Good luck in audio production!