Subject: Rudy Van Gelder: Digital vs Analog 
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Date: Sat, 22 Aug 1992 07:25:55 +0000

> No digital machine ever made could do that correctly either.  None.  Not even
> the best.  Well, I guess it depends on how you define "correctly."  I guess
> I don't know how Van Gelder defines it here, because I feel analogue
> recordings are more correct.
>
You are quite right although what you say is vapour comment, without 
reference. I respect your wish to prefer analog something but not that 
digitisation is flawed.

What I find amusing is the constant stream of reasons from some in  the  audio 
community as to why digitising and undigitising produces 'bad' sound.

In the early days there were deficiencies which were easily measurable but 
were not considered important, possibly leading to over-hyping of the 
technology. It certainly should be remembered that the analog equipment used 
for recording and playing back was (and still is) not so clever. Remember that 
this same analog equipment has to be used in front of and behind digitisation.

The _only_ thing to be discussed is whether the digitisation produces audible 
artifacts. I think we all accept that transmission of digital codes can be 
done perfectly, after all you are reading this message!

The present state of the art has all possible non linearities well below the 
listeners threshold of hearing given sensible listening conditions.

Noise is also below that threshold.

Low end frequency response has a practical lower limit set by analog 
considerations and things like the CD specification (no DC.). No conventional 
tape machine can compete, period.

Top  end  frequency  response  is in excess of 21kHz for CD or 22kHz+ for home 
recorded DAT. This may be a weakness. Analog can do  better  (1)  but  at  the 
expense  of  low frequency response. Digital could go much higher if it proves 
necessary.
  (1) analog has massive dynamic range problems if a wide frequency response 
      is implemented, digital has no problem whatever.

Group delay is now very close to perfection to 20kHz+, something where analog 
is a joke.

The transient response is limited by the Gibbs phenomenon. I have seen cheap 
CD players which show just this limit which is an incredible achievement.

For two channel or more, channel separation is near perfect.

Where does this leave us?

I guess that if things are being heard it is _nothing_ to do with the 
digitisation process as such.

I could produce a long list of known defects which can occur in both analog 
and digital systems, none of these have anything to do with inherent defects 
in the digital system.

About the only thing left (remember I am excluding ordinary and simply fixable 
problems) that I can think of is some unexpected  ability  of  humans  to  use 
supersonic  sound. The old idea of audio equipment sounding better if the high 
end frequency response rolled off gently might be used to counter this but the 
major reason for using the slow rolloff was because of group  delay  problems, 
something  that  cannot  be practically solved in analog but is dead easy with 
digital as has occured over the last few years. 

An analog tape machine? To avoid audible non linearities it would seem prudent 
to peak at -20dB ref 1% 3rd harmonic (usually the ref level).
The noise floor is 40dB below that if you are lucky.
If I had a dollar for every case I have come across of a tape machine being 
used as a compressor I would be well off.
Recording at typical levels adds harmonics and rolls off the top so it _will_ 
sound different.

How many suites using analog recorders use a peak meter to monitor level? This 
has led to some good laughs when digital recorders are installed -- where were 
all those 20 dB over the top peaks going? I'm serious!

Some people are now saying that PASC often sounds better, particularly if 
other than superb reproduction equipment is being used. No doubt you can guess 
as to why this is. Herein may lie the real reason why some people prefer 
analog recording but it not ok to shoot the messenger ie. digital.

Let's see if I get flamed!

  TC. 
    E-mail: tchannon@black.demon.co.uk or tchannon@cix.compulink.co.uk