We get so many questions about MP3 that we felt compelled to explain briefly what MP3 is and how to use it. Here seems as good a place as any. MP3 is shorthand for MPEG-1 Layer 3 audio compression. MP3 has quickly become the most popular format for storing audio on computers. Although the music industry, concerned about piracy, has done its best to kill MP3 by filing lawsuits and introducing competing secure digital music formats, MP3 thrives and is likely to continue doing so.

The raison d'être for MP3 is that it compresses audio data significantly while maintaining acceptable audio quality. CD-Audio is recorded in stereo at 44.1 kHz with 16-bit sampling, and stored uncompressed as a 150 KB/s bit stream. Storing one minute of CD-Audio therefore requires 9,000 KB. A standard CD stores up to 74 minutes of audio, which translates to about 650 MB. Current hard disks are huge and cheap, but, at about 1.6 hours/GB, storing even a small CD collection on hard disk in CD-Audio format is impractical.

Enter MP3. MP3 uses lossy variable compression, which means that it stores important data—such as foreground sounds in the middle ranges to which the human ear is most sensitive—using moderate compression, but uses high compression for less important data, such as very high and very low tones and quiet background tones that are overlaid by louder foreground tones. Some data is discarded entirely, such as audio that is identical on both stereo channels and audio that is below the human hearing ...

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