[filmscanners] RE: keeping the 16bit scans

["Austin Franklin" <austin@darkroom.com>]

Hi Art,

> After CDs became entrenched, many were torn up over the limited sampling
> rate of CD recordings, claiming analogue would remain king, because it
> was so "warm" and full of "harmonics" and "full" of natural depth, etc.
> etc.  They told me of the problems with cut off filters, and inherent
> design flaws of digitally recorded music.

One of the inherent design flaw in the initial CD players was that they
either used none, or used 3rd order filters to filter the output.  The
problem with a 3rd order filter is it delays different frequencies different
amounts.  The problem with no filter, is the sound is "staircased", and does
not sound very good.

The solution was to "oversample" the output.  In other words, interpolate
the data between the samples. Typically, this is done now with an 8x
oversampler that takes N 44.1KHz samples in, and generates an 8X samples out
at 8x44.1KHz.  This removes the need for 3rd order filtering, and allows
first order filtering to be used, therefore alleviating the problems
associated with a 3rd order filter.  In other words, the sound is much
better ;-)

Another problem that early CD players had was jitter in the clock.
Basically the same as "wow and flutter" for a tape or record.  They just had
to use better XTALs, and be more careful of how the circuits were designed.

And last but not least, is the dreaded EMI problem in CD players.  With all
that high speed digital logic in there, it can, unless properly designed,
couple into the analog section.  With proper filtering and design, the
output can be exceptionally clean.  This can be an expensive proposition
though, and only the mid-range and high-end player really have addressed
these problems.  With the "proper" system, the better CD players are
noticeably better in this regard.  This issue also is what led to "separate"
D/A convert boxes, and separate transports.

Regards,

Austin



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