[Arny Krueger]

"Serge Auckland" wrote in
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A valid point. But how much of that harmonic distortion
is audible?

Harmonic distortion is not audible nor is it the intent that it be audible.
Harmonic distortion is an abstract means that is commonly, but often
erroneously used to characterize something that *IS* relevant, which is
nonlinear distortion.

The general rule is that nonlinear distortion that would produce 0.1% THD
if you properly chose to characterize it that way, can cause reliably
audible consequence.

It's hard to say as it depends on many factors. However,
tests done on harmonic distortion that I recall reading
many years ago indicated that 1% was the lower limit for
audibility, but it depended on frequency and masking by
other sounds.

The 1% rule is easy to debunk on the grounds that it can easily be too high.

As I recall, that was the origin of the
0.1% distortion desiderata for amplifiers as it was 10x
better than was likely to be audible, and could therefore
be comfortably taken as being completely inaudible under
all circumstances.

Actually, if I get to pick the music, there is a high probability that
nonlinear distortion of 0.1% in the 20-20 KHz range would likely be
objectionable to you, even if you were listening to a good car radio at 70
mph.

As to vinyl, I suppose one could cut a record from an
unequalised digital master and similarly produce a CD and
compare the two.

Vinyl is so limited in terms of dynamic range that many if not most digital
masters would require further processing if a good-sounding LP were the
desired outcome. It is perfectly trivial to create a digital master that
would damage most LP cutting equipment if not operated by an expert. The
expert would start out by changing the master. Producing an acceptable LP
from an unaltered digital master of ordinary music might be impossible.

However, the limited dynamic range that
would result from having necessarily to cut from an
unequalised master would not be a valid comparison with
"real world" LPs.

Agreed.

Practical LPs are cut from masters
specially equalised and compressed to get the best
subjective result from the limited medium. There is also
a great deal of skill (art rather than science) on the
part of the Cutting Engineer who will try and balance the
conflicting requirements of noise against level,
frequency response against level against distortion,
level against playing time and pre-echo, level against
playability by less sophisticated record players,
managing stereo difference i.e stylus vertical movement,
and possibly other things I haven't thought of.

Agreed.

If we want to compare the LP format to the CD format, we first have to bias
the test to favor the LP.

Obviously, unbiased comparisons of the two are impossible.