Playing back digital audio has turned into a regular experience for most computer users thanks in part to a variety of formats that helped make audio smaller in size, allowing simple methods of digital distribution. There are many different formats that serve many different purposes. Need to know FLAC from MP3? We've broken down each format and its main purpose in this audio formats primer.

MP3
The most popular audio format, and the one that largely changed music as we know it, is called MP3. MP3 is a relatively old format and part of the first set of MPEG specifications governing the playback of both audio and video. MP3 actually stands for MPEG1 layer 3, and because of the name some people often confuse it with the audio/video standards MPEG-2 and MPEG-4.

MP3 is a lossy codec, which means when files are encoded to MP3, the encoder chooses which parts of the audio are most important, and discards other less important parts. This process results in audio files that are passable, but less complete than the original file. Depending on the bitrate at which the file is encoded, more information can be kept or thrown out. This "lossy" nature, like all MPEG codecs, makes it an ideal candidate as a delivery format, meaning a format for mass consumption, rather than an archival format. MP3 doesn't have any sort of digital rights management (DRM) built-in, meaning most MP3s can be transferred to any device and be expected to play.

AAC
MP3's ideal successor is AAC, which stands for Advanced Audio Codec. AAC was largely designed to be the next version of MP3, and accomplishes things like better quality audio at similar bitrates. That means AAC will sound better than similarly sized MP3s. While AAC might be the successor to MP3, thanks to MP3's 10+ year lifespan as a file format, MP3 is supported with most devices whereas AAC doesn't have the breadth of support in hardware devices by comparison. However, that's not to imply that AAC doesn't have a broad install base. Most notably, iPods can play AAC files back natively, and every track purchased in the iTunes Music Store is an AAC file.

Unlike MP3, AAC has seen some DRM implementations, again most notably in the iTunes Music Store. While not defined as part of the AAC specification, Apple has forked AAC to try to thwart music copying. The implementation, known as FairPlay, requires listeners to be using iTunes, and have a computer authorized to play the music before being able to actually listen to the files. Apple limits the computer count to five total activated iTunes accounts at a time (check out our guide to deauthorizing all those iTunes accounts at once if you ever hit your limit and find the need).

OGG
Another lossy audio format is the OGG format. OGG is a "free" format, meaning the format is maintained by the not-for-profit Xiph.org foundation, and doesn't charge for licensing or implementation. OGG is a file format popular with open source computer users, since there is no corporation sponsoring the format and all of the format's specifications and encoding methods are open and public. OGG is a less popular format, one not sanctioned by any store selling legal tracks, however many users transcode their music collections into OGG typically using the compression format called Vorbis. OGG files do not typically have any implementation of DRM, since the idea of DRM is counterintuitive to the nature of open source.

WMA
One format known most notably for its wide variety of DRM implementations is WMA, short for Windows Media Audio. WMA was created by Microsoft, likely as a response to the rise of other lossy codecs like MP3. WMA's main use is in subscription and pay-per-download music services. Microsoft created WMA to have wide copy protection measures in the files, seemingly to lure music industry labels to its side and make money off of licensing fees. Music services like Wal-Mart's online store, as well as Napster and Yahoo!'s music store all use WMA audio, with Napster utilizing a subscription model, and the other two utilizing a purchased downloads model.

The actual WMA codec consists of four sub codecs. The original WMA codec is the lossy codec that competes with MP3. WMA Pro is an audio codec that has extended support for multi-channel audio, and also works with higher resolution audio. WMA Voice targets voice-only content and works at much lower bitrates by constraining the encoder to vocal frequencies only. Lastly, WMA Lossless is a lossless codec, meaning the complete data from the original master is maintained; however, the audio is compressed to allow ease of transfer.

FLAC
Another lossless audio codec is the Free Lossless Audio Codec, commonly referred to as FLAC. FLAC is popular with the audio enthusiast scene, as the files created are smaller than WAV files, though the files still maintain all the audio fidelity of a WAV file. FLAC files can also be paired with "cue sheets" that define individual tracks inside of one larger FLAC file. FLAC files cannot be played back with most portable audio hardware, requiring either modified iPod firmware or custom portable players, but several notable players support it such as several in the Cowon line (including the Cowon A3, and iAUDIO 7) as well as the iriver SPINN, the SanDisk Sansa slotMusic player, and a number of Samsung PMPs including the YP-S2. FLAC's other primary advantage is that it is free, and any device manufacturer can implement FLAC at no charge. If you're looking for components to handle your FLAC collection, an updated list of many of the devices that support FLAC is kept at Sourceforge.

ALAC
One lossless format implemented on the most popular portable media player, the iPod, is the Apple Lossless Audio Codec (ALAC). ALAC allows users to take audio straight from CDs, convert it in iTunes to ALAC, and play it back in full fidelity on an iPod. ALAC files can only be played in Apple's music ecosystem (iTunes, Quicktime and iPod) and therefore the format is mainly suitable for audiophiles who enjoy listening to lossless music on an iPod exclusively.

WAV and AIFF
Most lossless audio comes from an originating source that has a bit-by-bit file that actually maps all the points on a sound wave. The two main formats of choice for complete recording are WAV (pronounced wave) and AIFF (sometimes pronounced "Aee-ph"). Both file formats are devoid of any sort of compression, making an average pop music song three or four minutes in length a hefty 50MB. While not as large of an issue in modern computing, 50MB file sizes in the mid to late 90s made the transfer of audio files extremely difficult, which is why lossy codecs were born. WAV is typically the Windows standard for audio storage, while AIFF is the Mac standard, though in modern usage both work interchangeably on either operating system. The WAV and AIFF formats are typically seen as "master" or "archive" formats, meaning they aren't typically distributed to the public since the file sizes are large, though the audio quality is much higher than any lossy codec.

Close cousin: MIDI
Lastly, one format that isn't specifically an audio format but should likely be mentioned is MIDI. Short for Musical Instrument Digital Interface, MIDI files don't actually contain any audio data, but rather contain references to timing and volume of notes, which can be interpreted by any MIDI capable device. Before MP3 took its throne as the format du jour of music pirates, MIDI files would be swapped around the internet in the same way that MP3s are traded. MIDI files are extremely small, often ranging in size from eight kilobytes up to a few dozen kilobytes on the "large" end.


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