MP3 (MPEG-1 Audio Layer 3) is easily the most recognized digital file format. Almost everyone associates MP3 with music, and this recognition factor is due in large part to the music industry's well-publicized legal battle against MP3 distribution. Even though there is a strong association between music and MP3, many people have no idea what MP3 actually is.

MP3 is a compression algorithm that reduces the size of audio files considerably. Audio data in the form of stereo CD recordings takes a tremendous amount of hard drive space, so before the development of audio compression, trading audio files was impractical. Thanks to MP3, audio files could be compressed to about 1/10 of their original size while still retaining good audio quality. This allowed people to upload and download songs on the Internet, bringing the full wrath of the established music industry on music distribution services like Napster.

Today, the music industry has embraced MP3 to some extent, and Internet web sites such as Apple's iTunes allow people to download songs for a fee.

What Does MP3 Do?

As we stated above, MP3 is a compression algorithm. Typical audio CDs are recorded at 44,100 Hz and 16 bits. This means that 44,100 audio samples are recorded each second and each sample is 16 bits. This is a constant data stream which is equivalent to about 10 MB per minute of stereo audio.

MP3 works by throwing away some of this data, particularly frequencies which are beyond human hearing. The trade-off is reduced sound quality, but for many people the difference is not noticeable. Sound quality can be improved by encoding the audio at higher bit rates, but this results in larger files.

The big advantage of MP3, of course, is the compact file size. Audio files which are encoded at 128 kb per second are approximately 1/11 the size of the original audio file. As well as permitting Internet distribution of songs, the small size of MP3 files has also spawned the MP3 player market. MP3 players are compact devices (sometimes no bigger than a cigarette lighter) that can hold hundreds of songs. MP3 players are currently one of the hottest consumer items in the world.

The process of applying an MP3 algorithm to an audio file is called encoding. For playback purposes the file must be decoded. For this reason, audio players need a codec (enCOder / DECoder) to play MP3 files. These codecs are included in virtually every portable audio player.

MP3 is not the only kid on the block, however. There are many other formats for compressing audio. Support for these alternative formats is not universal, so when shopping for a portable audio player, one of the big considerations is the type of files it can handle.

The second most popular format after MP3 is WMA (Windows Media Audio). This is a Microsoft format that claims to offer higher audio quality at lower bit rates. Lower bit rates translate into smaller file sizes, one of the reasons for the popularity of WMA.

Apple iPod portable music players support the AAC (Advance Audio Coding) format. AAC allows more than two audio channels (up to 48) and handles higher frequencies better than MP3. The result is better sound with smaller files.

Another format that is growing in popularity is Ogg Vorbis. This is an open-source codec that carries no licensing fees and has a sound quality equal to or better than MP3.

For those concerned with audio purity, many players also support uncompressed audio files (WAV). However, at 10 MB per minute, very few WAV files can be stored on the typical portable audio player.

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