Streaming Music, Podcasts, & Audio What Is the Audible Format? About this proprietary digital audio standard by Mark Harris Writer Mark Harris is a former writer for Lifewire who wrote about the digital music scene and streaming music services in an easy to understand, no-nonsense manner. our editorial process Mark Harris Updated on June 25, 2020 Music, Podcasts, & Audio Audio Streaming Spotify Pandora Apple Music Prime Music Music For Your Life Podcasts Radio CDs, MP3s, & Other Media Tweet Share Email Audible is a popular audiobook and spoken-word platform. When you purchase a book, podcast, or other spoken-word title from Audible, it's added to your account and delivered to you as an audio file. Here's a look at the proprietary Audible format and how to listen to your spoken-word downloads. When you buy a book from Audible, it's yours forever. If Audible retires a format, you'll be able to download your title again in a new, improved format. Downloading an Audible Title When you purchase a title on Audible and add it to your library, you have the option to Listen Now or Download. If you're on a computer and select Listen Now, your title will begin playing immediately via Audible's Cloud Player, which streams your title on a Windows PC or Mac. If you select Download, the file will download to your computer in Audible's proprietary .aax format. If you're using the Audible app for iOS, Android, Windows Phone, Alexa-enabled device, Fire TV, or another supported device, you can stream the title from your device or download it and add it to your Library, so you'll be able to listen to it whenever you want, even when you're not on Wi-Fi. About Audible's Proprietary File Format When you purchase a book on Audible, you used to have the option of downloading the file in Enhanced format (.aax) or Format 4 (.aa). However, as of June 2020, Audible has phased out Format 4 (.aa) and will only support Enhanced format (.aax). If you previously purchased a title in Format 4, you can download it again in the currently supported format. The Audible formats .aa and .aax covered a range of encoded bitrates. These sound formats were designed to give you a choice about the sound quality level you wanted when you downloaded your audiobooks. With Format 4 (.aa), sound was encoded at 32Kbps, and the quality of sound was categorized at standard MP3 level. With Enhanced (.aax), sound is encoded at 64Kbps and is deemed as having CD-quality sound. As devices have improved, Audible decided to stop supporting Format 4, aiming to provide all users with a higher-quality listening experience. Having the Format 4 choice made sense when more people had older devices didn't support Audible's Enhanced bitrates, but this is no longer the case. Earlier incarnations of Audible's proprietary format included Format 2, which had a bitrate of 8Kbps and sound on par with AM radio, and Format 3, with a bitrate of 16Kbps and sound on par with FM radio. Both of these formats had the .aa file extension. About Audible File Format Conversions Users can't convert Audible audio files from the .aax format to another format, such as MP3. Audible's proprietary .aax format has security technologies that protect the intellectual property rights of content providers, while offering an enhanced listening experience for users.