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Definition: MP3

(MPEG-1 Audio Layer III) The audio compression technology that revolutionized digital music (see "MP3 Shook Up the Industry" below). Derived from the audio sections of the MPEG-1 and MPEG-2 video specifications, MP3 compresses CD-quality sound by a factor of roughly 10, while retaining most of the original fidelity. For example, a 40MB CD track is turned into approximately a 4MB MP3 file. See CD-DA.

MP3 files are played on the computer via media player software, such as iTunes and Windows Media Player, as well as in iPods and audio equipment (see digital music player). MP3 sound quality cannot fully match the original CD, and true audiophiles complain bitterly, but millions of people consider it "good enough" because they can pack thousands of songs into a tiny pocket-sized device.

Converting a digital audio track from a music CD to the MP3 format (or other audio format) is called "ripping" or "importing," and this conversion function is built into iTunes, Windows Media Player and other jukebox software.

Bit Rates Are Important
While 128 Kbps is considered the norm for MP3 files, MP3s can be ripped to bit rates up to 320 Kbps. The higher the rate, the better the sound and larger the file. There are variations of MP3 and other widely used audio formats (see codec examples). See high-resolution audio, MP3 VBR and mp3PRO.

The Encoding Bit Rate
This dialog box from Windows Media Player shows "Audio quality" set to 192 Kbps. The slider selects four encoding rates: 128, 192, 256 and 320.

MP3 Shook Up the Industry
By the end of the 1990s, music fans discovered that a CD song title converted to MP3 would still sound pretty good even though it was only 1/10th the size of the original CD track. Smaller files meant faster downloading. At an average of 4MB, it took less than 15 minutes to download a file over an analog dial-up modem. With a broadband connection on a college campus, it took seconds.

MP3 created a worldwide auditioning system for new musicians who could freely distribute their music to gain an audience. It also let people swap copyrighted titles with impunity. File sharing services such as the original Napster and Kazaa made it a global phenomenon, and the record industry went into a frenzy over violations of its copyrights (see Napster). Today, copyrighted MP3 files are still shared over the Internet; however, online music stores, including the resurrected Napster, sell songs legally and successfully. See peer-to-peer network and DRM.

Developed in Germany
MP3 was developed in the late 1980s by the Fraunhofer Institute in Germany. Released in 1993, MP3 uses perceptual audio coding to compress the data by eliminating frequencies that would not normally be heard because they overlap and cancel each other. See ID3 tag, audioblog, podcast, iPod, AAC, codec examples, perceptual audio coding and cuckoo egg.

Proof of the Pudding
These examples taken in a Mac show the original CD file sizes (top) and the resulting MP3 files (bottom). The CD was ripped to MP3 in iTunes at a recording rate of 160 Kbps, and the album was reduced from 344MB to 39MB. When a music CD is inserted into a Mac, the CD's files appear in Apple's AIFF format, which is the same uncompressed 16-bit PCM format as the CD (see AIFF, CD-DA and PCM).