From: "George M. Anderson" <george@xxxxxxxxxxxxxxxxxx>
Analogy of course is audio CD players. When they first arrived if I
recall they were '2X' which meant either they sampled at the Nyquist
limit or double it, not positive which. They didn't sound all that good.
Within a year or 2, they were 8X or 16X, ie 4 and 8 times more sampling.
They sound good.
That's quite a bit different. In this case, "sampling" is a misnomer.
The CD analogy George uses is a output example, not a sampling
example. The data on the CD are fixed at 44,000 per second.
The early players were producing one analog point per digital point,
then using a steep, multi-pole filter to avoid the aliasing artifacts
Tim was describing. These "brick wall" filters typically have phase
distortion within the pass-band, which can make the sound harsh or
unnatural.
The multi-sampling players are taking two adjacent digital points,
and interpolating numerous in-between analog points. This allows them
to get away with a lower-order filter, which has fewer side-effects
(and is cheaper). Instead of a brick-wall filter with its phase
distortion, they can use a phase-linear Butterworth filter, which has
essentially no audible distortion.
: Jan Steinman <mailto:Jan@xxxxxxxxxxxxxx>
: Bytesmiths <http://www.bytesmiths.com>
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