[net.audio] Digital Trojan Horse?

dsj@alice.UUCP (David S. Johnson) (08/22/85)

Has anyone else on the net heard of/thought about the claim
that digitally recorded (vinyl) LPs are destroying our turntables?

This hypothesis is argued in Neil Levenson's audiophile column
in the May/June 1985 issue of FANFARE (Levenson is a golden ear
who would do THE ABSOLUTE SOUND proud).  He claims that digitally
recorded vinyl discs generate ultrasonic products not present
in analogue discs (he claims these have been measured), which
somehow cause micro-cracks in turntable bearings (he claims
these have been seen under electron microscopes) which by some
mechanism greatly increase the short-term speed irregularities
of the turntable, especially audible on piano music.

Buttressing this argument are claimed measurements of
these speed irregularities, on a variety of new turntables.
Measurements were supposedly made both before and after digital
records had been played, with analogue records used as controls
so that the effect could not be due just to playing ANY record.
2-4 hours of digital play is supposedly enough to have a noticeable
effect and 12-15 is disasterous.  The effect does not go away
and applies to all subsequently played records, both digital
and analogue.

The implication is that the digitally-recorded LP is something
of a Trojan Horse: take them into your house and they will destroy
your turntable, thus making it necessary for you to buy a CD player,
since if nothing else CD players are rock-solid with respect to
speed accuracy.  (According to Levenson there IS nothing else;
he is of course firmly in the anti-digital crowd.)

Do these claims about speed accuracy damage seem at all plausible
to the experts on the net?

David S. Johnson, AT&T Bell Laboratories

jj@alice.UUCP (08/22/85)

I think it's a Trojan Horse.

The decent analog records I've seen, and ESPECIALLY the direct to disc
records, have significant energy to 50kHz or above, although only
in transients.  <i.e. there's nothing about 15-20kHz most of the time>

The digital recordings just simply do NOT have anything above 25kHz,
period.  I suspect that the highest sampling frequencies (64kHz), and
the resulting anti-aliasing filters ??25kHz??? establish the 25kHz
limit.

In any case, the argument is seriously suspect because digital recordings are,
by necessity, band-limited, whereas analog recordings are limited only by
the bandwidth of the recording chain, which can be considerably greater.


I have seen some results where pre-amps had absolute fits dealing with
transients with high ultrasonic content (in fact, I used to own one,
I did some work to find out just WHY some of the Crystal Clear records
I owned sounded so crocked on it...).  Needless to say, digital records
don't cause this problem.

The statement is, I believe, on a par with an article I saw a few years
ago in which an author claimed that even PLAYING ONE digital record on
your turntable would permanantly and irrepairably destroy your pre-amp
for any sort of serious listening.  His comments didn't exactly consider the
laws of physics, but he did get himself a considerable amount of press
coverage, and some flaming on net.audio. 
-- 
SUPPORT SECULAR TEDDY-BEAR-ISM.
"I see a dark cloud, On the horizon,..."

(ihnp4/allegra)!alice!jj

herbie@watdcsu.UUCP (Herb Chong - DCS) (08/23/85)

In article <4189@alice.UUCP> dsj@alice.UUCP (David S. Johnson) writes:
>This hypothesis is argued in Neil Levenson's audiophile column
>in the May/June 1985 issue of FANFARE (Levenson is a golden ear
>who would do THE ABSOLUTE SOUND proud).  He claims that digitally
>recorded vinyl discs generate ultrasonic products not present
>in analogue discs (he claims these have been measured), which
>somehow cause micro-cracks in turntable bearings (he claims
>these have been seen under electron microscopes) which by some
>mechanism greatly increase the short-term speed irregularities
>of the turntable, especially audible on piano music.

digital audio depends on filtering of both input and output to remove
high frequencies or else there'll be severe aliasing problems.  on
playback, the recorders use enough of a high frequency filter that a
good analog recording will also have the same ultrasonic energy.  the
cutter heads themselves resonate at a frquency of about 35kHz response
and can be excited by a typical high frequency signal, whether
digitally produced or analog.  another thing too is that surface wear
mechanisms of things like bearings is still poorly understood and an
area of active research.  unless the guy has a a PhD in materials
science, i can't believe his claims of ultrasonic signals causing the
cracks.  they will have the effects he describes though, as the flutter
will increase if the cracks get big enough, but more likely the result
will be increased rumble.

Herb Chong...

I'm user-friendly -- I don't byte, I nybble....

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seifert@hammer.UUCP (Snoopy) (08/25/85)

In article <4189@alice.UUCP> dsj@alice.UUCP (David S. Johnson) writes:

> ...  He claims that digitally
>recorded vinyl discs generate ultrasonic products not present
>in analogue discs (he claims these have been measured), which
>somehow cause micro-cracks in turntable bearings (he claims
>these have been seen under electron microscopes) which by some
>mechanism greatly increase the short-term speed irregularities
>of the turntable, especially audible on piano music.

Not to worry, the damage is easily repaired by playing an
analog record *backwards*.  The heavy vibes created by this
procedure actually melts the micro-cracks back together.
The best albums to use for this are by English rock bands
of the sixties.

Snoopy
tektronix!hammer!seifert

"I buried Paul."