Squeeze box

Previously, efforts to deliver high-quality media online kept choking due to bandwidth limitations. MP3 and similar formats -- such as Windows Media Audio and Liquid Audio -- can shrink music files with minimal loss of audio quality. Hogging space on your hard drive at a rate of 10MB per minute, a standard uncompressed hour-long CD requires about 600MB of storage space. But MP3 and other formats can squeeze that same disc into just 60MB of disk space, without significantly degrading its quality. At this level of compression, the resulting sound is "near-CD quality". Users can encode tracks at any of several sampling rates and corresponding levels of audio fidelity, ranging from transistor radio to CD quality.

At the heart of compressed-audio formats lie codecs -- coders/decoders -- that compress and play back audio files. Each format has its own proprietary codec, usually incompatible with other formats. You can store and replay these small music files through a cheap (or free) player on your PC. Currently, only MP3 files can be played back on a portable device, like RioPort's Rio 500 and Creative Labs' Nomad, though we'll soon see other formats on these and other devices. Major players (such as Lucent Technologies and Microsoft) have developed their own codecs that compete with MP3.

Encoders shrink sound files by removing redundant data from them. "If you play the game right, you can throw away a surprising amount of data," says Amir Majidimehr, Microsoft's director of audio/video compression. Microsoft's Windows Media Audio encoder is a case in point: "At 64Kbps, we toss out 96 per cent and keep the four per cent we want," says Majidimehr. Yet to the human ear, the clip sounds nearly identical to the original.

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