Audiobooks uploaded to ACX must adhere to the following requirements. The ACX Quality Assurance team may reject titles that do not meet these standards, and their retail release may be delayed. These requirements help ensure customers get a great listen.
Be consistent in overall sound and formatting.
Be comprised of all mono, or all stereo files.
Include opening and closing credits.
Sections marked with an * are required.
Include a retail audio sample that is between one and five minutes long.
Be narrated by a human. Text-to-speech recordings are not allowed.
Contain only one chapter or section.
Measure between -23dB and -18dB RMS.
Have peak values no higher than -3dB.
Have a noise floor no higher than -60dB RMS.
Be 192kbps or higher MP3, Constant Bit Rate (CBR)
Be 44.1 kHz
Be no longer than 120 minutes. Files longer than 120 minutes are not supported.
Be no larger than 170MB. Files larger than 170MB are not supported.
Contain the section header, if contained within the text (e.g., “Prologue”, “Chapter 1”, “Chapter 2”).
Have between 0.5 and 1 second of room tone at the head, and between 1 and 5 seconds of room tone at the tail.
Be free of extraneous sounds such as plosives, mic pops, mouse clicks, excessive mouth noise, and outtakes.