Conference cookie::notes$archive:cd_v1

319.0. "Ramblings of one who deals with A/D conversion." by PYRITE::WEAVER (Dave - Laboratory Data Products) Wed Mar 26 1986 20:11

All older and most modern day recordings started off as an analog signal.
The advantage of converting the signal to digital early in the recording
process is to prevent analog signals from being distorted by other analog
components and probably most important the media that the signals are
stored on. The earlier you can convert the signal to digital, the less
likely the possibility of additional noise being injected (or induced) into
the system. 

What a lot of people don't realize is that digital signals have the
potential for creating a lot of analog noise, and without proper isolation
of digital components from analog, you can get more "crap" than you
would if you stayed with an analog mix.  Also the quality of the A/D
converters is going to play a factor, as well as the temperature of
the room where the A/D conversion is taking place.

By using a good analog system for recording, you can be assured of
producing a good tape for input into a digital system to convert to
CD.  By using a good digital tape system for initial recording you can
also be assured of a good CD.  But take a bad analog system, or a bad
digital system (one that may not have good isolation of the digital
from the analog) and you will get a bad CD.  I feel like I am stating
the obvious here, but some people seem to have some hangups.

Digital recordings will have a much longer shelf/playback life than
an equivalent analog recording because the signal to noise ratio of
a bit being on or off in a given media is much higher than that of an
analog signal in the same media.  Hence, you can mass-reproduce a digital
recording far more reliably than an analog recording.  This is what
makes digital recordings more advantageous than the analog counterpart.
Digital processes also allow for the recovery of "lost" data by ECC
correction.

Some of the older analog master tapes may suffer from some signal
degradation, while a comparable digital tape probably wouldn't suffer
signal degradation in the same timeframe.  Hence, some of the older
analog masters may have more hiss and dropouts than when they were first
transcribed.

The only time that a recording doesn't originate from an analog beginning
is in the case of a digital synthesizer, which is creating analog waveforms
digitally, and therefore more perfectly (not perfect, given the
quantization and errors produced by quantization).  The only errors
to worry about in this setup are those caused by the D/A circuitry for
playing back the synthesized signals and the analog circuitry that
amplifies the signal to a level that can be handled by the speakers.
Then of course, we have the distortion caused by the speakers and
room acoustics.

I believe that a lot of the "harshness" attributed to CD's is due to bad
digital recording techniques, and the ability of the digital media to
accurately reproduce the high frequencies, which tend to be more "rolled
off" when playing back on inferior analog equipment.  The complaints of
many "golden ears" about "harshness" is probably due to the fact that they
are playing CD's on media which can more accurately reproduce the high's,
and therefore make bad CD's more noticeable.  Also note that the early
players probably didn't isolate the digital signals from the analog well
enough for playback.  The cheaper CD players won't have as much
digital/analog isolation as the more expensive players (Nak's design looked
the best on paper about a year ago).  Therefore a cheaper player won't
sound as good on a better system.

"Digital noise" is analog in its nature and can be quite audible if
not dealt with correctly.  If you are planning to upgrade your system,
but want to buy a CD player first, be careful.  What you hear now may
be different later.  A stereo system is only as good as its weakest
link.

					Enough rambling...
					-Dave