ACX Audio Submission Requirements

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.

More information on how to meet these requirements can be found in our Video Lessons & Resources, and many of the terms used here can be found in our Audio Terminology Glossary.

Your submitted audiobook must:

Be consistent in overall sound and formatting.

    Why? - Consistency in audio levels, tone, noise level, spacing, and pronunciation helps give the listener a great experience. Drastic changes can be jarring and are not in keeping with a professional production. Extreme fluctuations in volume means the listener will have to keep a hand on the volume control of their listening device. This detracts from the listening experience and may lead to poor reviews and reduced sales.

Be comprised of all mono, or all stereo files.

    Submitted audiobooks may not contain both mono and stereo files. Stereo files must be “stereo interleaved”. Mono files are strongly recommended.

    Why? - Before being added to the Audible store, submitted audiobooks are encoded in a variety of formats that listeners have the option of downloading. Titles submitted with both stereo and mono files will cause errors during this encoding process and the title’s retail release may be delayed.

Include opening and closing credits.

    At minimum, the opening credits must note the name of the audiobook, the name of the author(s), and the name of the narrator(s). Closing credits must, at minimum, state “the end”.

    Why? - Opening credits help listeners confirm what they are about to hear, and that they are listening to the start of the audiobook! Closing credits confirm to the listener they have reached the end.

    Recommended Opening Credits:
    “[title of audiobook]"*
    Written by [name of author]*
    Narrated by [name of narrator]*

    Recommended Closing Credits:
    This has been [title of audiobook]*
    Written by [name of author]*
    Narrated by [name of narrator]*
    Copyright [year and name of copyright holder]
    Production copyright [year it was recorded] by [company name]

Sections marked with an * are required.

Include a retail audio sample that is between one and five minutes long.

    This sample should start with narration, not opening credits or music. If the audiobook is erotic, the sample should not include explicit material.

    Why? - The retail audio sample used on Audible and Amazon is a preview of your audiobook. A great sample will show off your material and attract paying customers! (Note: iTunes automatically uses the first five minutes of the book as their sample.)

Be narrated by a human. Text-to-speech recordings are not allowed.

    Why? - Listeners purchasing audiobooks from Audible and partner channels expect them to be narrated by people!

Each uploaded file must:

Contain only one chapter or section.

    You’ll be prompted to upload each file individually. Both the opening credits and closing credits must be separate files.

    Why? - This ensures listeners can easily navigate between sections, and that skipping forwards or backwards moves them forward or back one section. Combining multiple sections in one file creates a confusing navigation experience. If the audiobook is not in a traditional chapterized format and you’re unsure how best to separate your files, please contact audio@acx.com for guidance.

Measure between -23dB and -18dB RMS.

    Why? - Put simply, this means the files fall within a specific volume range. By keeping all files within this range, listener experience is enhanced – not too loud, and not too soft. In being consistent, listeners won’t have to constantly adjust the volume of their playback device.

Have peak values no higher than -3dB.

    Why? - By leaving this headroom you’ll reduce the possibility of distortion, which can seriously reduce the quality of the listening experience. This headroom is also needed to ensure files are successfully encoded.

Have a noise floor no higher than -60dB RMS.

    Why? - Noisy files make it difficult for listeners to focus on the material.

Be 192kbps or higher MP3, Constant Bit Rate (CBR)

    Why? - Before going on sale in the Audible store, titles are encoded in a variety of formats that customers have the option of downloading. 192kbps (or higher), Constant Bit Rate MP3 files are required so this encoding process works without error. You may upload 256kbps or 320kbps files if you’d like, but the difference in quality heard by listeners will be negligible.

Be 44.1 kHz

    Why? - Before going on sale in the Audible store, titles are encoded in a variety of formats that listeners have the option of downloading. 44.1 kHz files are required so this process works without error.

Be no longer than 120 minutes. Files longer than 120 minutes are not supported.

    If a section will be over 120 minutes long, find a good break in the narration, and split the section into two files. If the section began with a header, such as “Chapter 2”, we recommend starting the second file with “Chapter 2 continued”. This will help ensure listeners can easily navigate from section to section.

Be no larger than 170MB. Files larger than 170MB are not supported.

    If a file will be over 170MB, find a good break in the narration and split the section into two files. If the section/part began with a header, such as “Chapter 2”, we recommend starting the second file with “Chapter 2 continued”. This will help ensure listeners can easily navigate from section to section.

Contain the section header, if contained within the text (e.g., “Prologue”, “Chapter 1”, “Chapter 2”).

    Why? - By including these announcements, you’re helping the listener understand what section of the book they are listening to without having to look at their player. Be consistent - a listener may think content is missing if most headers are read, but some are not.

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.

    Why? - Leaving this space gives listeners an audio cue that they have reached the beginning or end of a section. This space is also required to ensure titles are successfully encoded in the many formats made available to customers.

Be free of extraneous sounds such as plosives, mic pops, mouse clicks, excessive mouth noise, and outtakes.

    Why? - Extraneous sounds can be distracting to listeners, and outtakes sound unprofessional. Each can elicit bad reviews and bad reviews can hurt sales!