From: shetline@bbn.com (Kerry Shetline)
Newsgroups: rec.audio
Subject: Re: How can different digital cables sound different?
Followup-To: rec.audio
Date: 7 Jan 1993 16:01:37 GMT
Organization: BBN
Distribution: world
NNTP-Posting-Host: bbn.com

In article <1993Jan6.215347@trc.amoco.com>, znpt01@trc.amoco.com (Norman P.
Tracy) wrote:
   (Some useful and reasonable information about jitter and clock recovery
    deleted)
> 
> 10. Then comes a certain group of audiophiles who declare digital audio by
> its very nature is already perfect.  They agrue this point using a selected
> subset of the facts and tenuous analogy to other usually purely digital
> technologies.  Their belief system includes a form of audio egalitarianism
> which has latched onto digital audio as a means to bring ultimate hi-fidelity
> down to the lowest common denominator.  Anyone questioning this belief system
> is to be labled self-delusional or a charlatan and immediantly challenged to
> a duel in the form of an ABX test.

Hey. I'll buy that bad and/or cheap designs might lead to audible effects,
as you have described above. Even subtle ones where this clock-recovery
issue comes in.

How do these bad DACs generally respond to jitter? Do they stretch and
shrink the time period in the analog output associated with each data word?
Or do words get dropped or doubled? At what rate is this likely to happen?

Also, do one-piece units (the standard CD-player with built-in DAC) bother
with complicated clock-recovery schemes, or do they just get their clock
from the sensible place -- the transport control and data-reading system?

Anyway, this thread was originally about digital audio cables. And I would
still claim that once a reasonable level of noise protection has been
achieved (and it doesn't take a $500 cable to do that) that a cable will
sound just the same as any other cable meeting that some easy-to-achieve
criterion. (And please, before *LAN Master* or someone else jumps in, we
are talking about generally 1-meter or shorter cables, with no
retransmission stations, no competing network traffic, etc. in a fairly
non-hostile environment.)

If we are careful about defining 'jitter' as a time-domain problem (I get
the feeling some people are confusing it with noise affecting signal
level), how can a 1-meter cable introduce jitter? Bits go in as electrical
pulses in one end and come out the other. They can't decide to sprint to
they other end, or hang out in the middle of the cable and take a coffee
break. So where would jitter come from? About the only thing that could add
real jitter would be the VERY VERY SLIGHT change that temperature
variations introduce to the speed of electrical signals through a given
medium. Then again, I'm sure that somebody out there believes they can here
this. After all, over a one meter cable, it wouldn't be measurable, and
non-measureability seems to be a chief criterion for what some golden-ears
can hear.)

I can see how noise might deform pulse edges and screw up clock recovery.
But that is still an issue of reasonable shielding and better DAC design.
Not a reason for high-priced cables.

As for optical-digital, I just can't see much room for anything to go wrong
on a short piece of fiber optics, with no competing traffic, at a bandwidth
which is a breeze for optical systems.

> down to the lowest common denominator.  Anyone questioning this belief system
> is to be labled self-delusional or a charlatan and immediantly challenged to

Some people are skilled listeners. But some are self-delusional. And I
reserve 'charlatan' for people who claim stupid reasons for certain
effects, be those effects real or imagined, and especially if they are
trying to sell you something.

It seems to me that the best approach to this jitter problem is a one-piece
CD-player with a good quality DAC and analog components. Either that, or if
clock-recovery is so difficult to do well, a new interface standard that
provides a separate clock signal. I'll ask the engineers: Is it really that
difficult to do clock recovery well? Or is it just bad design? Is there
much of a price difference?

-Kerry
Xref: sparky rec.audio:17836 rec.video:15422