AviationBanter - View Single Post

Keith Williams

In article ,
lid says...
We previously went through this crap with CD players.
The sampling frequency was chosen to be 44.1 kHz, well
beyond the range of human hearing. No filtering would
be needed.

Your story is ready for Snopes (sounds good, but less than the
truth). To get to a 20kHz bandwidth the signal must be sampled at
greater than 40kHz (see Nyquist). If *everything* above the
nyquist limit isn't filtered these artifacts will be aliased.
Given that most engineer's junkbox doesn't contain perfect filters,
2kHz is left for the filter, thus a sampling rate of 44.1kHz.
T'was a trade-off of device complexity and data storage (running
time).

Except for one thing...when they played the CD back
unfiltered, people would find their tweeters melting
for some weird reason....44.1kHz! at huge powers!

BS. Were it unfiltered aliasing would make the CD sound terrible.
The filter has to be in there for any sampled system. They didn't
"all of a sudden" figure out that they needed a filter.

Out came the drawing board and complex analogue (and
expensive) filters were designed until one day some
smart engineer discovered they could double the freq.
in a computer and put out 88.2 kHz sampling noise and
use a less efficient and less expensive filter.

Less expensive filter because there is more headroom.

snip

--
Keith