What Format Are iPod Files Stored In?by Andrew McClain
While the Apple iPod was originally a dedicated MP3 player, file formats supported by the iPod have increased over the years. Current iPod models play several different audio formats. iPods play both compressed and uncompressed audio files. Compressed audio is either "lossy" or "lossless." "Lossy" files lose bits of data during compression. "Lossless" do not lose sound quality, but you cannot compress them as much, so they'll take up more storage space. iPod-compatible files include ACC, MP3, Audible, Apple Lossless, AIFF and WAV files.
AAC files are Advanced Audio Coding files. They have the .aac file extension. Like MP3 files, AAC files use lossy compression. In fact, they were designed as the replacement to the MP3 format. As such, an AAC file offers better sound quality than an MP3 file compressed to the same size. Apple sells AAC files from the iTunes music store. Many other devices use AAC files, including the Playstation 3, Walkman and other music-playing phones.
The MP3 format offers a good trade-off between sound quality and file size, which makes them ideal for use in portable devices. The development of the MP3 format led to the rise of iPods and other portable audio players. Even though many devices use newer formats like AAC or Apple Lossless, MP3 files are still very easy to find.
Audible (.aa) files are the proprietary audio files distributed by audible.com. Typically, they are used for audiobooks or radio programs. Like MP3, Audible is a lossy format, so the quality of these files varies. The more compressed the file, the worse the recording sounds.
Apple developed the Apple Lossless compression. You can identify Apple Lossless files by the .m4a extension. As its name implies, this is a lossless format. It doesn't lose data during the compression process. You can compress a song from a CD down to half its size with this format. This also limits how much you can compress the audio file.
You can identify Audio Interchange File Format (AIFF) files by the .aif extension. The Apple OS frequently uses these files for audio, so much that they are also known as "Apple Interchange File Format." These files are uncompressed, so while professionals use them for recordings, they are not the best choice for storing audio files on your iPod. You should convert AIFF files to AAC or MP3 before you put them on your iPod.
Microsoft developed the WAV format. You can identify them by the .wav extension. WAV files are uncompressed, so offer high-quality recordings. Music files on CDs are typically WAV files. Due to their large size, they are also not the best choice to use on your iPod. Fortunately, there are several applications (including iTunes) that will convert WAV files to MP3 or AAC.
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