From: utzoo!decvax!duke!harpo!npoiv!alice!rabbit!jj
Newsgroups: net.audio
Title: Re: Digital vs. analog
Article-I.D.: rabbit.616
Posted: Sun Jul 18 21:59:49 1982
Received: Mon Jul 19 01:08:26 1982


	I must admit that I find it difficult to reply to the article by
Kim Rochat, although not because the arguements are difficult to refute.
They are, in fact, not that difficult to refute, to another signal processing
person.
	Disgegarding the opinion statements about Golden Ears, I will
begin my comments by addressing the statements about rise time in analog
equipment.  It is indeed limited, and quite severly, (in a record, for example)
after several passes through the playback device. (This statement holds for
magnetic recording, also, but a discussion of the causes is beyond this
note).  In addition, records, which do generate signals with a very
high rise time, most often do so (even in the case of the best records and
cartridges)  as a result of tracing distortion or mistracking.
	Even if the signal being reproduced does have an undistorted
risetime on the order of 10us, the transducer that reproduces it and
the travel through the ear will spread it out, due both to filtering
and dispersion.  There have been several, although few and far between, papers
that have discussed the variability of DISTORTION with respect to signal
risetime.  Most transducers, do, in fact, have measurable non-linearities
that arise during highly slewed parts of the signal.  These non-linearities
have been shown to be perceptable.


	Regarding the recording of digital at half speed:
There are indeed converters that are capable of converting at
100kHx.  The converter is not the problem.  STORAGE of the information is
the problem.  Your scheme of slowing down the digitization of the
signal will do the following:
1) Make no difference whatsoever in the Digital sense
2) Introduce a distortion of about 2%  due to the
nonlinearities in the magnetic recording process.
3) Limit the dynamic range to 60-65dB  OR introduce low frequency distortion
as a result of compression/expansion.
4) Introduce the most annoying (to me) problem with magnetic recording tape:
Head Scrape/Flutter.  This bizzare process is the result of sliding a tape,
with a finite coeffecient of friction, against the tape head.  It has nothing
to do with the flutter due the drive system, etc.  This is the process that
causes the "closed in' sound that is often attributed to magnetic recording.
5) Double the storage required for the signal.
	To summarize.  Your method of making digital recordings would
eleminate the beneficial aspects of digital recording, without making
any change in the problems involved.