The Insider with Robert Harley -- Where's the Extra Data?

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The Insider with Robert Harley -- Where's the Extra Data?

Audio Trivia

The data rate of 44.1kHz/16-bit PCM audio as used in the CD format is 1.41 million bits per second (44,100 samples per second multiplied by 16 bits per sample, multiplied by 2 channels). If you've recorded uncompressed PCM (WAV files) on a computer, you know this is about 10.5MB per stereo minute.

But the raw data rate coming off a CD player's optical pickup is 4.3218 million bits per second, about three times the audio data rate. What's all this extra data?

Most of the extra bits are the result of eight-to-fourteen modulation (EFM), an encoding system that converts eight data bits to 14 bits during CD mastering. An additional two "merging" bits are added to each 14-bit chunk, resulting in a doubling of the data stored on the CD. Although EFM encoding doubles the data rate, it's actually a more efficient coding system than representing the data directly.

The other data are error correction codes, subcode (the data that identifies track length, start and stop points, and other housekeeping), and synchronization patterns to make the data self-clocking.

Notable Audio Quotation "Specialty markets in any high-end industry, including audio, are fundamentally about the experience they provide, not the stuff they make."

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