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10.36 Why is CD digital data written in 44.1 kHz samples?




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This article is from the rec.audio.* FAQ, by with numerous contributions by Bob Neidorff others.

10.36 Why is CD digital data written in 44.1 kHz samples?

The rate of 44.1 kHz was picked to be compatible with existing
50 Hz and 60 Hz video-based digital audio storage, where an
integral number of frame buffers could fit in a single
horizontal scan. Quote from Watkinson and Rumsey, "Digital
Interface Handbook" 2.7.6 Choice of Sampling Rate:

"In 60 Hz [525 line, 60 Hz vertical refresh) video there are 35
blanked lines, leaving 490 lines per frame, or 245 lines per
field for samples. If three samples were stored per line, the
sampling rate becomes 60*245*3=44.1 kHz. In 50 Hz video [625
line, 50 Hz vertical refresh), there are 37 lines of blanking,
leaving 588 active lines per frame, or 294 per field, so the
sampling rate becomes 50*294*3=44.1 kHz. The sampling rate of
44.1 kHz came to be that of the Compact Disk. Even though CD
has no video circuitry, the equipment used to make CD masters
is video based and determined the sampling rate."

The length of 74 minutes is determined by the physical nature
of the reading system. It's based on the encoding method, the
wavelength of the laser used (different wavelengths are
incompatible with current CDs) and the necessary support
information. During the development of the CD, von Karajan was
alledgedly asked how long a CD must be, to which he responded
it must be long enough to hold HIS performance of Beethoven's
9th symphony, but the parameters had pretty much already been
nailed down at that point.

 

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